2015 AP Chemistry free response 2 d e

WEBVTT
Kind: captions
Language: en

00:00:00.336 --> 00:00:02.677
- [Voiceover] The Lewis
electron-dot diagram

00:00:02.677 --> 00:00:06.545
for C_two H_four is shown
below in the box on the left.

00:00:06.545 --> 00:00:08.106
In the box on the right,

00:00:08.106 --> 00:00:11.033
complete the Lewis electron-dot diagram

00:00:11.033 --> 00:00:13.616
for C_two H_five OH or ethanol,

00:00:14.867 --> 00:00:17.695
by drawing in all of the electron pairs.

00:00:17.695 --> 00:00:19.288
So as they said, this right over here,

00:00:19.288 --> 00:00:23.189
this is the Lewis electron-dot
diagram for ethene

00:00:23.189 --> 00:00:25.205
and they want us to fill in all of the,

00:00:25.205 --> 00:00:26.502
they want us to draw in all

00:00:26.502 --> 00:00:29.428
the electron pairs for ethanol.

00:00:29.428 --> 00:00:32.354
And what we could do,
and I'll do it in a way

00:00:32.354 --> 00:00:35.507
where we can see which
electron comes from which atom,

00:00:35.507 --> 00:00:37.197
but they're not even
asking you to do that.

00:00:37.197 --> 00:00:39.928
But in blue, I'm going
to make the electrons

00:00:39.928 --> 00:00:41.358
from the hydrogens.

00:00:41.358 --> 00:00:44.024
So each hydrogen, you can
think of it as contributing

00:00:44.024 --> 00:00:46.202
one electron to each pair,

00:00:46.202 --> 00:00:48.250
and that's what's forming
the covalent bonds.

00:00:48.250 --> 00:00:51.891
So say this hydrogen is going
to contribute this electron,

00:00:51.891 --> 00:00:55.594
this hydrogen can
contribute this electron,

00:00:55.594 --> 00:00:59.919
this hydrogen can
contribute this electron,

00:00:59.919 --> 00:01:02.422
this hydrogen can
contribute that electron,

00:01:02.422 --> 00:01:04.991
this hydrogen can
contribute that electron,

00:01:04.991 --> 00:01:08.491
this hydrogen can contribute this electron

00:01:09.932 --> 00:01:11.265
right over there.

00:01:11.265 --> 00:01:13.151
And then, let's see.

00:01:13.151 --> 00:01:14.938
So now let's think about the carbons.

00:01:14.938 --> 00:01:16.108
And if you were actually
taking the EP test,

00:01:16.108 --> 00:01:18.384
you wouldn't, probably you
don't even have markers around,

00:01:18.384 --> 00:01:19.393
but I'm gonna do it in different colors

00:01:19.393 --> 00:01:20.562
just so you can see it.

00:01:20.562 --> 00:01:22.967
So each carbon has four valence electrons

00:01:22.967 --> 00:01:26.218
that it can contribute
for covalent bonding.

00:01:26.218 --> 00:01:29.718
So this carbon over here, that's one, two,

00:01:30.964 --> 00:01:32.714
three, and then four.

00:01:34.833 --> 00:01:36.880
And now this carbon
over here can contribute

00:01:36.880 --> 00:01:37.713
one, two,

00:01:40.407 --> 00:01:41.740
three, and four.

00:01:44.276 --> 00:01:46.714
And now we think about the oxygen.

00:01:46.714 --> 00:01:48.501
So oxygen's interesting.

00:01:48.501 --> 00:01:50.874
It's going to have two lone pairs.

00:01:50.874 --> 00:01:52.629
So it's gonna have one lone pair.

00:01:52.629 --> 00:01:53.670
I can do it there.

00:01:53.670 --> 00:01:56.303
One lone pair like that.

00:01:56.303 --> 00:01:58.286
And then, it's going to
have, it's going to form

00:01:58.286 --> 00:02:02.089
this bond by contributing
one electron to this pair

00:02:02.089 --> 00:02:04.657
and one electron to this
pair right over there.

00:02:04.657 --> 00:02:07.063
So each of these pairs
represent a covalent bond.

00:02:07.063 --> 00:02:08.786
This one I could have
drawn a little bit lower,

00:02:08.786 --> 00:02:10.964
but I think you get the idea.

00:02:10.964 --> 00:02:15.047
Those, I have drawn in
all of the electron pairs.

00:02:16.360 --> 00:02:18.051
And I'll just think about part e.

00:02:18.051 --> 00:02:19.448
What is the approximate value

00:02:19.448 --> 00:02:22.569
of the carbon-oxygen-hydrogen bond angle

00:02:22.569 --> 00:02:25.300
in the ethanol molecule.

00:02:25.300 --> 00:02:27.315
So, in the ethanol, they're really saying,

00:02:27.315 --> 00:02:30.891
so the ethanol molecule, they
want to know the bond angle.

00:02:30.891 --> 00:02:34.224
You have the oxygen bonded to a hydrogen

00:02:35.930 --> 00:02:38.180
bonded to the C_two H_five.

00:02:40.514 --> 00:02:42.140
So I'll just write that as,

00:02:42.140 --> 00:02:46.057
C_two, I'll just write
C_two H_five, like that.

00:02:47.139 --> 00:02:49.874
And they want to know
what is approximately

00:02:49.874 --> 00:02:52.182
this bond angle going to be.

00:02:52.182 --> 00:02:54.393
And the important thing to realize is,

00:02:54.393 --> 00:02:56.766
when you form these bonds with
oxygen, it's going to have

00:02:56.766 --> 00:02:59.171
pretty close to a tetrahedral shape.

00:02:59.171 --> 00:03:03.170
Why? Because the oxygen
has these two lone pairs.

00:03:03.170 --> 00:03:07.136
So these two lone pairs are
forming the other parts,

00:03:07.136 --> 00:03:08.886
the other, the other,

00:03:09.736 --> 00:03:13.800
I guess you could say points
of the tetrahedral shape.

00:03:13.800 --> 00:03:16.205
And so if we were
talking about just water,

00:03:16.205 --> 00:03:18.060
so, water, if we were talking about

00:03:18.060 --> 00:03:20.952
a water molecule right over here,

00:03:20.952 --> 00:03:22.739
and I'm not doing a
good job of drawing it.

00:03:22.739 --> 00:03:24.658
You could draw one electron pair there

00:03:24.658 --> 00:03:25.535
and then the other electron pair

00:03:25.535 --> 00:03:26.932
would be here in the back.

00:03:26.932 --> 00:03:29.502
Actually, I could, let
me draw it like this.

00:03:29.502 --> 00:03:33.046
Let me draw, I could draw it like this.

00:03:33.046 --> 00:03:34.311
If we were talking about water,

00:03:34.311 --> 00:03:37.887
I could draw one hydrogen popping out.

00:03:37.887 --> 00:03:41.235
I could draw the other
hydrogen popping in.

00:03:41.235 --> 00:03:44.682
And then one electron pair is over here

00:03:44.682 --> 00:03:47.216
and one electron pair is over here.

00:03:47.216 --> 00:03:49.492
This bond angle over here in water,

00:03:49.492 --> 00:03:51.215
this is, I guess, a semi-useful thing

00:03:51.215 --> 00:03:52.793
to know in general.

00:03:52.793 --> 00:03:54.237
You could kind of eyeball, and say,

00:03:54.237 --> 00:03:55.697
oh that looks like a little bit more

00:03:55.697 --> 00:03:57.420
than 100 degrees, and you'd be right.

00:03:57.420 --> 00:04:01.587
This is approximately 100
point four point five degrees.

00:04:02.829 --> 00:04:05.123
And this is actually not a
perfect tetrahedral shape.

00:04:05.123 --> 00:04:08.504
It gets distorted because
these lone pairs of electrons

00:04:08.504 --> 00:04:11.982
are repelling each other
and making these two get in

00:04:11.982 --> 00:04:14.422
a little bit closer
together with each other.

00:04:14.422 --> 00:04:16.891
And if you have a pure tetrahedral shape.

00:04:16.891 --> 00:04:18.808
So you have something in he middle.

00:04:18.808 --> 00:04:19.718
Well, let me just,

00:04:19.718 --> 00:04:22.514
if you had a pure
tetrahedral shape like this.

00:04:22.514 --> 00:04:25.017
So let me, so let me draw it like this.

00:04:25.017 --> 00:04:27.781
So something popping out.

00:04:27.781 --> 00:04:30.934
You have something, something going in.

00:04:30.934 --> 00:04:33.047
And then you have two things like this.

00:04:33.047 --> 00:04:35.030
That's one way to think
about a tetrahedron.

00:04:35.030 --> 00:04:36.103
There's others.

00:04:36.103 --> 00:04:37.923
Then the bond angle between all of these

00:04:37.923 --> 00:04:39.548
if it's a more, I guess you could say,

00:04:39.548 --> 00:04:43.775
symmetric tetra, a
non-distorted tetrahedral shape,

00:04:43.775 --> 00:04:45.192
is 109.5 degrees.

00:04:46.398 --> 00:04:48.106
And this is a reasonable,

00:04:48.106 --> 00:04:51.478
a reasonably useful number to know,

00:04:51.478 --> 00:04:52.725
obviously for this question as well.

00:04:52.725 --> 00:04:53.699
I don't know if you could,

00:04:53.699 --> 00:04:55.031
if this is obvious.

00:04:55.031 --> 00:04:56.851
Let me actually draw the tetra-hed,

00:04:56.851 --> 00:04:59.679
let me connect the tetrahedron.

00:04:59.679 --> 00:05:03.093
So, you could draw it like that,

00:05:03.093 --> 00:05:04.816
and then that would be the
other side right there.

00:05:04.816 --> 00:05:05.661
I don't know if that helps.

00:05:05.661 --> 00:05:07.774
Let me draw another one.

00:05:07.774 --> 00:05:10.691
So, if I were to draw a tetrahedron

00:05:12.000 --> 00:05:13.853
and if this was transparent,

00:05:13.853 --> 00:05:17.137
you have a molecule, or you have an atom

00:05:17.137 --> 00:05:19.964
in the middle, and then
you have the four bonds.

00:05:19.964 --> 00:05:21.797
One, two, three, four.

00:05:23.475 --> 00:05:25.556
I could say four bonds or lone pairs.

00:05:25.556 --> 00:05:29.619
Then, let me make sure you
see the one in the center,

00:05:29.619 --> 00:05:33.423
then the angle here is
approximately 109.5 degrees.

00:05:33.423 --> 00:05:36.348
So this is going to be tetrahedral,

00:05:36.348 --> 00:05:37.974
we have these lone pairs

00:05:37.974 --> 00:05:40.672
that are going to be repelling
each other a little bit.

00:05:40.672 --> 00:05:42.525
So you're going to be
someplace in the neighborhood,

00:05:42.525 --> 00:05:44.378
of, I don't know, around where water is

00:05:44.378 --> 00:05:46.328
or more pure tetrahedral shape.

00:05:46.328 --> 00:05:48.501
So I would say your bond
angle is going to be,

00:05:48.501 --> 00:05:51.951
I don't know, between 104 and 110 degrees.

00:05:51.951 --> 00:05:53.534
104 to 110 degrees.

00:05:56.015 --> 00:05:57.705
In fact, I would, I would estimate

00:05:57.705 --> 00:05:59.688
that it's going to be more than 104.5,

00:05:59.688 --> 00:06:02.021
because these, well, I just,

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I won't try to dig too much into it.

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They really just want us to approximate,

00:06:08.563 --> 00:06:10.482
approximate the value.

00:06:10.482 --> 00:06:13.374
So you could give anything in this range

00:06:13.374 --> 00:06:16.457
would be a suitable, suitable answer.


2015 AP Chemistry free response 2c

WEBVTT
Kind: captions
Language: en

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Because the dehydration reaction

00:00:02.176 --> 00:00:04.995
is not observed to occur at 298 Kelvin,

00:00:04.995 --> 00:00:06.829
the student claims that the reaction

00:00:06.829 --> 00:00:09.289
has an equilibrium constant less that

00:00:09.289 --> 00:00:12.699
one point zero zero at 298 Kelvin.

00:00:12.699 --> 00:00:15.129
Do the thermodynamic data for the reaction

00:00:15.129 --> 00:00:16.820
support the students claim?

00:00:16.820 --> 00:00:20.825
Justify your answer,
including a calculation

00:00:20.825 --> 00:00:23.600
of standard or change in standard

00:00:23.600 --> 00:00:26.073
Gibbs free energy at 298 Kelvin

00:00:26.073 --> 00:00:28.395
for the reaction.

00:00:28.395 --> 00:00:29.158
So lets first of all,

00:00:29.158 --> 00:00:30.767
let's review what the students claim is.

00:00:30.767 --> 00:00:31.712
The student claims that since the

00:00:31.712 --> 00:00:34.534
reaction is not observed at 298 Kelvin

00:00:34.534 --> 00:00:38.920
that at that temperature the reaction...

00:00:38.920 --> 00:00:41.476
The student claims that the reaction

00:00:41.476 --> 00:00:44.551
has an equilibrium constant
less than one point o

00:00:44.551 --> 00:00:46.701
at 298 Kelvin. That's their claim.

00:00:46.701 --> 00:00:51.074
And if the idea of equilibrium constant

00:00:51.074 --> 00:00:52.398
or Gibbs Free Energy

00:00:52.398 --> 00:00:53.710
are completely foreign to you

00:00:53.710 --> 00:00:56.130
I encourage you to review
the videos on Khan Academy

00:00:56.130 --> 00:00:58.664
on Gibbs Free Energy and
equilibrium constants.

00:00:58.664 --> 00:01:00.324
If they are familiar
to you but you're like,

00:01:00.324 --> 00:01:01.868
OK I don't know all the formulas

00:01:01.868 --> 00:01:03.703
that might connect the information

00:01:03.703 --> 00:01:05.363
that's given in the problem

00:01:05.363 --> 00:01:06.768
and how to calculate Delta G.

00:01:06.768 --> 00:01:08.969
And maybe how do we go from Delta G

00:01:08.969 --> 00:01:10.770
to equilibrium constants and figuring out

00:01:10.770 --> 00:01:12.164
whether the equilibrium constant

00:01:12.164 --> 00:01:13.707
is going to be greater
than or less than one

00:01:13.707 --> 00:01:15.158
or even equal to one.

00:01:15.158 --> 00:01:16.946
The good thing is that they give you

00:01:16.946 --> 00:01:18.107
all of the formulas that you need.

00:01:18.107 --> 00:01:20.151
It's on the first page of
the free response section.

00:01:20.151 --> 00:01:23.866
You just have to understand
which ones are applicable

00:01:23.866 --> 00:01:26.594
and what's actually going
on with those equations.

00:01:26.594 --> 00:01:27.871
So let's first of all think about

00:01:27.871 --> 00:01:31.614
whether we can calculate Delta G

00:01:31.614 --> 00:01:34.243
with the information that they've given.

00:01:34.243 --> 00:01:35.660
And if you go to the first page

00:01:35.660 --> 00:01:37.492
on one of the formulas they give you

00:01:37.492 --> 00:01:38.435
And you might even remember

00:01:38.435 --> 00:01:40.954
how to figure out whether a
reaction is spontaneous or not

00:01:40.954 --> 00:01:42.533
and how you can calculate Delta G

00:01:42.533 --> 00:01:43.729
based on the temperature,

00:01:43.729 --> 00:01:45.818
the change in entropy, and
the change in enthalpy.

00:01:45.818 --> 00:01:49.102
You have this formula right over here.

00:01:49.102 --> 00:01:50.521
And I literally just copied and pasted it

00:01:50.521 --> 00:01:52.428
from what they give you
when you take the test.

00:01:52.428 --> 00:01:56.407
And so they give us the change
in enthalpy for the reaction.

00:01:56.407 --> 00:01:58.310
They give us the temperature, 298 Kelvin.

00:01:58.310 --> 00:02:01.386
They give us the change in
entropy for the reaction.

00:02:01.386 --> 00:02:03.009
This is the change in standard entropy,

00:02:03.009 --> 00:02:05.111
change in standard
enthalpy for the reaction.

00:02:05.111 --> 00:02:07.155
And so using those we can figure out

00:02:07.155 --> 00:02:09.210
what Delta G is going to be.

00:02:09.210 --> 00:02:10.997
And then we can say,
"OK, is it consistent?

00:02:10.997 --> 00:02:13.761
Is it greater than zero?

00:02:13.761 --> 00:02:15.396
Which is conssistant

00:02:15.396 --> 00:02:17.098
with the reaction not being spontaneous

00:02:17.098 --> 00:02:18.340
which seems to be what's observed.

00:02:18.340 --> 00:02:19.745
And then how can we go from

00:02:19.745 --> 00:02:22.961
that Delta G to the equilibrium constant?"

00:02:22.961 --> 00:02:25.395
Well they also tell us that Delta G

00:02:25.395 --> 00:02:26.674
is equal to this second thing.

00:02:26.674 --> 00:02:28.933
And this connects Delta G
in the equilibrium constant.

00:02:28.933 --> 00:02:30.976
And we know some things about R and T.

00:02:30.976 --> 00:02:33.891
In fact we know exactly what
R and T are if we need them.

00:02:33.891 --> 00:02:36.019
So let's go ahead and apply

00:02:36.019 --> 00:02:38.514
these equations right over here.

00:02:38.514 --> 00:02:41.207
So you have... Actually let me just write

00:02:41.207 --> 00:02:42.900
all of the information we have first.

00:02:42.900 --> 00:02:46.878
So what is our change
in standard enthalpy?

00:02:46.878 --> 00:02:47.752
We're going to have to figure that out.

00:02:47.752 --> 00:02:48.900
We're going to have to figure out

00:02:48.900 --> 00:02:53.174
what our change in standard
entropy is going to be.

00:02:54.174 --> 00:02:55.425
We know what the temperature is.

00:02:55.425 --> 00:02:59.016
We know that that is 298 Kelvin.

00:02:59.016 --> 00:03:02.868
And we can worry about R
in a second if we need to.

00:03:02.868 --> 00:03:06.456
So up here when they gave us the reaction

00:03:06.456 --> 00:03:08.788
they gave us our change
in standard enthalpy

00:03:08.788 --> 00:03:11.599
and our change in standard
entropy at 298 Kelvin.

00:03:11.599 --> 00:03:12.691
This is very convenient.

00:03:12.691 --> 00:03:17.691
So our change in enthalpy
is 45.5 kilojoules per mole.

00:03:18.405 --> 00:03:23.405
Our change in standard entropy
is 126 joules per Kelvin-mole

00:03:23.780 --> 00:03:24.814
so this is very interesting.

00:03:24.814 --> 00:03:27.971
This is given in kilojoules,
this is given in joules.

00:03:27.971 --> 00:03:30.015
And so we wanna make sure
that we're being consistent.

00:03:30.015 --> 00:03:32.662
So let's just make sure that
everything is in joules.

00:03:32.662 --> 00:03:33.684
So I'm going to write this,

00:03:33.684 --> 00:03:37.271
this thing is the same as 45,500

00:03:37.271 --> 00:03:40.893
joules per mole for this reaction.

00:03:40.893 --> 00:03:42.217
So let me write this down,

00:03:42.217 --> 00:03:46.384
this is 45,500, this is
126 joules per Kelvin-mole.

00:03:47.444 --> 00:03:49.734
So this is,

00:03:50.954 --> 00:03:53.031
this right over here,

00:03:53.031 --> 00:03:56.222
is 45,500 joules per mole.

00:03:59.908 --> 00:04:03.908
This is 126 joules per Kelvin-mole.

00:04:06.049 --> 00:04:08.938
And now we can figure out what
the Delta G is going to be.

00:04:08.938 --> 00:04:12.522
Delta G is going to be equal to...

00:04:14.072 --> 00:04:18.931
Well our change in enthalpy
is 45,500 joules per mole

00:04:21.583 --> 00:04:25.583
minus our temperature, 298 Kelvin.

00:04:26.576 --> 00:04:28.590
Times our change in entropy.

00:04:28.590 --> 00:04:32.017
Times 126 joules per Kelvin-mole.

00:04:38.480 --> 00:04:40.566
And notice the Kelvin and then the Kelvin,

00:04:40.566 --> 00:04:41.686
those should both be capital Ks,

00:04:41.686 --> 00:04:44.117
capital K, cancel out.

00:04:44.117 --> 00:04:46.038
And the units here are
going to be joules per mole.

00:04:46.038 --> 00:04:47.666
The units here are going
to be joules per mole.

00:04:47.666 --> 00:04:49.674
And then we just figure
out the difference.

00:04:49.674 --> 00:04:51.538
So let's do this.

00:04:51.538 --> 00:04:54.283
Let me get my calculator out.

00:04:55.263 --> 00:04:57.134
And so this is going to be...

00:04:59.108 --> 00:05:00.704
Well let me multiply these two first.

00:05:00.704 --> 00:05:05.704
We're going to have 298
times 126 is equal to that.

00:05:06.700 --> 00:05:08.578
And let's see, I'm going
to subtract this from

00:05:08.578 --> 00:05:11.364
45,500 so let me just make it a negative.

00:05:11.364 --> 00:05:15.538
And add it to 45,500 is
going to be equal to...

00:05:19.978 --> 00:05:23.982
is going to be equal to 7,952.

00:05:23.982 --> 00:05:25.191
And if we want to stay...

00:05:25.191 --> 00:05:26.637
I mean we want to stay consistant

00:05:26.637 --> 00:05:28.456
with how many significant digits

00:05:28.456 --> 00:05:30.290
or significant figures we have.

00:05:30.290 --> 00:05:32.206
And it looks like it's pretty consistently

00:05:32.206 --> 00:05:33.483
three significant figures.

00:05:33.483 --> 00:05:34.934
So we want three significant figures here.

00:05:34.934 --> 00:05:38.219
So we could write 7,900, roughly 7,950.

00:05:40.784 --> 00:05:45.784
So our Delta G is approximately
7,950 joules per mole.

00:05:50.034 --> 00:05:52.460
And the fact that this
is greater than zero

00:05:52.460 --> 00:05:54.260
tells us that this is not going to be

00:05:54.260 --> 00:05:56.315
spontaneous at that temperature.

00:05:56.315 --> 00:05:58.103
So it's already consistent
with our observations.

00:05:58.103 --> 00:05:59.555
And that's always a good reality check.

00:05:59.555 --> 00:06:01.134
Because, are the things that you're seeing

00:06:01.134 --> 00:06:03.653
consistent with what the
question is describing?

00:06:03.653 --> 00:06:08.542
So Delta G greater than zero consistent.

00:06:09.582 --> 00:06:13.260
Consistent with reaction.

00:06:14.170 --> 00:06:18.660
Reaction being, or not being spontaneous.

00:06:20.081 --> 00:06:23.485
Not being spontaneous.

00:06:25.325 --> 00:06:29.719
Spontaneous at 298 kelvin.

00:06:30.726 --> 00:06:33.033
In the videos on Khan
Academy on Gibbs free energy

00:06:33.033 --> 00:06:34.587
we go into a lot more
detail on what this is.

00:06:34.587 --> 00:06:36.073
But one way to think about it is,

00:06:36.073 --> 00:06:38.720
this is the energy, the change in energy

00:06:38.720 --> 00:06:40.426
that's available to do work.

00:06:40.426 --> 00:06:44.138
And so if you have more, if
your Gibbs free energy increases

00:06:44.138 --> 00:06:45.601
over the course of the reaction,

00:06:45.601 --> 00:06:46.586
that means the products have

00:06:46.586 --> 00:06:48.189
more energy to do work.

00:06:48.189 --> 00:06:50.951
And so that means you
have to put work into it

00:06:50.951 --> 00:06:53.181
in order for the reaction
to actually proceed.

00:06:53.181 --> 00:06:55.560
If your Delta G is negative
that means your products

00:06:55.560 --> 00:06:59.787
have less energy to do
work than your reactants.

00:06:59.787 --> 00:07:01.540
Which means that it can
release that energy.

00:07:01.540 --> 00:07:03.664
It can do work, and it can be spontaneous.

00:07:03.664 --> 00:07:05.342
So this one, it's greater than zero.

00:07:05.342 --> 00:07:08.166
So it's not going to be spontaneous.

00:07:08.166 --> 00:07:09.919
But that doesn't answer
the question for us.

00:07:09.919 --> 00:07:12.043
We want to validate the claim that

00:07:12.043 --> 00:07:16.442
the reaction has an equilibrium
less than one at 298 Kelvin.

00:07:16.442 --> 00:07:19.095
And lucky for us they
also give us the formula

00:07:19.095 --> 00:07:23.286
that ties our Delta G to
our equilibrium constant.

00:07:23.286 --> 00:07:24.548
And we know the other things.

00:07:24.548 --> 00:07:27.289
We know R and we know T.

00:07:27.289 --> 00:07:29.381
And we might not actually
have to think about them.

00:07:29.381 --> 00:07:30.594
Because they're not telling us to

00:07:30.594 --> 00:07:32.202
calculate the equilibrium constant.

00:07:32.202 --> 00:07:33.708
They're just saying we'll validate that

00:07:33.708 --> 00:07:36.366
it's going to be less than one.

00:07:36.366 --> 00:07:41.366
And so, if we took 7,950 joules per mole

00:07:44.160 --> 00:07:47.387
is equal to negative RT times

00:07:47.387 --> 00:07:51.243
the natural log of our
equilibrium constant

00:07:51.243 --> 00:07:53.493
we'll solve for the equilibrium constant.

00:07:53.493 --> 00:07:58.493
Let's see, if I divide
both sides by negative RT.

00:07:58.855 --> 00:08:03.855
Negative RT. I'm going
to get the natural log.

00:08:06.289 --> 00:08:09.714
I'll just write it this
way, the natural log

00:08:09.714 --> 00:08:12.442
of my equilibrium constant
is going to be equal to

00:08:12.442 --> 00:08:17.442
7,950 joules per mole over negative RT.

00:08:22.984 --> 00:08:26.734
Or you could say E, this is just...

00:08:26.734 --> 00:08:29.346
What power do I raise E to to get K.

00:08:29.346 --> 00:08:34.346
Or so, you could say E to the
negative 7,950 joules per mole

00:08:38.054 --> 00:08:43.033
over RT is going t to be equal to K.

00:08:43.033 --> 00:08:44.809
And we could actually
calculate what this is.

00:08:44.809 --> 00:08:46.260
We know which R to use.

00:08:46.260 --> 00:08:48.526
We're dealing with joules and moles.

00:08:48.526 --> 00:08:51.252
So it would be this first Gas constant

00:08:51.252 --> 00:08:53.643
right over here eight point three one four

00:08:53.643 --> 00:08:55.618
joules per mole-kelvin.

00:08:55.618 --> 00:08:57.673
But we actually don't even have to do that

00:08:57.673 --> 00:08:58.959
because we just have to validate that K

00:08:58.959 --> 00:09:01.071
is going to be less than one.

00:09:01.071 --> 00:09:03.561
What happens if you raise
E to a negative exponent?

00:09:03.561 --> 00:09:06.382
And this is going to
be a negative exponent.

00:09:06.382 --> 00:09:11.101
This is positive, that is
positive, this is positive.

00:09:12.060 --> 00:09:15.375
We know it's 298 kelvin
positive, positive.

00:09:17.037 --> 00:09:19.917
So my entire exponent
is going to be negative.

00:09:19.917 --> 00:09:23.164
So negative, so negative.

00:09:25.132 --> 00:09:29.596
So you could say that K
equals E to negative number.

00:09:33.944 --> 00:09:36.706
I'll get this right. It's
kind of weird to write

00:09:36.706 --> 00:09:38.889
the negative and then the negative number.

00:09:38.889 --> 00:09:43.447
E to a negative number.

00:09:45.762 --> 00:09:47.417
Which must be less than one.

00:09:47.417 --> 00:09:50.707
Remember if the exponent is zero,

00:09:50.707 --> 00:09:52.334
E to the zero power is one,

00:09:52.334 --> 00:09:55.712
E to anything positive is
going to be greater than one.

00:09:55.712 --> 00:09:59.543
And E to anything negative
is going to be less than one.

00:09:59.543 --> 00:10:01.088
You wanna be careful, not less than zero.

00:10:01.088 --> 00:10:02.318
You actually can't get to less than zero.

00:10:02.318 --> 00:10:06.161
It's going to be less than one.

00:10:06.161 --> 00:10:09.017
And so this by itself already
validates the students claim.

00:10:09.017 --> 00:10:11.711
If you wanna go further you
could just calculate that.

00:10:11.711 --> 00:10:13.963
You could just say K is equal to

00:10:13.963 --> 00:10:18.963
E to the negative 7,950
joules per mole over R.

00:10:23.917 --> 00:10:26.574
Which is what? eight point three one four

00:10:26.574 --> 00:10:29.819
joules per mole kelvin.
Eight point three one four.

00:10:32.189 --> 00:10:35.967
Eight point three one four
joules per mole kelvin

00:10:38.908 --> 00:10:41.052
times 298 kelvin.

00:10:41.951 --> 00:10:44.930
Those cancel out and joules per mole

00:10:44.930 --> 00:10:46.558
divided by joules per mole.

00:10:46.558 --> 00:10:48.332
Those cancel out.

00:10:48.332 --> 00:10:50.343
And so, you would get your number.

00:10:50.343 --> 00:10:51.747
And actually let's just calculate it.

00:10:51.747 --> 00:10:54.413
Just for kicks, just to
really feel good about it.

00:10:54.413 --> 00:10:56.108
And you can see this is
going to be dimensionless.

00:10:56.108 --> 00:10:58.336
And equilibrium constants
are dimensionless.

00:10:58.336 --> 00:11:01.413
So we are going to get,
this is kind of fun.

00:11:01.413 --> 00:11:04.746
So let's see. Let's do
this denominator first.

00:11:04.746 --> 00:11:08.721
If you have eight point
three one four times 298

00:11:11.526 --> 00:11:14.116
Times 298. That's going
to be equal to that.

00:11:14.116 --> 00:11:15.683
Now we're dividing by that.

00:11:15.683 --> 00:11:17.179
So let me take the reciprocal of that

00:11:17.179 --> 00:11:20.907
and multiply it by 7,950.

00:11:20.907 --> 00:11:24.284
7,950 is equal to that.

00:11:24.284 --> 00:11:26.292
Now we want to raise E
to the negative of that.

00:11:26.292 --> 00:11:28.765
So lets make that negative and now

00:11:28.765 --> 00:11:30.901
let's raise E to that power.

00:11:30.901 --> 00:11:34.804
So lets see, we can raise E to that power.

00:11:34.804 --> 00:11:36.715
So we just press that
and there you have it.

00:11:36.715 --> 00:11:41.331
This is approximately
zero point four four zero.

00:11:41.331 --> 00:11:45.997
I guess you could say, well
let's just say four zero four.

00:11:45.997 --> 00:11:50.997
So this is approximately
zero point four zero four.

00:11:52.037 --> 00:11:55.168
Approximately, and I
already forgot the number,

00:11:55.168 --> 00:11:59.587
I have a bad memory, zero
point zero four zero four.

00:11:59.587 --> 00:12:02.977
zero point zero four zero four.

00:12:04.907 --> 00:12:06.559
And the whole rules of significant figures

00:12:06.559 --> 00:12:07.850
get a little bit trickier when you're

00:12:07.850 --> 00:12:09.382
starting to deal with exponents like this.

00:12:09.382 --> 00:12:10.915
So we're not going to,
and they don't ask us

00:12:10.915 --> 00:12:12.238
to calculate the exact value but

00:12:12.238 --> 00:12:14.932
hopefully this makes
you at least appreciate

00:12:14.932 --> 00:12:19.932
that the equilibrium concept
is for sure is less than one.


2015 AP Chemistry free response 2f

WEBVTT
Kind: captions
Language: en

00:00:00.489 --> 00:00:03.182
- [Voiceover] During the
dehydration experiment,

00:00:03.182 --> 00:00:06.213
ethene gas and unreacted ethanol

00:00:06.213 --> 00:00:09.501
passed through the tube into the water.

00:00:09.501 --> 00:00:13.089
The ethene was quantitatively
collected as a gas,

00:00:13.089 --> 00:00:16.085
but the unreacted ethanol was not.

00:00:16.085 --> 00:00:18.153
Explain this observation in terms

00:00:18.153 --> 00:00:21.125
of the intermolecular forces between water

00:00:21.125 --> 00:00:23.145
and each of the two gases.

00:00:23.145 --> 00:00:24.678
And just to be clear, what
they're talking about,

00:00:24.678 --> 00:00:27.464
we can go to the original
setup that they gave us

00:00:27.464 --> 00:00:29.949
at the beginning of this problem.

00:00:29.949 --> 00:00:32.236
And what they're saying is is,

00:00:32.236 --> 00:00:34.780
when they warm up, they'll react,

00:00:34.780 --> 00:00:37.241
the catalyst and the ethanol in here.

00:00:37.241 --> 00:00:41.072
Some of that ethanol gets
converted into ethene,

00:00:41.072 --> 00:00:42.060
but not all of it does.

00:00:42.060 --> 00:00:43.024
In fact, part of this experiment,

00:00:43.024 --> 00:00:44.719
we saw that we don't have a perfect,

00:00:44.719 --> 00:00:48.272
we have a 60-point-something
percent yield.

00:00:48.272 --> 00:00:51.500
And so you have a combination
of ethanol and ethene gas

00:00:51.500 --> 00:00:53.079
going through this tube.

00:00:53.079 --> 00:00:56.701
It cools down, then it
goes through this water.

00:00:56.701 --> 00:00:58.930
And they're saying it looks
like we're only seeing,

00:00:58.930 --> 00:01:01.600
or we're primarily seeing,
the ethene gas here.

00:01:01.600 --> 00:01:04.573
How come we're not seeing the ethanol gas?

00:01:04.573 --> 00:01:07.023
And the reason, and I'll
just paraphrase it right now,

00:01:07.023 --> 00:01:10.518
and then I'll write it down,
is that the ethanol gas

00:01:10.518 --> 00:01:13.676
is much more dissolvable in the water,

00:01:13.676 --> 00:01:16.277
because ethanol is a polar molecule,

00:01:16.277 --> 00:01:18.297
water is a polar solvent,

00:01:18.297 --> 00:01:21.850
so it's going to dissolve
much better in water

00:01:21.850 --> 00:01:25.867
than the ethene, which
isn't a polar molecule.

00:01:25.867 --> 00:01:28.328
So let me write this down.

00:01:28.328 --> 00:01:30.487
So the ethene will kind of bubble through,

00:01:30.487 --> 00:01:33.808
while the ethanol can actually dissolve.

00:01:33.808 --> 00:01:36.687
So let's write this down.

00:01:36.687 --> 00:01:40.286
So, whoops, having trouble,
all right, there you go.

00:01:40.286 --> 00:01:42.028
So explain this observation in terms

00:01:42.028 --> 00:01:43.842
of intermolecular forces between water

00:01:43.842 --> 00:01:45.839
and each of the two gases.

00:01:45.839 --> 00:01:48.006
So we could write ethanol.

00:01:49.136 --> 00:01:49.969
Ethanol

00:01:52.412 --> 00:01:53.245
is polar,

00:01:55.975 --> 00:01:57.225
so it dissolves

00:02:01.946 --> 00:02:02.779
in water

00:02:06.427 --> 00:02:07.344
much better

00:02:13.541 --> 00:02:14.541
than ethene,

00:02:17.229 --> 00:02:18.062
which is

00:02:20.665 --> 00:02:21.498
nonpolar.

00:02:25.241 --> 00:02:27.772
And so we could say something like,

00:02:27.772 --> 00:02:28.689
so ethanol,

00:02:29.815 --> 00:02:30.648
ethanol

00:02:33.243 --> 00:02:34.076
and water

00:02:36.447 --> 00:02:38.481
will have hydrogen bonds,

00:02:38.481 --> 00:02:40.564
will have hydrogen bonds.

00:02:43.452 --> 00:02:45.507
Hydrogen bonds.

00:02:45.507 --> 00:02:47.597
You could even diagram it out if you like.

00:02:47.597 --> 00:02:49.571
The ethanol is right over here.

00:02:49.571 --> 00:02:52.380
So you have your oxygen,

00:02:52.380 --> 00:02:54.470
and then you have your hydrogen,

00:02:54.470 --> 00:02:56.803
and then you have your C2H5.

00:02:58.812 --> 00:03:02.133
This side over here, this is
going to be partially negative.

00:03:02.133 --> 00:03:04.617
This is going to be partially positive.

00:03:04.617 --> 00:03:07.659
Oxygen is more
electronegative than carbon.

00:03:07.659 --> 00:03:10.086
The difference is less than
between oxygen and hydrogen,

00:03:10.086 --> 00:03:12.083
but this is also going
to be partially positive.

00:03:12.083 --> 00:03:13.569
Maybe not as partially positive

00:03:13.569 --> 00:03:15.706
as on this side right over here.

00:03:15.706 --> 00:03:17.656
And so when you have water molecules,

00:03:17.656 --> 00:03:20.141
so if this is a water molecule

00:03:20.141 --> 00:03:21.474
right over here,

00:03:22.766 --> 00:03:25.552
where this was partially positive charges,

00:03:25.552 --> 00:03:27.802
partially negative charges,

00:03:28.862 --> 00:03:32.195
you're going to have the hydrogen bonds.

00:03:34.216 --> 00:03:36.155
Hydrogen bonds.

00:03:36.155 --> 00:03:39.220
And so the ethanol is going
to dissolve much better.

00:03:39.220 --> 00:03:41.053
The ethene isn't polar

00:03:41.936 --> 00:03:46.395
and will only have induced
dipole forces acting on it.

00:03:46.395 --> 00:03:47.319
So let me write this.

00:03:47.319 --> 00:03:48.152
Ethene,

00:03:50.020 --> 00:03:51.687
ethene is not polar.

00:03:53.257 --> 00:03:54.340
Is not polar.

00:03:55.718 --> 00:03:57.635
And so, or I could say,

00:03:58.720 --> 00:03:59.553
so will

00:04:01.586 --> 00:04:02.419
only have

00:04:06.196 --> 00:04:08.959
induced dipole interactions.

00:04:08.959 --> 00:04:10.209
Induced dipole.

00:04:12.187 --> 00:04:13.487
And maybe well I could say dipole,

00:04:13.487 --> 00:04:15.654
'cause the water is polar,

00:04:17.086 --> 00:04:20.082
and even though ethene
is a symmetric molecule

00:04:20.082 --> 00:04:21.591
and has that double bond,

00:04:21.591 --> 00:04:24.122
it has no net polarity.

00:04:24.122 --> 00:04:25.933
There are parts of the ethene molecule

00:04:25.933 --> 00:04:26.990
that are going to be a little bit

00:04:26.990 --> 00:04:29.058
more negative than others,

00:04:29.058 --> 00:04:32.693
in particular, when you look
at the carbons over here.

00:04:32.693 --> 00:04:34.204
They're a little bit more electronegative

00:04:34.204 --> 00:04:35.597
than the hydrogens.

00:04:35.597 --> 00:04:38.128
And so ethene is not polar,

00:04:38.128 --> 00:04:41.240
wo will only have induced dipole,

00:04:41.240 --> 00:04:44.258
or I guess we could also say just dipole

00:04:44.258 --> 00:04:45.341
interactions,

00:04:46.709 --> 00:04:48.959
interactions, interactions,

00:04:50.599 --> 00:04:51.941
with

00:04:51.941 --> 00:04:52.941
polar water.

00:04:53.989 --> 00:04:54.989
Polar water.

00:04:56.445 --> 00:04:58.780
And so this is why.

00:04:58.780 --> 00:05:00.591
So this is why

00:05:00.591 --> 00:05:02.797
ethene won't dissolve as well.

00:05:02.797 --> 00:05:03.797
Ethene won't

00:05:06.582 --> 00:05:07.415
dissolve

00:05:09.182 --> 00:05:10.015
as well

00:05:11.574 --> 00:05:13.241
and bubbles through.

00:05:14.105 --> 00:05:15.772
And bubbles through.

00:05:18.540 --> 00:05:19.608
Ethanol dissolves.

00:05:19.608 --> 00:05:20.839
Ethene bubbles through,

00:05:20.839 --> 00:05:24.866
'cause it doesn't have strong
interactions with the water.


AP US history multiple choice example 2

WEBVTT
Kind: captions
Language: en

00:00:00.213 --> 00:00:01.536
- [Voiceover] Alright
so in the last video,

00:00:01.536 --> 00:00:04.253
we were taking a look at
this multiple choice question

00:00:04.253 --> 00:00:06.993
from the AP US History
exam practice booklet

00:00:06.993 --> 00:00:10.034
and trying out some strategies
for making good choices

00:00:10.034 --> 00:00:11.753
as you go through these questions.

00:00:11.753 --> 00:00:14.028
Now the first thing we did was really

00:00:14.028 --> 00:00:16.838
dive into the specifics
of what was happening

00:00:16.838 --> 00:00:19.740
in both of these quotes.

00:00:19.740 --> 00:00:22.039
Who James Henry Hammond is,

00:00:22.039 --> 00:00:24.198
he's a governor of South Carolina

00:00:24.198 --> 00:00:27.191
who was in favor of slavery

00:00:27.191 --> 00:00:29.605
in the mid-19th century

00:00:29.605 --> 00:00:32.160
who was giving some religious reasons

00:00:32.160 --> 00:00:35.317
and reasons of kindness for why slavery

00:00:35.317 --> 00:00:39.450
was a institution sanctioned
by God and society,

00:00:39.450 --> 00:00:42.144
and Frederick Douglass,
famous abolitionist,

00:00:42.144 --> 00:00:44.744
who's saying that slavery is the great sin

00:00:44.744 --> 00:00:46.695
and shame of America.

00:00:46.695 --> 00:00:50.110
So our first step was
analyzing the documents.

00:00:55.444 --> 00:00:57.464
And then our second step was

00:00:57.464 --> 00:01:01.283
to read each of our
questions really carefully.

00:01:01.283 --> 00:01:05.300
And both the questions and
the possible answer choices,

00:01:05.300 --> 00:01:07.111
you need to give them your full attention

00:01:07.111 --> 00:01:09.851
because you might skip
over an important word

00:01:09.851 --> 00:01:11.569
that makes the meaning different than what

00:01:11.569 --> 00:01:13.543
you thought it was at first glance.

00:01:13.543 --> 00:01:15.191
The third thing we're doing is going

00:01:15.191 --> 00:01:17.558
through each of the options

00:01:17.558 --> 00:01:20.630
and deciding whether
or not it's a possible

00:01:20.630 --> 00:01:22.186
before eliminating it.

00:01:22.186 --> 00:01:25.018
So let's try an example of
a multiple choice question

00:01:25.018 --> 00:01:26.620
related to these documents.

00:01:26.620 --> 00:01:29.360
The language used in both excerpts

00:01:29.360 --> 00:01:31.914
most directly reflects the influence

00:01:31.914 --> 00:01:33.818
of which of the following?

00:01:33.818 --> 00:01:35.420
So they're specifically asking us

00:01:35.420 --> 00:01:37.417
about the language.

00:01:37.417 --> 00:01:39.530
That means, the words that they're using,

00:01:39.530 --> 00:01:40.970
their phrases.

00:01:40.970 --> 00:01:43.431
Not maybe their political positions

00:01:43.431 --> 00:01:47.146
or the ideas that they're
trying to get across,

00:01:47.146 --> 00:01:49.236
but specifically the words.

00:01:49.236 --> 00:01:52.324
And we're looking for the influence

00:01:52.324 --> 00:01:56.387
of one of these four ideologies.

00:01:56.387 --> 00:01:59.336
OK, option A, The Second Great Awakening.

00:01:59.336 --> 00:02:02.238
Hmm, alright, well, I'm gonna say

00:02:02.238 --> 00:02:05.269
that's a religious movement of some kind.

00:02:05.269 --> 00:02:08.033
And they both talk about God

00:02:08.033 --> 00:02:11.399
and the relationship between
slavery and Christianity

00:02:11.399 --> 00:02:13.512
so I'm gonna leave that as a possible.

00:02:13.512 --> 00:02:15.207
Alright, what about States' rights?

00:02:15.207 --> 00:02:16.879
Well, I imagine that both these people

00:02:16.879 --> 00:02:19.572
would've had very different
ideas about states' rights,

00:02:19.572 --> 00:02:21.592
but I'm not sure that's
what they're talking about

00:02:21.592 --> 00:02:24.489
in these examples cuz
Hammond is talking about

00:02:24.489 --> 00:02:28.249
the duty of slave owners to be kind,

00:02:28.249 --> 00:02:30.548
and maybe the religious reasons why

00:02:30.548 --> 00:02:34.727
God has made the institution
of slavery, in his opinion.

00:02:34.727 --> 00:02:38.233
And Douglass is talking
about how slavery is

00:02:38.233 --> 00:02:41.971
against the Bible and
against the idea of liberty,

00:02:41.971 --> 00:02:45.013
so neither of them is
particularly concerned

00:02:45.013 --> 00:02:47.080
with the political issue
of states' rights here.

00:02:47.080 --> 00:02:49.727
So I think we can cross that one out.

00:02:49.727 --> 00:02:51.584
Alright, Manifest Destiny.

00:02:51.584 --> 00:02:55.230
Manifest Destiny was this
idea that the United States

00:02:55.230 --> 00:02:58.798
had a divine mission to occupy

00:02:58.798 --> 00:03:02.606
the North American continent
from Atlantic to Pacific.

00:03:02.606 --> 00:03:05.700
While they both kind of talk
about ideas of divinity,

00:03:05.700 --> 00:03:10.356
I don't think they're interested
in any kind of pioneering.

00:03:10.356 --> 00:03:15.018
This is more connected
to the American West

00:03:15.018 --> 00:03:18.579
than it is to any idea about slavery.

00:03:18.579 --> 00:03:20.761
So I think we can get rid of that.

00:03:20.761 --> 00:03:23.640
Alright, option D, American nationalism.

00:03:23.640 --> 00:03:26.682
Well, I think Douglass is, if anything,

00:03:26.682 --> 00:03:30.095
he's kind of saying
that slavery challenges

00:03:30.095 --> 00:03:31.744
American nationalism.

00:03:31.744 --> 00:03:33.323
Well I guess he talks about it then,

00:03:33.323 --> 00:03:36.922
maybe a nationalist view
of the idea of liberty

00:03:36.922 --> 00:03:39.313
would say that slavery
is a sin and a shame.

00:03:39.313 --> 00:03:40.915
So that's possible for Douglass.

00:03:40.915 --> 00:03:42.448
But what about for Hammond?

00:03:42.448 --> 00:03:45.025
He's really making cultural
and religious arguments

00:03:45.025 --> 00:03:47.510
for slavery, not any argument about

00:03:47.510 --> 00:03:50.389
how slavery enhances the American nation.

00:03:50.389 --> 00:03:52.664
So I'm gonna cross that one out too.

00:03:52.664 --> 00:03:54.891
So that leaves us with The
Second Great Awakening.

00:03:54.891 --> 00:03:56.974
And I think that is a good answer because

00:03:56.974 --> 00:03:59.412
both of them are making
religious arguments.

00:03:59.412 --> 00:04:01.571
They're saying that God would have liked,

00:04:01.571 --> 00:04:03.777
or would not have liked, slavery.

00:04:03.777 --> 00:04:08.138
So their language does reflect
an interest in religion.

00:04:10.108 --> 00:04:13.118
We'll do some other
examples in other videos,

00:04:13.118 --> 00:04:15.509
but I think the big takeaway from this is,

00:04:15.509 --> 00:04:18.979
don't worry about having every idea

00:04:18.979 --> 00:04:21.569
and every fact about American history

00:04:21.569 --> 00:04:23.492
stored away in your brain somewhere.

00:04:23.492 --> 00:04:27.254
Instead, understand that what
this exam is really going for

00:04:27.254 --> 00:04:31.712
is finding out whether you
have a good overall idea

00:04:31.712 --> 00:04:34.637
of what happened in American history,

00:04:34.637 --> 00:04:37.424
and who might have supported which idea.

00:04:37.424 --> 00:04:39.026
And trust your instincts.

00:04:39.026 --> 00:04:40.442
They're usually right.

00:04:40.442 --> 00:04:43.995
The point is not to test
you on some obscure outlier,

00:04:43.995 --> 00:04:46.038
but rather to get a sense that you know

00:04:46.038 --> 00:04:49.010
what you're talking about
in each era of history,

00:04:49.010 --> 00:04:52.725
and the general idea of what was going on.

00:04:52.725 --> 00:04:54.536
So use that to your advantage.

00:04:54.536 --> 00:04:57.996
Understand the big, underlying themes.

00:04:57.996 --> 00:05:01.409
And don't worry about the
little ticky-tack details.

00:05:01.409 --> 00:05:02.580
You know what you're doing.


AP US history multiple choice example 1

WEBVTT
Kind: captions
Language: en

00:00:01.046 --> 00:00:03.484
- [Kim] So this
video is about the multiple

00:00:03.484 --> 00:00:07.617
choice section on the
AP U.S. history exam.

00:00:07.617 --> 00:00:10.032
And now I know you're thinking

00:00:10.032 --> 00:00:13.152
Whoa, Kim, this is a
multiple choice section.

00:00:13.152 --> 00:00:16.147
How much help could we
possibly need with this?

00:00:16.147 --> 00:00:18.910
Either you know the answer or you don't.

00:00:18.910 --> 00:00:21.186
Au contraire mon ami.

00:00:21.186 --> 00:00:24.506
Thankfully the multiple
choice section on this exam

00:00:24.506 --> 00:00:27.780
is not just a laundry list of facts

00:00:27.780 --> 00:00:29.777
that you know or you don't know

00:00:29.777 --> 00:00:31.844
or you just leave blank.

00:00:31.844 --> 00:00:33.167
What's really great about the way

00:00:33.167 --> 00:00:35.466
these questions are designed

00:00:35.466 --> 00:00:38.717
is that they really reward
you for having intuition

00:00:38.717 --> 00:00:41.642
about what's going on in any time period

00:00:41.642 --> 00:00:43.523
in American history.

00:00:43.523 --> 00:00:46.054
So you might not necessarily need to know

00:00:46.054 --> 00:00:50.095
a pop quiz of facts about
slavery in the 19th century,

00:00:50.095 --> 00:00:54.117
but if you have a general idea of who

00:00:54.117 --> 00:00:55.610
the major players are,

00:00:55.610 --> 00:00:57.305
what the major ideas are,

00:00:57.305 --> 00:00:59.767
then you'll actually
prosper in this section,

00:00:59.767 --> 00:01:01.322
more than you might think.

00:01:01.322 --> 00:01:04.596
So let's take a look at
these quotes over here.

00:01:04.596 --> 00:01:07.058
Now each of the questions
on the multiple choice

00:01:07.058 --> 00:01:10.332
portion of the exam will relate back to

00:01:10.332 --> 00:01:14.117
a series of quotes like
this or maybe a chart

00:01:14.117 --> 00:01:16.694
or a political cartoon.

00:01:16.694 --> 00:01:18.459
The good news is that they're not

00:01:18.459 --> 00:01:20.177
just independent of each other.

00:01:20.177 --> 00:01:23.358
They're always going to
relate back to that chart,

00:01:23.358 --> 00:01:26.075
that graph, that political cartoon.

00:01:26.075 --> 00:01:29.804
So these two quotes

00:01:29.804 --> 00:01:32.464
are actually related to four questions,

00:01:32.464 --> 00:01:35.529
and each set of quotes or cartoon

00:01:35.529 --> 00:01:37.457
will have about two to four questions

00:01:37.457 --> 00:01:38.827
that go with it.

00:01:38.827 --> 00:01:42.101
So you should really spend
a lot of time reading

00:01:42.101 --> 00:01:45.096
these documents and
reading them carefully.

00:01:45.096 --> 00:01:47.139
And before you even go about trying

00:01:47.139 --> 00:01:48.904
to answer the questions,

00:01:48.904 --> 00:01:52.712
try to get a sense of who the
people are who are speaking,

00:01:52.712 --> 00:01:54.291
what their main points are,

00:01:54.291 --> 00:01:56.683
and how they're making their argument,

00:01:56.683 --> 00:01:59.725
before you even take a stab
at any of the questions.

00:01:59.725 --> 00:02:02.116
So let's do that with what we have here.

00:02:02.116 --> 00:02:05.483
So this is a real practice
question from the AP exam,

00:02:05.483 --> 00:02:07.457
and it consists of two quotes,

00:02:07.457 --> 00:02:10.174
one from James Henry Hammond,

00:02:10.174 --> 00:02:13.169
and one from Frederick Douglass.

00:02:13.169 --> 00:02:16.164
Now Douglass you've
probably heard of before.

00:02:16.164 --> 00:02:18.881
James Henry Hammond maybe not so much.

00:02:18.881 --> 00:02:21.139
All right, well first let's think about

00:02:21.139 --> 00:02:22.156
where they are in time.

00:02:22.156 --> 00:02:25.383
So we've got Hammond in 1845

00:02:25.383 --> 00:02:28.797
and Douglass in 1852.

00:02:28.797 --> 00:02:31.444
So it's the late Antebellum Period

00:02:31.444 --> 00:02:34.485
getting into the period
just before the Civil War.

00:02:34.485 --> 00:02:36.157
We know there are a lot of arguments

00:02:36.157 --> 00:02:38.410
about slavery and whether it should exist

00:02:38.410 --> 00:02:39.989
at this time period.

00:02:39.989 --> 00:02:42.636
So, all right, that's
a pretty easy baseline

00:02:42.636 --> 00:02:44.493
for where we are in time.

00:02:44.493 --> 00:02:46.444
Okay, now where are we in space?

00:02:46.444 --> 00:02:48.464
Well we know that James Henry Hammond

00:02:48.464 --> 00:02:50.739
is from South Carolina.

00:02:50.739 --> 00:02:52.063
What about Frederick Douglass?

00:02:52.063 --> 00:02:54.849
Do we have any clues as to where he is?

00:02:54.849 --> 00:02:57.496
Well, there's nothing listed here,

00:02:57.496 --> 00:03:00.306
but let's move into who
these people actually are.

00:03:00.306 --> 00:03:02.280
So we've got Frederick Douglass

00:03:02.280 --> 00:03:05.972
and he's a pretty key
figure in American history.

00:03:05.972 --> 00:03:09.455
So Frederick Douglass we know was

00:03:09.455 --> 00:03:13.240
a former enslaved person who escaped

00:03:15.390 --> 00:03:18.252
and he was very active

00:03:18.252 --> 00:03:21.201
in the abolitionist movement.

00:03:21.201 --> 00:03:24.800
The abolitionists were the group of

00:03:24.800 --> 00:03:28.445
mostly Northern intellectuals who believed

00:03:28.445 --> 00:03:31.534
that slavery should be
ended right this minute

00:03:31.534 --> 00:03:33.345
everywhere in the United States,

00:03:33.345 --> 00:03:34.529
if not the world.

00:03:34.529 --> 00:03:36.921
So this is probably a pretty good clue

00:03:36.921 --> 00:03:40.817
that we're looking at
someone from the North.

00:03:40.817 --> 00:03:43.236
What about James Henry Hammond?

00:03:43.236 --> 00:03:44.560
Have you heard of him before?

00:03:44.560 --> 00:03:48.786
Probably not, but we do
know some things about him.

00:03:48.786 --> 00:03:51.967
We know that he's in South Carolina,

00:03:51.967 --> 00:03:54.939
southern part of the country.

00:03:54.939 --> 00:03:57.377
And we know that he's a governor,

00:03:57.377 --> 00:04:00.025
so we can reasonably assume that

00:04:00.025 --> 00:04:02.718
he's pretty elite.

00:04:02.718 --> 00:04:05.551
We can be pretty certain
since this is before

00:04:05.551 --> 00:04:09.105
the Civil War that he's white.

00:04:10.025 --> 00:04:13.562
So you see that I'm
making some assumptions

00:04:13.562 --> 00:04:16.418
about who James Henry Hammond is here.

00:04:16.418 --> 00:04:19.251
I think he's probably a wealthy person.

00:04:19.251 --> 00:04:21.452
I think he's probably white.

00:04:21.452 --> 00:04:23.194
And you may be saying to yourself

00:04:23.194 --> 00:04:24.027
whoa, whoa, whoa.

00:04:24.027 --> 00:04:26.860
What if James Henry Hammond was

00:04:26.860 --> 00:04:29.507
the one exception to the rule

00:04:29.507 --> 00:04:31.806
and he was from the working class

00:04:31.806 --> 00:04:34.987
or he was that one
African American governor

00:04:34.987 --> 00:04:38.122
that we never talk about
from before the Civil War?

00:04:38.122 --> 00:04:40.165
Basically the question you're asking is

00:04:40.165 --> 00:04:41.558
could this be a trick?

00:04:41.558 --> 00:04:43.602
And the answer is generally no.

00:04:43.602 --> 00:04:47.178
Almost never is the AP U.S. history exam

00:04:47.178 --> 00:04:50.405
going to try to trick
you with that one strange

00:04:50.405 --> 00:04:52.054
exception to the rule,

00:04:52.054 --> 00:04:55.189
because they want you
to build this intuition.

00:04:55.189 --> 00:04:56.280
They want to say

00:04:56.280 --> 00:04:58.927
all right, what do you
know about American history

00:04:58.927 --> 00:05:00.970
and how can you fit these questions

00:05:00.970 --> 00:05:02.549
into that rubric?

00:05:02.549 --> 00:05:04.894
You even have kind of a
clue that you probably

00:05:04.894 --> 00:05:06.450
shouldn't know who this guy is

00:05:06.450 --> 00:05:08.261
because they have to explain who he is

00:05:08.261 --> 00:05:09.237
in the first place.

00:05:09.237 --> 00:05:10.049
Right?

00:05:10.049 --> 00:05:12.673
They have to say this was a
governor of South Carolina.

00:05:12.673 --> 00:05:14.020
Whereas Frederick Douglass,

00:05:14.020 --> 00:05:15.645
you can be pretty sure
that you've heard of him

00:05:15.645 --> 00:05:17.433
and you know what he was about.

00:05:17.433 --> 00:05:20.011
So trust your instincts
here because people

00:05:20.011 --> 00:05:22.797
are gonna be more or less who they seem

00:05:22.797 --> 00:05:25.096
in these circumstances.

00:05:25.096 --> 00:05:27.395
All right, let's finally
read these quotes.

00:05:27.395 --> 00:05:30.042
"Still though a slaveholder,
I freely acknowledge

00:05:30.042 --> 00:05:32.735
"my obligations as a man and I am bound

00:05:32.735 --> 00:05:35.127
"to treat humanely the fellow creatures

00:05:35.127 --> 00:05:37.983
"whom God has entrusted to my charge.

00:05:37.983 --> 00:05:40.235
"It is certainly in the interest of all

00:05:40.235 --> 00:05:42.511
"and I am convinced it is the desire

00:05:42.511 --> 00:05:45.019
"of every one of us to treat our slaves

00:05:45.019 --> 00:05:47.248
"with proper kindness."

00:05:47.248 --> 00:05:49.059
All right, so what is he saying here?

00:05:49.059 --> 00:05:52.681
First, he's saying he
himself is a slaveholder,

00:05:52.681 --> 00:05:55.909
so we've got a good idea of who he is.

00:05:55.909 --> 00:05:58.904
He's a wealthy, white
person who owns slaves

00:05:58.904 --> 00:06:00.553
in the South.

00:06:00.553 --> 00:06:04.690
So we can guess that he's
probably pro-slavery.

00:06:08.130 --> 00:06:09.918
What else is he saying?

00:06:09.918 --> 00:06:13.610
He's saying that slaveholders should treat

00:06:13.610 --> 00:06:17.432
enslaved people with kindness.

00:06:17.432 --> 00:06:20.543
All right, he says that he's
convinced it's the desire

00:06:20.543 --> 00:06:22.377
of every one of us.

00:06:22.377 --> 00:06:24.251
Well, this doesn't quite seem to jive

00:06:24.251 --> 00:06:27.502
with what we know about
slavery in the South.

00:06:27.502 --> 00:06:30.288
It's a cruel and terrible institution.

00:06:30.288 --> 00:06:33.330
So it sounds like Hammond might be making

00:06:33.330 --> 00:06:36.831
kind of an excuse for slavery?

00:06:38.764 --> 00:06:42.961
Or at least say maybe
slavery is not so bad?

00:06:49.282 --> 00:06:50.838
And I think there's one other thing

00:06:50.838 --> 00:06:52.254
kind of lurking in here,

00:06:52.254 --> 00:06:56.179
which is this idea that God has trusted

00:06:56.179 --> 00:06:59.476
fellow creatures to his charge.

00:06:59.476 --> 00:07:03.145
So he's almost saying that God made

00:07:03.145 --> 00:07:04.816
the system of slavery.

00:07:04.816 --> 00:07:07.185
That the way things
are is the way that God

00:07:07.185 --> 00:07:08.601
wanted them to be.

00:07:08.601 --> 00:07:12.340
So this is almost a religious
argument for slavery,

00:07:12.340 --> 00:07:15.080
saying God wanted it to be this way,

00:07:15.080 --> 00:07:18.354
God has entrusted these
people to his care.

00:07:18.354 --> 00:07:20.351
So what's Frederick Douglass saying here?

00:07:20.351 --> 00:07:24.043
He's saying, "Standing
with God and the crushed

00:07:24.043 --> 00:07:27.572
"and bleeding slave on
this occasion, I will,

00:07:27.572 --> 00:07:30.358
"in the name of humanity
which is outraged,

00:07:30.358 --> 00:07:32.913
"and in the name of
Liberty which is fettered,

00:07:32.913 --> 00:07:35.165
"in the name of the
constitution and Bible,

00:07:35.165 --> 00:07:37.255
"which are disregarded and trampled upon,

00:07:37.255 --> 00:07:40.204
"dare to call in question
and denounce slavery

00:07:40.204 --> 00:07:43.454
"'the great sin and shame of America'!"

00:07:43.454 --> 00:07:44.731
Well, I'm gonna go out on a limb here

00:07:44.731 --> 00:07:48.842
and say that Douglass does not agree

00:07:48.842 --> 00:07:50.599
with Hammond.

00:07:50.599 --> 00:07:54.709
So I think these two
quotes are pretty much

00:07:54.709 --> 00:07:56.869
diametrically opposed.

00:07:56.869 --> 00:08:00.236
So where Hammond says that God entrusted

00:08:00.236 --> 00:08:02.743
enslaved people to his care,

00:08:02.743 --> 00:08:05.390
Douglass is saying he's standing with God

00:08:05.390 --> 00:08:09.686
and the crushed Bible to say that slavery

00:08:09.686 --> 00:08:14.185
is condemned by Christianity.

00:08:21.853 --> 00:08:23.038
What else is he saying?

00:08:23.038 --> 00:08:25.360
Well, he's saying liberty
and the constitution

00:08:25.360 --> 00:08:27.078
are being trampled upon,

00:08:27.078 --> 00:08:31.219
so that there's a
patriotic appeal maybe also

00:08:31.219 --> 00:08:35.623
for why the Declaration of Independence

00:08:35.623 --> 00:08:38.672
and the idea of all men are created equal

00:08:38.672 --> 00:08:41.458
is not compatible with slavery.

00:08:41.458 --> 00:08:43.223
So while Hammond is saying

00:08:43.223 --> 00:08:46.218
oh, I think that all people who own slaves

00:08:46.218 --> 00:08:48.726
desire to treat them kindly

00:08:48.726 --> 00:08:51.582
and God has entrusted us with slaves,

00:08:51.582 --> 00:08:54.747
this is the natural order
meant by the Almighty.

00:08:54.747 --> 00:08:56.001
Douglass is saying,

00:08:56.001 --> 00:08:59.228
no, this is the great
sin and shame of America.

00:08:59.228 --> 00:09:02.572
It is not a Christian
institution and it is not

00:09:02.572 --> 00:09:04.592
an institution which is compatible

00:09:04.592 --> 00:09:06.682
with the ideals of the United States.

00:09:06.682 --> 00:09:08.911
So we've got a ton of information

00:09:08.911 --> 00:09:10.281
out of these documents

00:09:10.281 --> 00:09:11.373
and we haven't even looked at

00:09:11.373 --> 00:09:13.323
a multiple choice question yet.

00:09:13.323 --> 00:09:15.041
All right, are you ready to take some on?

00:09:15.041 --> 00:09:16.899
Let's do it.

00:09:16.899 --> 00:09:20.080
All right, this is an
actual AP practice question,

00:09:20.080 --> 00:09:21.868
and the first thing you want to do

00:09:21.868 --> 00:09:23.749
when you're approaching
one of these questions

00:09:23.749 --> 00:09:26.512
is to read it really carefully.

00:09:26.512 --> 00:09:29.414
So the excerpt from James Henry Hammond

00:09:29.414 --> 00:09:33.037
is most clearly an example
of which of the following

00:09:33.037 --> 00:09:35.753
developments in the mid-19th century?

00:09:35.753 --> 00:09:39.376
All right, so we're
only looking at Hammond.

00:09:39.376 --> 00:09:41.117
And we're specifically thinking about

00:09:41.117 --> 00:09:42.603
the mid-19th century,

00:09:42.603 --> 00:09:44.972
so put ourselves there in time,

00:09:44.972 --> 00:09:46.945
that kind of 1850s era.

00:09:46.945 --> 00:09:49.453
Let's go through the
possible answers one by one,

00:09:49.453 --> 00:09:50.939
and if we don't like something,

00:09:50.939 --> 00:09:53.215
we will cross it out right away.

00:09:53.215 --> 00:09:54.538
All right, option A.

00:09:54.538 --> 00:09:56.953
The decline of slavery in Southern states

00:09:56.953 --> 00:10:00.320
as a result of gradual emancipation laws.

00:10:00.320 --> 00:10:05.095
All right, so says that
slavery was declining

00:10:05.095 --> 00:10:08.087
as a result of gradual emancipation laws.

00:10:08.087 --> 00:10:09.735
Well, I don't think
that can be true, right?

00:10:09.735 --> 00:10:10.618
Because if anything,

00:10:10.618 --> 00:10:13.240
slavery's getting stronger
before the Civil War.

00:10:13.240 --> 00:10:15.957
I don't remember any
gradual emancipation laws

00:10:15.957 --> 00:10:17.071
in the South.

00:10:17.071 --> 00:10:19.693
So let's get rid of that.

00:10:19.693 --> 00:10:21.039
All right, option B.

00:10:21.039 --> 00:10:23.872
The increasingly restrictive
nature of slavery

00:10:23.872 --> 00:10:27.587
in the South enforced
by stronger slave codes.

00:10:27.587 --> 00:10:30.095
Well, there certainly
were more slave codes

00:10:30.095 --> 00:10:33.207
in the 1850s and they
were pretty restrictive,

00:10:33.207 --> 00:10:36.341
but is that what the
excerpt is talking about?

00:10:36.341 --> 00:10:38.808
No, he's talking about kindness

00:10:38.808 --> 00:10:42.198
and that slave owners should
treat their slaves kindly,

00:10:42.198 --> 00:10:44.288
so that's probably not the right one,

00:10:44.288 --> 00:10:46.122
but let's leave it on the table for now

00:10:46.122 --> 00:10:48.351
just in case there's not a better answer.

00:10:48.351 --> 00:10:50.720
The expanding use of moral arguments

00:10:50.720 --> 00:10:53.460
by Northern anti-slavery activists.

00:10:53.460 --> 00:10:55.062
Well, Hammond is a Southerner,

00:10:55.062 --> 00:10:58.452
so I'm gonna go with no.

00:10:59.532 --> 00:11:01.112
All right, option D.

00:11:01.112 --> 00:11:03.898
The growing tendency among
Southern slaveholders

00:11:03.898 --> 00:11:06.569
to justify slavery as a positive good.

00:11:06.569 --> 00:11:08.473
Yeah, I think that's
actually the best option.

00:11:08.473 --> 00:11:09.239
Right?

00:11:09.239 --> 00:11:11.607
Because he's saying God intended this,

00:11:11.607 --> 00:11:14.162
we're trying to treat them with kindness.

00:11:14.162 --> 00:11:16.902
So it's a very pro-slavery argument

00:11:16.902 --> 00:11:21.499
made on the grounds that
slavery is a good institution.

00:11:21.499 --> 00:11:25.122
Now it's worth noting
that one of these options,

00:11:25.122 --> 00:11:27.931
option B, what it says is true.

00:11:27.931 --> 00:11:31.391
But it's not a clear
example of what Hammond

00:11:31.391 --> 00:11:33.086
is saying in the excerpt,

00:11:33.086 --> 00:11:35.733
so make sure that you're
answering the question

00:11:35.733 --> 00:11:37.985
that you're actually being asked,

00:11:37.985 --> 00:11:41.399
not just looking for what
could be factually true

00:11:41.399 --> 00:11:43.790
among the answers.

00:11:43.790 --> 00:11:45.718
All right, I think this
is enough for this video,

00:11:45.718 --> 00:11:47.273
but stay tuned to the next video

00:11:47.273 --> 00:11:49.711
and we'll do a few more examples.


The future tense

WEBVTT
Kind: captions
Language: en

00:00:00.700 --> 00:00:01.673
- [Voiceover] Hello, grammar pals,

00:00:01.673 --> 00:00:03.137
and welcome to the future,

00:00:03.137 --> 00:00:07.119
full of jet packs and
spaceships and shiny jumpsuits,

00:00:07.119 --> 00:00:09.286
and also the word "will"!

00:00:11.960 --> 00:00:14.330
There's a lot of will in the future,

00:00:14.330 --> 00:00:18.357
by which I mean we use this word, "will",

00:00:18.357 --> 00:00:20.881
to form the future tense in English.

00:00:20.881 --> 00:00:23.402
So, in the present tense you'd say,

00:00:23.402 --> 00:00:25.235
"I eat this cupcake."

00:00:32.620 --> 00:00:34.286
That's the present.

00:00:35.853 --> 00:00:38.519
But in the future, you would say

00:00:40.761 --> 00:00:43.011
"I will eat this cupcake."

00:00:44.992 --> 00:00:47.592
Because we use the future

00:00:47.592 --> 00:00:52.228
to talk about stuff that's
happening later than now.

00:00:52.228 --> 00:00:56.062
Literally, it's in the
future, so it's later,

00:00:56.986 --> 00:00:57.819
as opposed to the present,

00:00:57.819 --> 00:00:59.881
which talks about now, and the past

00:00:59.881 --> 00:01:01.263
which talks about stuff

00:01:01.263 --> 00:01:04.354
that has already happened,
happened earlier.

00:01:04.354 --> 00:01:07.326
So the most common way to form the future

00:01:07.326 --> 00:01:10.173
is to just make a sentence
in the present tense

00:01:10.173 --> 00:01:14.340
and then before the verb,
just stick "will" in there.

00:01:15.260 --> 00:01:17.677
So, "I pet the triceratops."

00:01:25.533 --> 00:01:28.033
Everyone's favorite dinosaur.

00:01:33.862 --> 00:01:35.245
Wish I could pet one.

00:01:35.245 --> 00:01:37.245
Can't, they're extinct.

00:01:40.284 --> 00:01:42.112
"I pet the triceratops."

00:01:42.112 --> 00:01:47.076
But in the future, maybe
when they clone dinosaurs,

00:01:47.076 --> 00:01:49.576
"I will pet the triceratops."

00:01:54.937 --> 00:01:57.104
And we will be best buds.

00:02:00.554 --> 00:02:03.644
So that's the most basic
way of forming the future.

00:02:03.644 --> 00:02:06.311
You can also use "is going to".

00:02:10.027 --> 00:02:11.527
So you could say,

00:02:12.960 --> 00:02:16.043
"Lorraine is going to visit Canada."

00:02:27.503 --> 00:02:29.525
And that's another way to form the future.

00:02:29.525 --> 00:02:31.463
But the most common way to do it

00:02:31.463 --> 00:02:33.945
is to just put in "will".

00:02:33.945 --> 00:02:36.829
Just write the sentence as you
would for the present tense,

00:02:36.829 --> 00:02:40.211
but then you just gotta pop in "will".

00:02:40.211 --> 00:02:41.923
"I eat this cupcake." is the present,

00:02:41.923 --> 00:02:45.254
"I will eat this cupcake." In the future.

00:02:45.254 --> 00:02:46.391
That's the future tense.

00:02:46.391 --> 00:02:48.629
You will be able to learn anything.

00:02:48.629 --> 00:02:49.594
David, out.


The past tense

WEBVTT
Kind: captions
Language: en

00:00:00.665 --> 00:00:02.047
- [Voiceover] Hello, friends,

00:00:02.047 --> 00:00:04.446
and welcome to the distant past,

00:00:04.446 --> 00:00:07.046
because today we're talking
about the past tense,

00:00:07.046 --> 00:00:10.792
which refers to stuff
that has already happened.

00:00:10.792 --> 00:00:12.660
There are many ways to
form the past tense,

00:00:12.660 --> 00:00:16.242
but for now I just wanna
focus on the basic version,

00:00:16.242 --> 00:00:18.763
which is just adding "-ed".

00:00:18.763 --> 00:00:21.513
So if you take a word like "walk"

00:00:23.520 --> 00:00:26.020
as in, "I walk to the store,"

00:00:27.688 --> 00:00:30.893
no, not the store, to the moon.

00:00:30.893 --> 00:00:33.135
I'm going to the moon on foot,

00:00:33.135 --> 00:00:34.551
try and stop me.

00:00:35.857 --> 00:00:37.078
That's in the present tense,

00:00:37.078 --> 00:00:38.499
but if I wanted to put that in the past,

00:00:38.499 --> 00:00:41.583
I would say, "I walked to the moon."

00:00:48.181 --> 00:00:51.234
I've got very strong legs and good shoes.

00:00:51.234 --> 00:00:54.691
So this sentence is happening now.

00:00:54.691 --> 00:00:56.191
It's the present.

00:00:59.052 --> 00:01:01.719
This sentence happened earlier.

00:01:04.265 --> 00:01:05.515
It's the past.

00:01:06.423 --> 00:01:08.133
SO, the simplest way to figure out

00:01:08.133 --> 00:01:10.408
whether or not something
is in the past tense

00:01:10.408 --> 00:01:13.989
or if you want to put
something in the past tense,

00:01:13.989 --> 00:01:17.238
is this thing, this "ed" ending.

00:01:17.238 --> 00:01:20.155
So you go from "walk" to "walked",

00:01:21.139 --> 00:01:24.722
"talk" to "talked", "sneeze" to "sneezed",

00:01:30.551 --> 00:01:33.968
"jump" to "jumped" and "open" to "opened"

00:01:37.874 --> 00:01:41.692
So, if it doesn't end with
with an "e", you add an "ed".

00:01:41.692 --> 00:01:43.195
If it does end with an "e",

00:01:43.195 --> 00:01:45.715
you just add the "d".

00:01:45.715 --> 00:01:47.099
That's how to form the past tense.

00:01:47.099 --> 00:01:48.643
That's what the past tense does.

00:01:48.643 --> 00:01:50.351
It's stuff that's already happened,

00:01:50.351 --> 00:01:52.549
and most of the time when you wanna form

00:01:52.549 --> 00:01:54.508
the past tense out of a word,

00:01:54.508 --> 00:01:56.091
you just add "ed".

00:01:57.026 --> 00:01:58.025
You can learn anything.

00:01:58.025 --> 00:01:58.859
David, out.


The present tense

WEBVTT
Kind: captions
Language: en

00:00:00.582 --> 00:00:01.415
- [Voiceover] Hello, grammarians!

00:00:01.415 --> 00:00:02.653
Welcome to the present tense,

00:00:02.653 --> 00:00:05.820
or that which is happening right now.

00:00:07.755 --> 00:00:09.954
The present tense is how we talk about

00:00:09.954 --> 00:00:12.810
things that are happening
in the present moment.

00:00:12.810 --> 00:00:14.727
Like, "I eat a donut."

00:00:16.972 --> 00:00:19.536
If I say it that way, it means

00:00:19.536 --> 00:00:22.707
it's happening right now in the present

00:00:22.707 --> 00:00:25.229
as opposed to happening
later, in the future,

00:00:25.229 --> 00:00:27.562
or before now, in the past.

00:00:28.929 --> 00:00:32.553
The present tense is
what's happening right now.

00:00:32.553 --> 00:00:35.234
If you can just imagine,

00:00:35.234 --> 00:00:39.438
just put the words "right now" at the end

00:00:39.438 --> 00:00:42.443
of anything that takes
place in the present.

00:00:42.443 --> 00:00:45.358
"I eat a donut right now."

00:00:45.358 --> 00:00:48.941
"Louise doesn't want
a catapult right now."

00:00:50.109 --> 00:00:53.109
"The water is super cold right now."

00:00:56.096 --> 00:00:59.352
"Bertie is singing in
the shower right now."

00:00:59.352 --> 00:01:01.585
All of these sentences are taking place

00:01:01.585 --> 00:01:03.575
in what we call the present.

00:01:03.575 --> 00:01:05.899
There are a couple of ways
to form the present tense,

00:01:05.899 --> 00:01:07.772
and I demonstrated two of them here.

00:01:07.772 --> 00:01:12.088
So we can say "eat" or "doesn't" or "is".

00:01:12.088 --> 00:01:14.771
We can also say "is singing".

00:01:14.771 --> 00:01:18.142
So when you generally have something

00:01:18.142 --> 00:01:20.726
that has "is" and "ing" in it,

00:01:22.181 --> 00:01:24.166
means it's happening right now.

00:01:24.166 --> 00:01:25.959
It's happening in the present tense.

00:01:25.959 --> 00:01:29.455
So yeah, those are two of
the ways to form the present.

00:01:29.455 --> 00:01:31.935
If the verb is kind of unadorned,

00:01:31.935 --> 00:01:34.443
if it's kind of plain, "I eat a donut.",

00:01:34.443 --> 00:01:36.840
not "I was eating a donut."

00:01:36.840 --> 00:01:37.815
or "I ate a donut."

00:01:37.815 --> 00:01:40.171
or "I will eat a donut."

00:01:40.171 --> 00:01:42.139
if it's just kind of on its own like this,

00:01:42.139 --> 00:01:44.658
it's probably gonna be
in the present tense.

00:01:44.658 --> 00:01:48.737
Likewise, if you see the
word "is" and then "ing",

00:01:48.737 --> 00:01:52.548
that also means it's in the present tense.

00:01:52.548 --> 00:01:55.190
That's what you gotta know
about the present tense.

00:01:55.190 --> 00:01:56.857
It's happening now.

00:01:58.203 --> 00:01:59.663
You can learn anything.

00:01:59.663 --> 00:02:00.663
David, out.


2015 AP Chemistry free response 1d

WEBVTT
Kind: captions
Language: en

00:00:00.419 --> 00:00:02.823
- [Voiceover] Metal-air
cells need to be lightweight

00:00:02.823 --> 00:00:04.622
for many applications.

00:00:04.622 --> 00:00:08.698
In order to transfer more
electrons with a smaller mass,

00:00:08.698 --> 00:00:11.127
sodium and calcium

00:00:11.127 --> 00:00:14.181
are investigated as potential anodes.

00:00:14.181 --> 00:00:16.967
A 1.0 gram anode

00:00:16.967 --> 00:00:19.277
of anode of which of, (laughs)

00:00:19.277 --> 00:00:22.167
A 1.0 grm anode of which of these metals

00:00:22.167 --> 00:00:24.497
would transfer more electrons,

00:00:24.497 --> 00:00:27.474
assuming that the anode
is totally consumed

00:00:27.474 --> 00:00:30.246
during the lifetime of a cell?

00:00:30.246 --> 00:00:32.963
Justify your answer with calculations.

00:00:32.963 --> 00:00:35.563
So let's go to the top

00:00:35.563 --> 00:00:39.262
where they showed the reactions

00:00:39.262 --> 00:00:41.316
involving sodium and calcium.

00:00:41.316 --> 00:00:42.746
And actually, let me
just copy and paste this

00:00:42.746 --> 00:00:45.986
so it's easier for me to
reference near the bottom,

00:00:45.986 --> 00:00:48.494
where we're actually doing the question.

00:00:48.494 --> 00:00:51.013
So let me just copy this.

00:00:51.013 --> 00:00:54.647
And then let's paste it down here,

00:00:54.647 --> 00:00:57.777
that I can reference it.

00:00:57.777 --> 00:01:00.944
Okay, I'll even make
it a little bit smaller

00:01:00.944 --> 00:01:03.948
just so I don't take up
too much much real estate.

00:01:03.948 --> 00:01:06.498
And so the reactions that we care about

00:01:06.498 --> 00:01:08.534
are actually going to go
in the reverse direction

00:01:08.534 --> 00:01:10.437
of these half-reactions.

00:01:10.437 --> 00:01:13.931
Remember, when we looked
at our power source

00:01:13.931 --> 00:01:15.777
right over here,

00:01:15.777 --> 00:01:17.147
this first half-reaction

00:01:17.147 --> 00:01:19.831
is what produces the hydroxide ions.

00:01:19.831 --> 00:01:23.791
The hydroxide ions migrate
their way to the left-hand side.

00:01:23.791 --> 00:01:25.575
And then they perform,

00:01:25.575 --> 00:01:29.581
then they are involved in oxidizing,

00:01:29.581 --> 00:01:33.123
in oxidizing whatever metal you have here.

00:01:33.123 --> 00:01:34.180
If this was zinc,

00:01:34.180 --> 00:01:36.804
the hydroxide combines with the zinc.

00:01:36.804 --> 00:01:38.429
They're going to oxidize the zinc.

00:01:38.429 --> 00:01:40.124
And those extra electrons

00:01:40.124 --> 00:01:41.669
that are released in that reaction,

00:01:41.669 --> 00:01:44.119
those are the ones that are
going to travel across the wire

00:01:44.119 --> 00:01:45.778
and provide the current.

00:01:45.778 --> 00:01:46.986
But the hydroxide,

00:01:46.986 --> 00:01:48.449
it could react with sodium,

00:01:48.449 --> 00:01:49.749
if this metal is sodium.

00:01:49.749 --> 00:01:51.247
It could react with calcium,

00:01:51.247 --> 00:01:52.268
if this metal is calcium.

00:01:52.268 --> 00:01:53.580
So the reactions we care about

00:01:53.580 --> 00:01:56.738
are going from this side, the right side,

00:01:56.738 --> 00:01:58.944
to the left side.

00:01:58.944 --> 00:02:01.603
And so, let me just rewrite that again.

00:02:01.603 --> 00:02:03.671
And actually, just the act
of rewriting it will help,

00:02:03.671 --> 00:02:04.367
will,

00:02:04.367 --> 00:02:06.352
my pen has been having trouble,

00:02:06.352 --> 00:02:07.714
is having trouble,

00:02:07.714 --> 00:02:09.153
actually scrolling down.

00:02:09.153 --> 00:02:10.314
But just the act of rewriting it

00:02:10.314 --> 00:02:13.878
will help with digesting what's going on.

00:02:13.878 --> 00:02:15.772
So the sodium reaction.

00:02:15.772 --> 00:02:19.395
For every two molecules of sodium,

00:02:19.395 --> 00:02:20.114
it's solid,

00:02:20.114 --> 00:02:21.937
it's actually forming our anode,

00:02:21.937 --> 00:02:25.657
plus two molecules of hydroxide,

00:02:26.537 --> 00:02:29.067
dissolved in the water, aqueous solution,

00:02:29.067 --> 00:02:31.883
we are going to yield

00:02:31.883 --> 00:02:36.845
sodium oxide,

00:02:36.845 --> 00:02:39.218
a solid version of that,

00:02:39.218 --> 00:02:43.559
plus water in the liquid state,

00:02:43.559 --> 00:02:45.404
and plus two electrons.

00:02:45.404 --> 00:02:46.326
And this is really important

00:02:46.326 --> 00:02:47.477
'cause we wanna think

00:02:47.477 --> 00:02:50.663
about one gram of each of these metals.

00:02:50.663 --> 00:02:53.367
How many electrons would they yield?

00:02:53.367 --> 00:02:54.144
How many electrons

00:02:54.144 --> 00:02:58.393
are they going to be
able to transfer through,

00:02:58.393 --> 00:02:59.426
potentially through,

00:02:59.426 --> 00:03:00.285
that wire?

00:03:00.285 --> 00:03:02.302
So that's the first relationship up there.

00:03:02.302 --> 00:03:04.346
And then, actually, let me
just leave the sodium there.

00:03:04.346 --> 00:03:06.308
And then let me do the calcium over here.

00:03:06.308 --> 00:03:07.945
And remember, we wanna go
from the right to the left,

00:03:07.945 --> 00:03:09.685
so let me rewrite it that way.

00:03:09.685 --> 00:03:12.599
Calcium, a solid state,

00:03:12.599 --> 00:03:16.179
plus two hydroxides,

00:03:16.179 --> 00:03:18.617
dissolved in water,

00:03:18.617 --> 00:03:23.617
is going to yield calcium oxide, solid,

00:03:23.631 --> 00:03:27.046
plus liquid water, liquid,

00:03:27.046 --> 00:03:30.308
plus two electrons.

00:03:30.308 --> 00:03:30.833
So, once again,

00:03:30.833 --> 00:03:33.345
I just rewrote each of these
in the opposite direction.

00:03:33.345 --> 00:03:35.143
And, if I wanna write the voltage,

00:03:35.143 --> 00:03:36.443
I would flip the sign now,

00:03:36.443 --> 00:03:39.183
'cause I have written them
in the other direction.

00:03:39.183 --> 00:03:40.681
But they're not asking
us about the voltage.

00:03:40.681 --> 00:03:43.361
They want us to know a one gram anode

00:03:43.361 --> 00:03:44.317
of which of these metals

00:03:44.317 --> 00:03:46.358
would transfer more electrons?

00:03:46.358 --> 00:03:48.484
So if we think about sodium,

00:03:48.484 --> 00:03:50.503
the case with sodium,

00:03:50.503 --> 00:03:53.569
we have 1.0 grams,

00:03:53.569 --> 00:03:58.234
1.0 grams of sodium.

00:03:58.234 --> 00:04:02.640
Well, let's think about how
many moles of sodium that is.

00:04:02.640 --> 00:04:04.426
Well, that's going to be,

00:04:04.426 --> 00:04:05.228
well let's see.

00:04:05.228 --> 00:04:06.701
We're going to have,

00:04:06.701 --> 00:04:09.581
we could look up sodium

00:04:09.581 --> 00:04:11.452
on our Periodic Table of Elements.

00:04:11.452 --> 00:04:12.232
And this is actually the one

00:04:12.232 --> 00:04:15.240
that they give you when
you take the AP Test.

00:04:15.240 --> 00:04:17.620
And you see sodium right over here.

00:04:17.620 --> 00:04:19.477
We could read its atomic weight,

00:04:19.477 --> 00:04:21.915
sometimes now called relative atomic mass.

00:04:21.915 --> 00:04:22.966
And that's the weighted average

00:04:22.966 --> 00:04:25.190
of the atomic masses of the isotopes

00:04:25.190 --> 00:04:27.129
that you would typically
find of sodium on Earth,

00:04:27.129 --> 00:04:28.750
if you just took a
random sample of sodium,

00:04:28.750 --> 00:04:30.691
and you were, average their atomic masses,

00:04:30.691 --> 00:04:33.362
it would be 22.99.

00:04:33.362 --> 00:04:35.382
So that tells us that a mole of sodium

00:04:35.382 --> 00:04:36.293
is going to weigh,

00:04:36.293 --> 00:04:40.521
is going to have a mass of 22.99 grams.

00:04:41.611 --> 00:04:44.391
Or you could say,

00:04:44.391 --> 00:04:47.840
so a mole is going to,

00:04:47.840 --> 00:04:51.974
a mole is going to have
a mass of 22.99 grams.

00:04:51.974 --> 00:04:54.871
So I could write one mole,

00:04:54.871 --> 00:04:57.650
one mole of sodium

00:04:57.650 --> 00:05:00.094
is going to have a mass

00:05:00.094 --> 00:05:04.436
of 22.99 grams.

00:05:04.436 --> 00:05:06.758
And of course, this is
still talking about sodium.

00:05:06.758 --> 00:05:07.951
And so I made sure

00:05:07.951 --> 00:05:10.483
that I have it in terms of moles per gram,

00:05:10.483 --> 00:05:12.201
because when you do our
dimensional analysis,

00:05:12.201 --> 00:05:13.934
grams divided by grams,

00:05:13.934 --> 00:05:15.783
or grams of sodium divided
by grams of sodium,

00:05:15.783 --> 00:05:16.758
they're gonna cancel out,

00:05:16.758 --> 00:05:18.779
and I'm gonna be left
with moles of sodium.

00:05:18.779 --> 00:05:20.088
So this part of the expression,

00:05:20.088 --> 00:05:21.169
this is gonna give me

00:05:21.169 --> 00:05:23.735
how many moles of sodium
we are dealing with

00:05:23.735 --> 00:05:25.988
if I have one gram of sodium.

00:05:25.988 --> 00:05:29.169
But we need to think
about how many electrons,

00:05:29.169 --> 00:05:30.490
how many electrons

00:05:30.490 --> 00:05:34.410
are we going to be able to transfer?

00:05:34.410 --> 00:05:36.978
And that's where we actually
have to look at this reaction.

00:05:36.978 --> 00:05:38.992
So for every two,

00:05:38.992 --> 00:05:42.811
for every two moles of sodium,

00:05:42.811 --> 00:05:47.202
we are going to transfer
two moles of electrons.

00:05:47.202 --> 00:05:48.721
Or another way you can think about it is

00:05:48.721 --> 00:05:50.114
for every mole that,

00:05:50.114 --> 00:05:51.832
here you have a two to two relationship,

00:05:51.832 --> 00:05:53.988
or you could say for every mole of sodium,

00:05:53.988 --> 00:05:56.949
we are going to transfer
one mole of electrons.

00:05:56.949 --> 00:05:58.109
And so let's do that.

00:05:58.109 --> 00:06:01.986
We're gonna transfer one mole,

00:06:01.986 --> 00:06:03.796
one mole of,

00:06:03.796 --> 00:06:06.002
let me write it this way.

00:06:06.002 --> 00:06:10.382
One mole of electrons

00:06:10.382 --> 00:06:15.382
per mole of sodium.

00:06:15.492 --> 00:06:16.993
If you have two moles of sodium,

00:06:16.993 --> 00:06:18.804
you're going to get
two moles of electrons.

00:06:18.804 --> 00:06:19.710
If you have one mole of sodium,

00:06:19.710 --> 00:06:21.045
you're gonna have two. (laughs)

00:06:21.045 --> 00:06:21.834
If you have one mole of sodium,

00:06:21.834 --> 00:06:24.227
you're gonna have one mole of electrons.

00:06:24.227 --> 00:06:26.108
And so, what is this going to give us?

00:06:26.108 --> 00:06:28.266
Well, if you just multiply out.

00:06:28.266 --> 00:06:29.736
Actually, let's look at the units first.

00:06:29.736 --> 00:06:32.616
Grams of sodium cancel
out with grams of sodium.

00:06:32.616 --> 00:06:35.344
Moles of sodium cancel
out with moles of sodium.

00:06:35.344 --> 00:06:38.878
And so you're left with
just moles of electrons,

00:06:38.878 --> 00:06:41.382
moles of, (scoffs)

00:06:41.382 --> 00:06:43.123
why am I making an apostrophe?

00:06:43.123 --> 00:06:44.342
Moles of electrons.

00:06:44.342 --> 00:06:46.983
And it's going to be 1.0 times one,

00:06:46.983 --> 00:06:49.944
divided by 22.9, times one.

00:06:49.944 --> 00:06:52.393
So it's 1.0 divided by 22.9.

00:06:52.393 --> 00:06:53.172
And let's see.

00:06:53.172 --> 00:06:56.169
I'm gonna have two significant
digits right over here,

00:06:56.169 --> 00:06:57.665
two significant figures.

00:06:57.665 --> 00:07:00.591
So let me get the calculator out.

00:07:00.591 --> 00:07:02.772
And it is, let's see,

00:07:02.772 --> 00:07:04.072
so it's just one,

00:07:04.072 --> 00:07:08.829
I could just say one divided by 22.9

00:07:08.829 --> 00:07:10.539
is equal to,

00:07:10.539 --> 00:07:12.837
so if we have two significant figures,

00:07:12.837 --> 00:07:17.820
it's approximately .044,

00:07:17.820 --> 00:07:20.590
.044

00:07:20.590 --> 00:07:23.425
So, I'll say approximately

00:07:23.425 --> 00:07:28.012
0.044 moles of electron.

00:07:28.012 --> 00:07:28.763
Remember, moles.

00:07:28.763 --> 00:07:29.443
All we've got is numbers.

00:07:29.443 --> 00:07:31.147
This is still a lot of electrons.

00:07:31.147 --> 00:07:33.097
A mole is 6.022 times 10 to the,

00:07:33.097 --> 00:07:34.323
you know, or roughly that,

00:07:34.323 --> 00:07:35.301
times 10 to the 23rd.

00:07:35.301 --> 00:07:37.844
So it's a very, very
large number of electrons

00:07:37.844 --> 00:07:40.468
that we are going to
potentially transfer over here,

00:07:40.468 --> 00:07:42.325
if we have one gram of sodium.

00:07:42.325 --> 00:07:44.891
Now let's do the same
thing with the calcium.

00:07:44.891 --> 00:07:46.644
So if we have calcium,

00:07:46.644 --> 00:07:48.804
it's going to be the same exercise here.

00:07:48.804 --> 00:07:53.193
We have one gram of calcium

00:07:53.193 --> 00:07:57.413
times one mole of calcium,

00:07:57.413 --> 00:07:59.233
has what mass?

00:07:59.233 --> 00:08:01.335
One mole of calcium has a mass

00:08:01.335 --> 00:08:05.459
of how many grams?

00:08:05.459 --> 00:08:07.894
So let's go back to the Periodic Table.

00:08:07.894 --> 00:08:10.905
And there you have
calcium right over here.

00:08:10.905 --> 00:08:13.784
The atomic weight is 40.08,

00:08:13.784 --> 00:08:15.912
or oftentimes, or now the more modern name

00:08:15.912 --> 00:08:17.042
is relative atomic mass,

00:08:17.042 --> 00:08:18.755
the weighted average of the typical,

00:08:18.755 --> 00:08:19.877
of the isotopes.

00:08:19.877 --> 00:08:21.491
40.08.

00:08:21.491 --> 00:08:25.439
So I could write 40.08

00:08:25.439 --> 00:08:26.719
right over here.

00:08:26.719 --> 00:08:28.438
And then, in our reaction,

00:08:28.438 --> 00:08:30.737
for every mole of calcium,

00:08:30.737 --> 00:08:34.961
how many moles of electrons
are we going to generate?

00:08:34.961 --> 00:08:36.361
Well, we have in this reaction,

00:08:36.361 --> 00:08:37.962
one, for every one calcium,

00:08:37.962 --> 00:08:39.321
we have two electrons.

00:08:39.321 --> 00:08:40.343
So for every mole of calcium,

00:08:40.343 --> 00:08:43.210
we're gonna have two moles of electrons.

00:08:43.210 --> 00:08:43.900
So we could say

00:08:43.900 --> 00:08:48.020
times two moles of electrons

00:08:48.020 --> 00:08:51.467
for every mole of calcium

00:08:51.467 --> 00:08:54.640
that we have as a reactant over here.

00:08:54.640 --> 00:08:57.204
And so this is going to give us,

00:08:57.204 --> 00:08:59.341
this is going to be approximately,

00:08:59.341 --> 00:09:00.966
see, our units,

00:09:00.966 --> 00:09:03.718
grams of calcium cancels
with grams of calcium.

00:09:03.718 --> 00:09:07.112
Moles of calcium cancel
with moles of calcium.

00:09:07.112 --> 00:09:09.343
And so we're gonna have one times one,

00:09:09.343 --> 00:09:11.445
divided by 40.08, times two.

00:09:11.445 --> 00:09:14.509
So it's going to be two divided by 40.08,

00:09:14.509 --> 00:09:18.687
which is, so, two

00:09:18.687 --> 00:09:23.687
divided by 40.08.

00:09:23.772 --> 00:09:25.896
Now we're gonna have
two significant figures

00:09:25.896 --> 00:09:27.060
right over here.

00:09:27.060 --> 00:09:28.083
'Cause this two and those ones

00:09:28.083 --> 00:09:29.720
are kind of pure numbers,

00:09:29.720 --> 00:09:31.438
while these are from measurements.

00:09:31.438 --> 00:09:34.031
So, and this is the fewest
number of significant figures,

00:09:34.031 --> 00:09:35.504
so we have two.

00:09:35.504 --> 00:09:37.679
So two divided by that.

00:09:37.679 --> 00:09:41.771
Let's see, so it's gonna be 0.050.

00:09:42.791 --> 00:09:47.726
So 0.050

00:09:47.726 --> 00:09:50.838
moles of electrons.

00:09:50.838 --> 00:09:51.721
So you can see,

00:09:51.721 --> 00:09:54.322
right from this calculation,

00:09:54.322 --> 00:09:56.978
that one gram of calcium

00:09:57.978 --> 00:10:02.468
can transfer more electrons

00:10:02.468 --> 00:10:03.966
than one gram of sodium,

00:10:03.966 --> 00:10:05.695
if sodium was the anode.

00:10:05.695 --> 00:10:09.306
So we see very clearly that calcium,

00:10:09.306 --> 00:10:11.942
so one gram of calcium

00:10:11.942 --> 00:10:15.998
can transfer more electrons,

00:10:15.998 --> 00:10:20.998
can transfer more electrons,

00:10:21.173 --> 00:10:24.550
more electrons than,

00:10:26.070 --> 00:10:29.600
1.0 gram

00:10:29.600 --> 00:10:31.253
of sodium.

00:10:31.253 --> 00:10:32.925
And you can see it right over here.

00:10:32.925 --> 00:10:37.336
We have done the calculation.


2015 AP Chemistry free response 1e

WEBVTT
Kind: captions
Language: en

00:00:00.143 --> 00:00:02.256
- [Voiceover] The only
common oxide of zinc

00:00:02.256 --> 00:00:06.846
has a formula ZnO, zinc and
then you have your oxygen.

00:00:06.846 --> 00:00:10.491
Write the electron
configuration for a zinc atom

00:00:10.491 --> 00:00:13.092
in the ground state.

00:00:13.092 --> 00:00:15.437
So there's a couple of
ways that you could do this

00:00:15.437 --> 00:00:17.039
for the electron configuration.

00:00:17.039 --> 00:00:20.871
Let's first identify zinc on
our periodic table of elements,

00:00:20.871 --> 00:00:22.937
and this is the actual one
that they will give you

00:00:22.937 --> 00:00:24.679
when you take the AP test.

00:00:24.679 --> 00:00:27.906
And so we have zinc right over here,

00:00:27.906 --> 00:00:30.042
zinc right over there,
and there's a couple

00:00:30.042 --> 00:00:30.994
of ways you could do it.

00:00:30.994 --> 00:00:33.325
The simplest way is starting with the

00:00:35.605 --> 00:00:39.205
noble gas that is before zinc,

00:00:39.205 --> 00:00:41.527
so that would be argon right over here.

00:00:41.527 --> 00:00:42.786
You could say it's going to have the same

00:00:42.786 --> 00:00:47.786
electron configuration as argon, argon.

00:00:48.149 --> 00:00:49.218
Let me...

00:00:49.218 --> 00:00:51.447
So you're gonna have argon
but then you're going to go

00:00:51.447 --> 00:00:53.027
and you're gonna add the four,

00:00:53.027 --> 00:00:55.580
you're gonna add electrons
to the 4s subshell.

00:00:55.580 --> 00:00:58.204
So you'll go 4s1, 4s2.

00:00:58.204 --> 00:01:02.174
So argon and then you have 4s2,

00:01:02.174 --> 00:01:03.893
and then you go and--

00:01:03.893 --> 00:01:06.400
it's an oversimplification
what I'm about to say,

00:01:06.400 --> 00:01:08.095
but when you're figuring
out electron configurations,

00:01:08.095 --> 00:01:10.766
it's helpful to think of
well, after you figure out

00:01:10.766 --> 00:01:14.318
fill in the s subshell,
then you go and backfill

00:01:14.318 --> 00:01:16.524
the 3d subshell.

00:01:16.524 --> 00:01:21.524
So 3d1, 3d2, 3d3, 3d4, 5, 6, 7, 8, 9, 10.

00:01:22.608 --> 00:01:27.608
So 4s2 3d10.

00:01:28.575 --> 00:01:32.198
And there's two exceptions
in this fourth row here.

00:01:32.198 --> 00:01:35.820
You have the exceptions
of chromium and copper

00:01:35.820 --> 00:01:38.091
that don't exactly fill just like that.

00:01:38.091 --> 00:01:39.744
You can look those up on your own,

00:01:39.744 --> 00:01:42.159
but that right over here is
the electron configuration

00:01:42.159 --> 00:01:45.340
for a zinc atom in the ground state.

00:01:45.340 --> 00:01:46.989
Now another way you could write this

00:01:46.989 --> 00:01:49.467
is actually writing out
the electron configuration

00:01:49.467 --> 00:01:52.811
for argon and then writing 4s2 3d10,

00:01:52.811 --> 00:01:55.737
and we'll just for the
sake of it, let's do that.

00:01:55.737 --> 00:02:00.506
So you fill up your 1s2.

00:02:00.506 --> 00:02:04.147
So we go 1s2,

00:02:04.147 --> 00:02:06.453
and then we're in the second row,

00:02:06.453 --> 00:02:09.611
so you're gonna have 2s2 and then 2

00:02:09.611 --> 00:02:12.513
one, two, three, four, five, six, 2p6.

00:02:12.513 --> 00:02:15.625
2s2 2p6.

00:02:15.625 --> 00:02:17.297
So let me write that down.

00:02:17.297 --> 00:02:22.297
2s2 2p6.

00:02:23.032 --> 00:02:25.867
And then you're going
to go to the third row,

00:02:25.867 --> 00:02:26.910
so you're gonna have--

00:02:26.910 --> 00:02:28.117
and if this looks
completely foreign to you,

00:02:28.117 --> 00:02:29.998
I encourage you to watch
the Khan Academy videos

00:02:29.998 --> 00:02:31.623
on electron configuration.

00:02:31.623 --> 00:02:36.291
And then you're gonna have 3s2 3p6.

00:02:36.291 --> 00:02:38.589
You're gonna fill those
two subshells next.

00:02:38.589 --> 00:02:43.589
3s2 3p6, and then what
we've just described

00:02:44.742 --> 00:02:47.293
is essentially the electron
configuration of argon,

00:02:47.293 --> 00:02:50.753
and so then you get to 4s2 and 3d10.

00:02:50.753 --> 00:02:55.753
4s2 and 3d10.

00:02:57.347 --> 00:03:02.347
So either of those would do,
and then the second part.

00:03:02.456 --> 00:03:06.171
From which sublevel are electrons
removed when a zinc atom

00:03:06.171 --> 00:03:09.004
in the ground state is oxidized?

00:03:09.004 --> 00:03:11.419
And this is what's interesting
about d block elements,

00:03:11.419 --> 00:03:13.207
and that's why I said
it's a little more nuanced

00:03:13.207 --> 00:03:15.807
than saying you're kind of
constructing this electron

00:03:15.807 --> 00:03:18.013
by electron and you fill these in,

00:03:18.013 --> 00:03:21.008
the 4s2 and then you
go and backfill the 3d

00:03:21.008 --> 00:03:23.702
because it actually
turns out when you have

00:03:23.702 --> 00:03:27.487
a neutral zinc atom, the
highest energy electrons,

00:03:27.487 --> 00:03:30.087
the ones that are the most
likely to be pulled away

00:03:30.087 --> 00:03:33.872
from the zinc atom are
not the d electrons.

00:03:33.872 --> 00:03:38.261
It's actually going to
be the 4s2 electrons.

00:03:38.261 --> 00:03:43.021
So from which sublevel
are electrons removed?

00:03:43.021 --> 00:03:45.877
Well, the most likely to
be removed not the first to

00:03:45.877 --> 00:03:47.827
is going to be the 4s electrons.

00:03:47.827 --> 00:03:52.827
So the 4s sublevel.

00:03:54.050 --> 00:03:56.233
And once again, I encourage
you to kinda read more

00:03:56.233 --> 00:03:58.485
about that if you're
curious about why that is.

00:03:58.485 --> 00:04:00.227
You can kind of imagine in your head.

00:04:00.227 --> 00:04:02.085
Even when you look at energy levels,

00:04:02.085 --> 00:04:06.380
the 3d sublevel and 4s are
very, very, very close,

00:04:06.380 --> 00:04:08.549
but it does turn out that most of the time

00:04:08.549 --> 00:04:09.956
what's going to react are the ones

00:04:09.956 --> 00:04:12.603
that are furthest out, the 4s1.

00:04:12.603 --> 00:04:14.876
So you could argue that
those are at the highest

00:04:14.876 --> 00:04:16.641
energy level, and so when you oxidize,

00:04:16.641 --> 00:04:18.963
you start pulling electrons off of zinc,

00:04:18.963 --> 00:04:21.168
you can pull off the 4s.

00:04:21.168 --> 00:04:24.084
You're more likely to
pull off the 4s electrons

00:04:24.084 --> 00:04:27.074
or you're going to pull
off the 4s electrons.