Carbon as a building block of life

WEBVTT
Kind: captions
Language: en

00:00:00.310 --> 00:00:04.960
You're probably already familiar with
some forms of carbon. For example this

00:00:04.960 --> 00:00:06.410
graph I write over here,

00:00:06.410 --> 00:00:09.540
this is one form carbon takes. Very
important when you're writing with a

00:00:09.540 --> 00:00:12.450
pencil, otherwise you would not see any
writing. If you didn't have the graphite

00:00:12.450 --> 00:00:13.889
scraping onto your,

00:00:13.889 --> 00:00:18.140
scraping onto your paper, which you and
your paper is also. It's not pure carbon,

00:00:18.140 --> 00:00:19.390
but it has a lot of carbon

00:00:19.390 --> 00:00:23.210
in it. This right over here is a raw
diamond,

00:00:23.210 --> 00:00:27.279
another form the carbon can take under
intense time or after a long period of

00:00:27.279 --> 00:00:28.470
time under intense

00:00:28.470 --> 00:00:31.760
pressure. But what you may or may not
realize

00:00:31.760 --> 00:00:36.100
is that carbon is actually essential for
life. In fact life as we know it

00:00:36.100 --> 00:00:39.120
is carbon-based, so carbon-based,

00:00:39.120 --> 00:00:43.190
based life. When we look for signs of
life, at least life as we know on other

00:00:43.190 --> 00:00:46.180
planets,we are looking for signs of
carbon-based life. And there might be

00:00:46.180 --> 00:00:47.579
other forms, other

00:00:47.579 --> 00:00:51.210
other elements that form the backbone of
life. But carbon is the only one

00:00:51.210 --> 00:00:54.770
that we have been able to observe. Now
why

00:00:54.770 --> 00:00:58.699
is carbon so valuable for life? Why does
it form the backbone

00:00:58.699 --> 00:01:03.239
of the molecules that make life
possible ? What all comes down to where it

00:01:03.239 --> 00:01:05.330
sits in the periodic table? And how many

00:01:05.330 --> 00:01:08.490
and its atomic number and how it tends
to bond with things?

00:01:08.490 --> 00:01:13.549
So this is why Chemistry is important.
So carbon we see over here has an

00:01:13.549 --> 00:01:14.860
atomic number six,

00:01:14.860 --> 00:01:17.890
which by definition means it has 6
protons.

00:01:17.890 --> 00:01:21.439
So far we draw its nucleus it would
have 1,2 ,

00:01:21.439 --> 00:01:24.799
3, 4, 5, 6 protons.

00:01:24.799 --> 00:01:28.280
And the most common isotope of carbon on earth

00:01:28.280 --> 00:01:32.590
is carbon 12, which also has six neutrons. So let
me draw that in this nucleus 1,

00:01:32.590 --> 00:01:35.960
2, 3, 4, 5, 6

00:01:35.960 --> 00:01:39.799
neutrons. And then neutral carbon is going to have six electrons.

00:01:39.799 --> 00:01:44.030
And so two of them are going to be in
their inner most in the first

00:01:44.030 --> 00:01:47.090
shell .So that's two of them right over
there.

00:01:47.090 --> 00:01:51.590
These are the inner
shell.  I guess you could say or the

00:01:51.590 --> 00:01:56.490
so that's the first two electrons ,and
then you have four remaining in its

00:01:56.490 --> 00:01:57.420
outermost shell.

00:01:57.420 --> 00:02:01.090
And these four considered valence
electrons, these are the electrons that

00:02:01.090 --> 00:02:02.080
actually do

00:02:02.080 --> 00:02:06.060
the reacting. And if any of this seems
unfamiliar to you,I encourage you to watch

00:02:06.060 --> 00:02:07.820
the videos on Khan Academy on things
like

00:02:07.820 --> 00:02:11.320
valence electrons, but this is a little
bit overview right over here.

00:02:11.320 --> 00:02:15.460
Carbon has four valence electrons.
Valence electrons are the ones

00:02:15.460 --> 00:02:18.660
that do or that tend to do the
reacting.

00:02:18.660 --> 00:02:22.580
And so I could if I wanted to simplify
this drawng over here,I could say ,"Okay

00:02:22.580 --> 00:02:26.440
carbon."And if I register as valence
electrons which is a typical thing to do.

00:02:26.440 --> 00:02:27.890
I could say carbon has 1,

00:02:27.890 --> 00:02:31.110
2, 3 ,4

00:02:31.110 --> 00:02:34.820
valence electrons. Now you might remember the octet rule that

00:02:34.820 --> 00:02:39.600
that atoms tend to be more stable when
they at least pretend, like they

00:02:39.600 --> 00:02:42.970
with that they're sharing or that they
have eight electrons in there outermost

00:02:42.970 --> 00:02:43.890
shell.

00:02:43.890 --> 00:02:47.550
So carbon can do that by forming 4
covalent bonds.

00:02:47.550 --> 00:02:51.680
For example it could do that with
hydrogen.This hydrogen over here has one

00:02:51.680 --> 00:02:55.270
valence electron. It actually has one
electron. Now the hydrogen feels good. It

00:02:55.270 --> 00:02:57.940
feels like its sharing two-electrons
filling its

00:02:57.940 --> 00:03:01.060
its first shell .Hydrogen is just trying to fill out the first

00:03:01.060 --> 00:03:04.950
shell, feel a little bit more like helium
and now carbon says," Oh,now I get to share

00:03:04.950 --> 00:03:07.920
share this electron." And then carbon can do it again with another hydrogen.

00:03:07.920 --> 00:03:12.239
It can do it again with another
hydrogen. And it can do it again

00:03:12.239 --> 00:03:17.720
with another hydrogen. So now carbon can feel like," Hey I'm sharing eight
electrons

00:03:17.720 --> 00:03:21.100
and the each of the hydrogens feel like, "Oh look you know I I'm sharing two

00:03:21.100 --> 00:03:24.530
electrons." Everyone seems to be happy
everyone seems to be stable.

00:03:24.530 --> 00:03:29.280
And this molecule right over here, this
is methane ,this is methane.

00:03:29.280 --> 00:03:34.010
And by definition because it involves
carbon it is considered an organic

00:03:34.010 --> 00:03:34.780
molecule.

00:03:34.780 --> 00:03:39.150
It is considered an organic molecule. In
fact, the whole

00:03:39.150 --> 00:03:42.530
the whole field of Organic Chemistry is
all about studying

00:03:42.530 --> 00:03:45.739
organic molecules which are molecules
that have carbon.

00:03:45.739 --> 00:03:50.160
Now because this only has carbon and
hydrogen in it,it  is also considered to be

00:03:50.160 --> 00:03:51.580
a Hydrocarbon.

00:03:51.580 --> 00:03:55.150
Hydrocarbon Hydrocarbon.

00:03:55.150 --> 00:03:59.900
And you might be familiar with things
like  gasoline being considered a

00:03:59.900 --> 00:04:02.060
Hydrocarbon. And it is indeed

00:04:02.060 --> 00:04:05.820
a Hydrocarbon. In fact gasoline gasoline actually even

00:04:05.820 --> 00:04:07.300
even methane could be

00:04:07.300 --> 00:04:12.230
used as fuel right over here. But in
typically you can see these long chains of

00:04:12.230 --> 00:04:13.040
hydrocarbons.

00:04:13.040 --> 00:04:17.250
For example, you could have 8 carbons
form octane. You might be familiar things

00:04:17.250 --> 00:04:19.010
like high octane fuel.

00:04:19.010 --> 00:04:22.620
So let's see carbon 2, 3,

00:04:22.620 --> 00:04:26.050
4, 5, 6, 7,

00:04:26.050 --> 00:04:29.130
8. This is a hydrocarbon. Its Octane because

00:04:29.130 --> 00:04:34.180
it has 8 carbons Oct, Octane. In  all the
other bonds remember carbon forms 4

00:04:34.180 --> 00:04:36.040
bonds. It typically forms 4 bonds.

00:04:36.160 --> 00:04:41.680
So now that carbon has 4 bonds. Now this
carbon has 4 bonds. Now this carbon

00:04:41.680 --> 00:04:45.620
2 of them to hydrogen ,2 of them to carbon.2 to hydrogen,

00:04:45.620 --> 00:04:48.860
2 to carbon. Hopefully this starts to give you an
appreciation why

00:04:48.860 --> 00:04:52.860
carbon is so useful as a building block
because it can form so many bonds with

00:04:52.860 --> 00:04:54.430
so many different structures.

00:04:54.430 --> 00:04:58.460
And these hydrocarbons they can be
chains or they can even form,

00:04:58.460 --> 00:05:02.280
they can even form rings they can form
cycles.And in things like

00:05:02.280 --> 00:05:06.780
graphite and in diamond carbons can form
these lattice structures, where you know

00:05:06.780 --> 00:05:07.750
know carbon is for

00:05:07.750 --> 00:05:11.090
is bonding. Carbon is forming is bonding
to

00:05:11.090 --> 00:05:14.260
more than two carbons in these three
dimensional shapes.

00:05:14.260 --> 00:05:17.380
In these three, in these three
dimensional

00:05:17.380 --> 00:05:20.680
shapes. And the shape because it's
forming three bonds

00:05:20.680 --> 00:05:23.730
that that carbon typically forms bonds in
these are called

00:05:23.730 --> 00:05:28.520
tetrahedral shapes or tetrahedral
bonding. And when someone says tetrahedron

00:05:28.520 --> 00:05:31.580
if someone says tetrahedron they're
talking about

00:05:31.580 --> 00:05:35.510
they're talking about a..Wait let me use
a different color.

00:05:35.510 --> 00:05:38.510
So a tetrahedron is

00:05:38.510 --> 00:05:43.040
a three-dimension, a three-dimensional
shape that has four sides each of which

00:05:43.040 --> 00:05:44.060
are triangles.

00:05:44.060 --> 00:05:48.440
Each of which are triangles. So it
would look

00:05:48.440 --> 00:05:52.040
like this. You could do it as a pyramid with a triangular base.

00:05:52.040 --> 00:05:56.020
A pyramid with a triangular base. And
when carbon forms bonds as in the case

00:05:56.020 --> 00:05:57.540
have this methane right over here.

00:05:57.540 --> 00:06:01.560
I'd rather the carbon in the middle as this,

00:06:01.560 --> 00:06:05.240
yellow circle ,then each of the hydrogens over here

00:06:05.240 --> 00:06:08.450
are going to be at the corners

00:06:08.450 --> 00:06:11.760
or at you say the vertices of
the tetrahedron.

00:06:11.760 --> 00:06:15.490
And so this is the tetrahedral shape
that carbon

00:06:15.490 --> 00:06:18.930
is actually forming. Of course you have
these co valent bonds right over here.

00:06:18.930 --> 00:06:23.729
Let me do this in a different color. You
have these covalent bonds over here

00:06:23.729 --> 00:06:27.990
and we could draw it like this. We could
draw these covalent bonds

00:06:27.990 --> 00:06:31.400
like this. That's 1 of them, maybe that's this one over here.

00:06:31.400 --> 00:06:36.550
This one over here is right over here.These electrons are all just buzzing around.

00:06:36.550 --> 00:06:39.630
And then the one we have over here and then

00:06:39.630 --> 00:06:43.010
you have one over here. So you might see methane

00:06:43.010 --> 00:06:46.690
sometimes just drawn like this. You might just see it drawn,

00:06:46.690 --> 00:06:50.080
you might just see it drawn like this.

00:06:50.080 --> 00:06:54.310
But it's really forming, it's really forming
 a tetrahedral

00:06:54.310 --> 00:06:58.870
a tetrahedral shape. Me finished drawing it, so

00:06:58.870 --> 00:07:04.580
hydrogen hydrogen hydrogen hydrogen where each of these lines represent a pair of
e

00:07:04.580 --> 00:07:05.400
electrons here.

00:07:05.400 --> 00:07:09.560
Eight electrons being shared in
aggregate, but the actual shape is closer

00:07:09.560 --> 00:07:10.070
to this.

00:07:10.070 --> 00:07:13.630
Now I'm claiming to you that it's the
backbone

00:07:13.630 --> 00:07:18.430
of life or life as we know it. And its
even the back bone of life is

00:07:18.430 --> 00:07:20.280
as you are.

00:07:20.280 --> 00:07:23.690
Life in the form of you.  We've
already talked about you being a

00:07:23.690 --> 00:07:24.390
majority

00:07:24.390 --> 00:07:28.180
water and that's why if you look at the
average human being is the average human

00:07:28.180 --> 00:07:29.280
being is going to be

00:07:29.280 --> 00:07:32.599
roughly depends on how much how hot well hydrated you are in

00:07:32.599 --> 00:07:36.260
your stage of development. The average human
being is going to be sixty-five percent

00:07:36.260 --> 00:07:40.450
oxygen by mass. So you are two-thirds

00:07:40.450 --> 00:07:43.800
oxygen that's because of all of the
water. Water is H2O.

00:07:43.800 --> 00:07:47.310
And oxygen forms the bulk of the mass of the water molecule.

00:07:47.310 --> 00:07:51.610
But in second place comes carbon. In
second place comes carbon.

00:07:51.610 --> 00:07:55.849
Carbon is approximately 18 % of your body's mass.

00:07:55.849 --> 00:07:59.890
And this is because everything, but the
non fluid ,the non liquid

00:07:59.890 --> 00:08:00.800
part of your body.

00:08:00.800 --> 00:08:02.800
In there's a lot of carbon going on there.

00:08:02.800 --> 00:08:05.849
This right over is a DNA molecule and so

00:08:05.849 --> 00:08:09.039
these little grey areas, this is
all carbon.

00:08:09.039 --> 00:08:12.300
This right over here, this right over
here

00:08:12.300 --> 00:08:16.909
is Hexokinase. I'm not going to go
into the details about what it does.

00:08:16.909 --> 00:08:20.460
But Hexokinas is a protein.

00:08:20.460 --> 00:08:25.330
Hexokinas and the teal colored that you see there,

00:08:25.330 --> 00:08:30.190
that is all carbon. That's all carbon.
This right over here is glucose.

00:08:30.190 --> 00:08:34.500
It is very sweet.It's an important way to regulate your body's energy.

00:08:34.500 --> 00:08:39.579
And the teal color that is carbon. This
is ATP, often considered to be the

00:08:39.579 --> 00:08:43.690
the molecular currency of the energy in
your body. And all the teal there this is

00:08:43.690 --> 00:08:44.769
carbon. This is why

00:08:44.769 --> 00:08:48.029
a lot, especially the non water part
of your body

00:08:48.029 --> 00:08:52.540
is carbon. So hopefully this gives you a
better appreciation for

00:08:52.540 --> 00:08:55.690
carbon. It's not just useful for
pencils and diamonds, but even if you're

00:08:55.690 --> 00:08:56.910
just looking at your hand

00:08:56.910 --> 00:08:58.829
You're looking at a lot of carbon.


Definition of pH

WEBVTT
Kind: captions
Language: en

00:00:00.150 --> 00:00:02.790
- [Voiceover] In the video on
the auto-ionization of water

00:00:02.790 --> 00:00:05.790
we saw that you could have
two neutral water molecules,

00:00:05.790 --> 00:00:09.650
but one of them could swipe
a hydrogen ion from the other

00:00:09.650 --> 00:00:12.490
and then you could be
left with a hydronium ion,

00:00:12.490 --> 00:00:15.150
and the one that had the
hydrogen ion swiped from it,

00:00:15.150 --> 00:00:17.550
remember a hydrogen ion
is really just a proton.

00:00:17.550 --> 00:00:19.420
This one actually gains an electron,

00:00:19.420 --> 00:00:21.420
it gains an electron from that hydrogen.

00:00:21.420 --> 00:00:25.250
It takes all the electrons
from this covalent bond,

00:00:25.250 --> 00:00:28.120
right over here, and it
forms another lone pair

00:00:28.120 --> 00:00:29.390
and it gets a negative charge,

00:00:29.390 --> 00:00:31.790
and that becomes a hydroxide ion.

00:00:31.790 --> 00:00:34.520
Or we could also describe that
auto-ionization like this,

00:00:34.520 --> 00:00:36.110
that if I have one water molecule,

00:00:36.110 --> 00:00:40.820
well the oxygen grabs
both of the electrons

00:00:40.820 --> 00:00:42.120
from this lone pair,

00:00:42.120 --> 00:00:44.490
swipes hydrogen of the
one electron it had,

00:00:44.490 --> 00:00:47.420
and all it's left with is its protons.

00:00:47.420 --> 00:00:50.990
Well, hydrogen ion, it's really
just talking about a proton

00:00:50.990 --> 00:00:52.950
because the most common
isotope of hydrogen

00:00:52.950 --> 00:00:55.420
only has a proton in it's nucleus,

00:00:55.420 --> 00:00:56.690
it does not have a neutron.

00:00:56.690 --> 00:00:57.890
So you take away its electron,

00:00:57.890 --> 00:01:00.050
you just have that proton left.

00:01:00.050 --> 00:01:01.620
And the whole point of doing this to show,

00:01:01.620 --> 00:01:04.150
well look, its not going
to be a typical thing,

00:01:04.150 --> 00:01:06.390
most of the water molecules
aren't going to be doing this,

00:01:06.390 --> 00:01:08.390
but this is going to happen

00:01:08.390 --> 00:01:11.450
if you have a large enough
quantity of water molecules.

00:01:11.450 --> 00:01:13.920
And we've even seen to
what degree that happens,

00:01:13.920 --> 00:01:16.220
how typical that is by
looking at the concentration.

00:01:16.220 --> 00:01:18.550
If we looked at the concentration,

00:01:18.550 --> 00:01:21.950
so if we're talking about pure water,

00:01:21.950 --> 00:01:24.420
we've seen that the concentration,

00:01:24.420 --> 00:01:25.890
and we can think about it in two ways.

00:01:25.890 --> 00:01:27.810
If we think about this top way

00:01:27.810 --> 00:01:29.590
of expressing the auto-ionization,

00:01:29.590 --> 00:01:32.810
we can say the concentration
of hydronium ions,

00:01:32.810 --> 00:01:35.090
or if we think about this one over here,

00:01:35.090 --> 00:01:37.950
we could think about the
concentration of hydrogen ions.

00:01:37.950 --> 00:01:39.590
And the reason why these
two things are equivalent,

00:01:39.590 --> 00:01:41.050
is because these hydrogen ions

00:01:41.050 --> 00:01:42.690
are really just going
to associate themselves

00:01:42.690 --> 00:01:45.690
with the water molecule
and become hydronium.

00:01:45.690 --> 00:01:48.120
But in pure water, at 25 degrees Celsius,

00:01:48.120 --> 00:01:50.750
we've seen that these are
going to be approximately

00:01:50.750 --> 00:01:52.420
the concentration, whether you think of it

00:01:52.420 --> 00:01:55.790
as hydronium concentration or
hydrogen ion concentration,

00:01:55.790 --> 00:01:58.490
it's going to be
approximately one times ten

00:01:58.490 --> 00:02:01.350
to the negative seven molar.

00:02:01.350 --> 00:02:02.520
What does that mean?

00:02:02.520 --> 00:02:04.720
Well molar, this is just
the units for molarity,

00:02:04.720 --> 00:02:06.690
that's the same thing as one times ten

00:02:06.690 --> 00:02:11.690
to the negative seven
moles, moles per liter.

00:02:12.290 --> 00:02:14.420
If you have trouble
remembering what moles are,

00:02:14.420 --> 00:02:15.890
first of all I encourage
you to watch that video

00:02:15.890 --> 00:02:17.220
on Kahn Academy on moles.

00:02:17.220 --> 00:02:19.020
But, we just have to remind
ourselves it's a quanity.

00:02:19.020 --> 00:02:21.650
Just as a dozen means twelve of something,

00:02:21.650 --> 00:02:24.190
a mole of something means 6.022 times,

00:02:24.190 --> 00:02:28.190
and roughly 6.022 times 10
to the 23rd of that thing.

00:02:28.190 --> 00:02:30.820
So it's just a very,
very, very large quanity.

00:02:30.820 --> 00:02:33.120
So that's the concentration,
that you could say

00:02:33.120 --> 00:02:34.520
the hydrogen ion concentration

00:02:34.520 --> 00:02:36.550
in pure water at 25 degrees Celsius.

00:02:36.550 --> 00:02:38.320
But, we could ask ourselves
that same question

00:02:38.320 --> 00:02:41.250
for other types of solutions.

00:02:41.250 --> 00:02:43.420
For example, orange juice.

00:02:43.420 --> 00:02:45.890
So let's just say right over here,

00:02:45.890 --> 00:02:50.290
so in orange juice,

00:02:50.290 --> 00:02:52.888
the hydrogen ion concentration,

00:02:52.888 --> 00:02:54.158
and once again I could also say

00:02:54.158 --> 00:02:56.518
this is a hydronium concentration.

00:02:56.518 --> 00:02:57.958
Depending on your glass of orange juice,

00:02:57.958 --> 00:02:59.688
it wouldn't be atypical to find a glass

00:02:59.688 --> 00:03:02.318
that has a hydrogen ion concentration

00:03:02.318 --> 00:03:07.318
of say one times ten to
the negative 3.5 molar.

00:03:08.388 --> 00:03:11.658
So once again, this is
actually a lot more then this,

00:03:11.658 --> 00:03:13.218
actually let me make it a round number,

00:03:13.218 --> 00:03:14.758
you actually might be
able to find something

00:03:14.758 --> 00:03:18.858
at one times ten to the
negative four molar.

00:03:18.858 --> 00:03:20.258
I looked it up on the internet,

00:03:20.258 --> 00:03:22.918
there's actually a range
kind of in the mid threes

00:03:22.918 --> 00:03:27.318
to low fours of hydrogen ion
concentration for orange juice.

00:03:27.318 --> 00:03:28.688
So you could find something like this,

00:03:28.688 --> 00:03:30.958
and as you can tell, it's
good to always just think

00:03:30.958 --> 00:03:32.358
about the numbers, this is actually

00:03:32.358 --> 00:03:35.518
a much higher concentration
than this over here.

00:03:35.518 --> 00:03:38.558
The exponent over here is less negative,

00:03:38.558 --> 00:03:40.288
so this is a higher concentration,

00:03:40.288 --> 00:03:44.038
so this is a higher concentration.

00:03:45.418 --> 00:03:48.488
We could look at something
that has a lower concentration.

00:03:48.488 --> 00:03:50.218
Say something like bleach.

00:03:50.218 --> 00:03:54.988
So bleach, I'll write
that right over here,

00:03:54.988 --> 00:03:57.288
I actually looked it up
on the Clorox website.

00:03:57.288 --> 00:03:58.188
The Clorox bleach,

00:03:58.188 --> 00:04:00.118
they say that their
hydrogen ion concentration

00:04:00.118 --> 00:04:04.488
is approximately - so their
hydrogen ion concentration -

00:04:04.488 --> 00:04:08.888
is approximately equal to one times ten

00:04:08.888 --> 00:04:13.888
to the negative twelve molar.

00:04:14.388 --> 00:04:16.658
So this is a much lower concentration

00:04:16.658 --> 00:04:19.988
than you would have in
just water right over here,

00:04:19.988 --> 00:04:22.018
in pure water at 25 degrees Celsius.

00:04:22.018 --> 00:04:23.858
So this is a much lower concentration,

00:04:23.858 --> 00:04:26.588
this exponent over here is more negative.

00:04:26.588 --> 00:04:29.058
This is a lower concentration.

00:04:29.058 --> 00:04:30.718
Well this is all well and good,

00:04:30.718 --> 00:04:33.388
but it can get a little bulky
talking about concentrations

00:04:33.388 --> 00:04:35.958
in terms of the scientific notation,

00:04:35.958 --> 00:04:38.818
something times something to
the negative whatever molar.

00:04:38.818 --> 00:04:40.518
So to help simplify that,

00:04:40.518 --> 00:04:44.458
people have invented the idea of a pH.

00:04:44.458 --> 00:04:46.918
Let me introduce it in a color

00:04:46.918 --> 00:04:48.488
that I have not used yet before.

00:04:48.488 --> 00:04:51.558
You use lowercase p, uppercase h.

00:04:51.558 --> 00:04:55.358
I've looked into where
this notation comes from,

00:04:55.358 --> 00:04:57.958
the h most people agree is
referring to the hydrogen

00:04:57.958 --> 00:04:59.818
in some way, but the p some people think

00:04:59.818 --> 00:05:01.658
is referring to potential,
some people just think

00:05:01.658 --> 00:05:03.618
it's a random letter
that was associated in

00:05:03.618 --> 00:05:05.458
with one of these historical artifacts.

00:05:05.458 --> 00:05:09.158
But, this is defined
as the negative log of,

00:05:09.158 --> 00:05:12.188
and we could say negative
log, if we don't write a base,

00:05:12.188 --> 00:05:13.858
you assume it's base 10.

00:05:13.858 --> 00:05:18.088
But, the negative log of the
hydrogen ion concentration,

00:05:18.088 --> 00:05:20.458
or it's equivalently the negative log,

00:05:20.458 --> 00:05:25.458
because the hydrogen ions are
really hydronium ions, H3O.

00:05:26.588 --> 00:05:29.488
It's really the same
thing as this as well.

00:05:29.488 --> 00:05:32.988
So given this definition of pH,

00:05:32.988 --> 00:05:35.658
let's calculate the pH's for pure water

00:05:35.658 --> 00:05:36.958
at 25 degrees Celsius,

00:05:36.958 --> 00:05:40.018
the pH of this glass of orange juice,

00:05:40.018 --> 00:05:42.158
or the pH of this bleach.

00:05:42.158 --> 00:05:44.858
Well, the pH of this pure
water is going to be,

00:05:44.858 --> 00:05:49.858
so the pH here, so I have
some space right over here,

00:05:52.988 --> 00:05:54.748
it's going to be the negative log,

00:05:54.748 --> 00:05:57.388
and I'll write the base 10
there just cause that's assumed,

00:05:57.388 --> 00:05:59.258
of its hydrogen ion concentration,

00:05:59.258 --> 00:06:01.588
which is one times ten to
the negative seven molar.

00:06:01.588 --> 00:06:03.358
We want molarity right over here,

00:06:03.358 --> 00:06:04.858
you want molarity right over here.

00:06:04.858 --> 00:06:06.488
Well, one times ten to the negative seven

00:06:06.488 --> 00:06:09.658
is the same thing as
ten to the negative 7,

00:06:09.658 --> 00:06:12.988
and if you look at just the
part where the log here,

00:06:12.988 --> 00:06:15.288
before we think about the negative.

00:06:15.288 --> 00:06:17.288
This is just saying to what
power do we have to raise ten,

00:06:17.288 --> 00:06:19.418
to get ten to the negative seven power?

00:06:19.418 --> 00:06:21.258
Well, that's just going
to be negative seven.

00:06:21.258 --> 00:06:23.218
If what I just did is confusing,

00:06:23.218 --> 00:06:25.858
I encourage you to review
logarithms on Khan Academy.

00:06:25.858 --> 00:06:28.788
So we're going to have the
negative of negative seven,

00:06:28.788 --> 00:06:33.788
which is going to be
equal to positive seven.

00:06:34.088 --> 00:06:38.218
So the pH of pure water
at 25 degrees Celsius,

00:06:38.218 --> 00:06:39.258
and temperature would matter

00:06:39.258 --> 00:06:41.458
because it might affect auto-ionization.

00:06:41.458 --> 00:06:44.854
The pH at 25 degrees celsius is seven.

00:06:44.854 --> 00:06:46.518
What about this orange juice?

00:06:46.518 --> 00:06:51.518
Well the pH over here is going
to be the negative log of -

00:06:54.258 --> 00:06:56.288
Instead of writing one times
ten to the negative four,

00:06:56.288 --> 00:06:58.488
I can just write ten to the negative four,

00:06:58.488 --> 00:07:00.418
and of course that's a base 10.

00:07:00.418 --> 00:07:02.358
Well, what do I have to raise ten to,

00:07:02.358 --> 00:07:03.558
to get ten to the negative four,

00:07:03.558 --> 00:07:05.288
well I'll have to raise that
to the negative four power.

00:07:05.288 --> 00:07:08.358
The negative of negative
four is positive four.

00:07:08.358 --> 00:07:12.418
By that same argument, or by
applying the same definition,

00:07:12.418 --> 00:07:16.458
the pH of this bleach is going to be equal

00:07:16.458 --> 00:07:20.758
to the negative log of ten
to the negative twelve.

00:07:20.758 --> 00:07:22.788
I'm just ignoring this
one times right over here,

00:07:22.788 --> 00:07:24.388
I could write one times
ten to the negative twelve,

00:07:24.388 --> 00:07:26.018
but that's not going to change its value.

00:07:26.018 --> 00:07:28.618
That of course is going to
be equal to the negative

00:07:28.618 --> 00:07:33.318
of negative twelve,
which is positive twelve.

00:07:33.318 --> 00:07:36.058
So it might be fun to plot all of these.

00:07:36.058 --> 00:07:37.358
Let me do that.

00:07:37.358 --> 00:07:40.088
So let me plot these pH's.

00:07:40.088 --> 00:07:45.088
So we draw a line right over here,

00:07:45.458 --> 00:07:50.458
and let's say that this is
zero, one, two, three, four -

00:07:53.858 --> 00:07:56.178
which I'm not gonna be able
to all the way to twelve,

00:07:56.178 --> 00:07:58.618
so I'll have to make my
scale a little bit smaller.

00:07:58.618 --> 00:08:03.618
Zero, one, two, three, four,
five, six, seven, eight, nine,

00:08:07.258 --> 00:08:12.258
ten, eleven, twelve, and I
could keep going over here.

00:08:12.388 --> 00:08:16.758
So let me write this, one,
two, three, four, five, six,

00:08:16.758 --> 00:08:21.588
seven, eight, nine, ten, eleven, twelve.

00:08:21.588 --> 00:08:23.918
So these are our pH's over
here, I could plot em.

00:08:23.918 --> 00:08:26.718
That water at 25 degrees Celsius

00:08:26.718 --> 00:08:30.618
is gonna be right over
here, and that is my water.

00:08:30.618 --> 00:08:33.388
That's sometimes referred
to as a neutral pH.

00:08:33.388 --> 00:08:36.258
If I look at that orange
juice with a pH of four,

00:08:36.258 --> 00:08:38.558
that orange juice is
gonna be right over here,

00:08:38.558 --> 00:08:40.218
and I've seen ranges for orange juice,

00:08:40.218 --> 00:08:42.888
that's actually more in
this range right over here,

00:08:42.888 --> 00:08:44.958
so depending on your glass, or
whether it's gone bad or not,

00:08:44.958 --> 00:08:47.318
so that's going to be orange juice,

00:08:47.318 --> 00:08:48.688
could be found in that range.

00:08:48.688 --> 00:08:53.688
So I'll write orange juice, orange juice.

00:08:53.888 --> 00:08:55.218
And then this bleach,

00:08:55.218 --> 00:08:58.088
and it depends on the
concentration and all of that,

00:08:58.088 --> 00:09:01.288
but this bleach in particular
is right over here,

00:09:01.288 --> 00:09:03.458
this bleach is right over here.

00:09:03.458 --> 00:09:05.758
I could plot other things, your stomach,

00:09:05.758 --> 00:09:08.258
the juices in your stomach,
are highly, highly -

00:09:08.258 --> 00:09:11.158
well I'll talk about the
acidic a little bit more -

00:09:11.158 --> 00:09:15.218
but your stomach juices are going to be -

00:09:15.218 --> 00:09:18.558
let me do this in a new color -

00:09:18.558 --> 00:09:23.058
are going to be in this
range right over here.

00:09:23.058 --> 00:09:28.058
So stomach acid, and often
instead of stomach juices,

00:09:28.418 --> 00:09:30.088
stomach acid.

00:09:30.088 --> 00:09:32.058
If you had something like seawater,

00:09:32.058 --> 00:09:37.058
it's going to be in this range,
right over here, seawater.

00:09:40.158 --> 00:09:42.658
Now let's think about
what this is telling us,

00:09:42.658 --> 00:09:44.818
and remember this is a logarithmic scale,

00:09:44.818 --> 00:09:49.818
as we go to the right, our
concentration is going down,

00:09:54.158 --> 00:09:55.118
it's important to recognize,

00:09:55.118 --> 00:09:57.688
and that's all because of
this negative right over here,

00:09:57.688 --> 00:09:58.818
in our definition.

00:09:58.818 --> 00:10:01.818
But we saw that bleach has
a much lower concentration

00:10:01.818 --> 00:10:03.518
than the water has.

00:10:03.518 --> 00:10:08.518
So this is lower hydrogen
ion concentration.

00:10:08.818 --> 00:10:10.718
As we go to the left we have

00:10:10.718 --> 00:10:13.618
a higher hydrogen ion concentration.

00:10:13.618 --> 00:10:16.618
Higher hydrogen ion concentration.

00:10:16.618 --> 00:10:19.288
In general, if something
has a pH below seven,

00:10:19.288 --> 00:10:23.018
we tend to refer to it as acidic.

00:10:23.018 --> 00:10:25.918
We say it is acidic.

00:10:25.918 --> 00:10:29.658
So typically when you add
acids to neutral water,

00:10:29.658 --> 00:10:31.888
your pH is going to go down,

00:10:31.888 --> 00:10:34.258
it's going to get more and more acidic.

00:10:34.258 --> 00:10:37.058
As you go to the right, if
you have a pH above seven,

00:10:37.058 --> 00:10:40.658
sometimes you'll hear people say basic

00:10:40.658 --> 00:10:43.818
and sometimes you also might
hear people say alkaline.

00:10:43.818 --> 00:10:47.088
It is becoming more alkaline,

00:10:47.088 --> 00:10:50.018
it's hydrogen concentration
is getting lower,

00:10:50.018 --> 00:10:53.918
and lower, and lower as
we move to the right.

00:10:53.918 --> 00:10:56.378
I really want you to appreciate
the logarithmic nature of it

00:10:56.378 --> 00:10:58.118
because if I handed you some seawater

00:10:58.118 --> 00:11:01.518
with a pH of eight, you
might say okay no big deal

00:11:01.518 --> 00:11:04.388
pH of eight relative to a pH of seven,

00:11:04.388 --> 00:11:06.358
but this is a logarithmic scale,

00:11:06.358 --> 00:11:07.688
if we're moving to the right,

00:11:07.688 --> 00:11:12.688
we have a ten times lower
concentration of hydrogen ions.

00:11:13.258 --> 00:11:16.818
If we were to move three
spaces to the right on this,

00:11:16.818 --> 00:11:20.358
where it's one-tenth,
one-tenth, one-tenth,

00:11:20.358 --> 00:11:24.358
we have one-thousandth the
concentration of hydrogen ions.

00:11:24.358 --> 00:11:26.018
It's pretty interesting to think about

00:11:26.018 --> 00:11:31.018
how much lower the hydrogen
concentration is in say bleach

00:11:31.288 --> 00:11:33.118
than in water, and how much lower that is

00:11:33.118 --> 00:11:37.117
than say stomach acid or orange juice.


Introduction to buffers

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:02.656
- [Voiceover] In order for our
bodies to function properly,

00:00:02.717 --> 00:00:06.631
the pH of our blood has to be
within a fairly narrow range.

00:00:06.631 --> 00:00:10.318
Our pH, so the pH of blood

00:00:10.318 --> 00:00:11.898
needs to be between

00:00:11.898 --> 00:00:15.544
seven point three five
and seven point four five.

00:00:15.544 --> 00:00:19.614
If the pH falls below
seven point three five,

00:00:19.614 --> 00:00:21.274
you're going to be diagnosed,

00:00:21.274 --> 00:00:24.509
and you know this line is, there
is kind of a gray area here

00:00:24.509 --> 00:00:26.302
but this is what's defined
by the medical community

00:00:26.302 --> 00:00:29.341
if your pH falls below
seven point three five,

00:00:29.341 --> 00:00:32.721
you're actually diagnosed with acidosis.

00:00:32.721 --> 00:00:34.749
Your blood is becoming too acidic.

00:00:34.749 --> 00:00:36.120
You have too high of a

00:00:36.120 --> 00:00:38.396
hydrogen ion concentration in your blood,

00:00:38.396 --> 00:00:40.673
or a hydronium
concentration in your blood.

00:00:40.673 --> 00:00:43.876
If your pH, if the pH
in your blood gets above

00:00:43.876 --> 00:00:48.266
seven point four five, you're
diagnosed with alkalosis.

00:00:48.266 --> 00:00:51.470
Alkalosis.
Your blood is too alkaline.

00:00:51.470 --> 00:00:54.992
It's becoming too basic.
The hydrogen concentration,

00:00:54.992 --> 00:00:57.003
hydrogen ion concentration in your blood

00:00:57.003 --> 00:00:59.162
is getting too low.

00:00:59.718 --> 00:01:01.487
And so you might say, "Wow,
you know this feels like

00:01:01.487 --> 00:01:04.391
a fairly narrow range. How
does blood, how does our body

00:01:04.391 --> 00:01:07.633
put up with acidic
things, acidic molecules

00:01:07.633 --> 00:01:11.578
entering our blood, or basic
molecules entering our blood.

00:01:11.578 --> 00:01:14.078
How can it handle that without our pH,

00:01:14.078 --> 00:01:18.278
while keeping our pH in
this range right over here?"

00:01:18.558 --> 00:01:22.084
And the answer lies in
something that's also useful

00:01:22.084 --> 00:01:25.811
for the transportation of
carbon dioxide in our blood.

00:01:25.811 --> 00:01:29.573
And this right over here,
these equilibrium reactions,

00:01:29.573 --> 00:01:32.248
we see that carbon dioxide,
when you put it in the blood,

00:01:32.248 --> 00:01:34.139
which is primarily water,

00:01:34.139 --> 00:01:37.988
so carbon dioxide in aqueous
solution, it will react.

00:01:37.988 --> 00:01:41.074
And we have some enzymes
that help this along,

00:01:41.074 --> 00:01:44.091
but it will react to form carbonic acid.

00:01:44.091 --> 00:01:48.070
Let me write this down. It will
react to form carbonic acid,

00:01:48.070 --> 00:01:50.970
which is a weak acid,
this is carbonic adic.

00:01:50.970 --> 00:01:54.013
And then that can dissociate
to form bicarbonate.

00:01:55.203 --> 00:01:56.198
Let me write that over here.

00:01:56.198 --> 00:01:59.369
Bicarbonate.
Bicarbonate.

00:01:59.744 --> 00:02:02.815
And a hydrogen ion, or when
we know that that would

00:02:02.815 --> 00:02:06.838
just attach to a water molecule
and become a hydronium ion.

00:02:06.838 --> 00:02:08.723
And so, why is this useful?

00:02:08.723 --> 00:02:10.134
Well, I said, it's actually part of

00:02:10.134 --> 00:02:13.765
the carbon dioxide transportation
in the blood because,

00:02:13.765 --> 00:02:15.331
based on the sources I've looked at,

00:02:15.331 --> 00:02:18.050
about five to 10 percent
of your carbon dioxide

00:02:18.050 --> 00:02:19.701
can just dissolve in the blood

00:02:19.701 --> 00:02:22.793
and then also another,
roughly, five or 10 percent

00:02:22.793 --> 00:02:26.733
can actually be bound to hemoglobin

00:02:26.733 --> 00:02:28.184
and be transported that way.

00:02:28.184 --> 00:02:30.919
But the bulk of it actually
needs to go through,

00:02:30.919 --> 00:02:34.793
needs to actually be
transformed, needs to react

00:02:34.793 --> 00:02:36.787
to become carbonic acid and bicarbonate

00:02:36.787 --> 00:02:38.597
in order to be transported.

00:02:38.597 --> 00:02:41.346
In fact, in your blood,
most of the carbon dioxide

00:02:41.346 --> 00:02:44.205
in your blood is actually in
this form right over here.

00:02:44.205 --> 00:02:46.179
And in particular, bicarbonate.

00:02:46.179 --> 00:02:47.829
In the sources that I look at,

00:02:47.829 --> 00:02:50.078
80 to 90 percent of the
carbon dioxide in your blood

00:02:50.078 --> 00:02:51.879
is being transported in these forms,

00:02:51.879 --> 00:02:55.556
and primarily as bicarbonate.

00:02:55.556 --> 00:02:57.838
So this isn't the topic of this video,

00:02:57.838 --> 00:03:01.681
what's a useful way to transfer,
to transport carbon dioxide

00:03:01.681 --> 00:03:05.149
in your blood, but this is how we do it.

00:03:05.149 --> 00:03:07.034
But the topic of this video is why this is

00:03:07.034 --> 00:03:11.510
also useful for maintaining
our blood pH in this range.

00:03:11.510 --> 00:03:13.686
Because these equilibrium
reactions between

00:03:13.686 --> 00:03:17.168
carbon dioxide, carbonic
acid, and bicarbonate

00:03:17.168 --> 00:03:19.486
this is a buffer system.

00:03:20.179 --> 00:03:24.673
This is a buffer, this is a buffer system.

00:03:24.673 --> 00:03:27.370
And the word "buffer,"
in our everyday language,

00:03:27.370 --> 00:03:30.243
it refers to something
that kind of smooths

00:03:30.243 --> 00:03:31.632
the impact of something,

00:03:31.632 --> 00:03:33.914
or it reduces the shock of something.

00:03:33.914 --> 00:03:35.977
And that's exactly what's happening here.

00:03:35.977 --> 00:03:37.376
Let's think about, remember,

00:03:37.376 --> 00:03:38.906
these are all equilibrium reactions,

00:03:38.906 --> 00:03:42.207
this is a weak acid, and you
can even look at the different

00:03:42.207 --> 00:03:44.981
constituents of these
molecules and account for them.

00:03:44.981 --> 00:03:46.302
You have one carbon here,

00:03:46.302 --> 00:03:47.288
one carbon here,

00:03:47.288 --> 00:03:48.335
one carbon there.

00:03:48.335 --> 00:03:50.368
You have one, two, three oxygens there.

00:03:50.368 --> 00:03:52.030
You have one, two, three oxygens there.

00:03:52.030 --> 00:03:53.554
One, two, three oxygens there.

00:03:53.554 --> 00:03:56.301
You have two hydrogens, two
hydrogens, two hydrogens.

00:03:56.301 --> 00:03:58.313
But let's just think about what if you

00:03:58.313 --> 00:04:00.749
started dumping hydrogen
ions in the blood.

00:04:00.749 --> 00:04:05.524
So, what if you were
to dump hydrogen ions,

00:04:08.164 --> 00:04:09.453
what's going to happen?

00:04:09.453 --> 00:04:11.245
Well, if you dump more hydrogen ions,

00:04:11.245 --> 00:04:14.396
if this right over here increases.

00:04:14.396 --> 00:04:16.539
Actually, let me put it this way,

00:04:16.539 --> 00:04:17.974
if you were to just dump hydrogen ions

00:04:17.974 --> 00:04:19.848
and if you didn't have this buffer system,

00:04:19.848 --> 00:04:22.285
then your pH would decrease.

00:04:22.285 --> 00:04:24.534
Your pH would go down,
and if you do it enough,

00:04:24.534 --> 00:04:27.264
your pH, you would end up with acidosis.

00:04:27.264 --> 00:04:29.584
But lucky for us, we
have this buffer system.

00:04:29.584 --> 00:04:34.017
And so if you increase your
hydrogen ion concentrations,

00:04:34.017 --> 00:04:36.786
Le Chatelier's principle tells us,

00:04:36.786 --> 00:04:38.770
"Hey, these equilibrium reactions

00:04:38.770 --> 00:04:41.040
are going to move to the left."

00:04:41.040 --> 00:04:44.901
So the more hydrogen ions you
have sitting in the blood,

00:04:44.901 --> 00:04:46.372
the more likely they're gonna bump

00:04:46.372 --> 00:04:48.487
into the bicarbonate in just the right way

00:04:48.487 --> 00:04:51.135
to form carbonic acid.

00:04:51.135 --> 00:04:54.017
And the more carbonic acid
that you have in the blood,

00:04:54.017 --> 00:04:56.043
well, it's the less likely
that you're going to have

00:04:56.043 --> 00:04:58.036
the carbon dioxide reacting with the water

00:04:58.036 --> 00:05:00.736
to form more carbonic acid.

00:05:00.736 --> 00:05:02.901
So, as you add more hydrogen ions,

00:05:02.901 --> 00:05:05.240
they're just going to be sopped up

00:05:05.240 --> 00:05:06.806
by the bicarbonate.

00:05:06.806 --> 00:05:09.198
So this equilibrium, this
set of equilibrium reactions

00:05:09.198 --> 00:05:11.333
is going to move to the left.

00:05:11.333 --> 00:05:14.425
So you're not going to
have as big effect on pH.

00:05:14.425 --> 00:05:18.830
And similarly, if you dumped some base,

00:05:18.830 --> 00:05:21.860
let's say, you dumped some base

00:05:21.860 --> 00:05:25.194
in your blood right over here,

00:05:25.194 --> 00:05:29.071
well, instead of it just
making your pH go up,

00:05:29.071 --> 00:05:31.014
and possibly give you alkalosis,

00:05:31.014 --> 00:05:33.961
well now, the base is going
to sop up the hydrogen ions,

00:05:33.961 --> 00:05:36.555
and typically that would
just make your pH go up,

00:05:36.555 --> 00:05:39.972
but if you have these things going down,

00:05:39.972 --> 00:05:42.538
well then, you have
fewer of these to react

00:05:42.538 --> 00:05:44.641
and have the equilibrium
reaction go to the left

00:05:44.641 --> 00:05:45.951
and so the reaction is going to move

00:05:45.951 --> 00:05:48.066
more and more to the right.

00:05:48.066 --> 00:05:49.599
And so this reaction,
you're just gonna have more

00:05:49.599 --> 00:05:51.933
carbon dioxide being
converted to carbonic acid

00:05:51.933 --> 00:05:53.567
being converted to bicarbonate.

00:05:53.567 --> 00:05:56.235
This whole thing is going
to move to the right.

00:05:56.235 --> 00:05:58.029
And so it's going to be
able, to some degree,

00:05:58.029 --> 00:06:00.854
replace the lost hydrogen ions.

00:06:00.854 --> 00:06:03.172
So this right over here's a buffer system.

00:06:03.172 --> 00:06:06.558
It helps dampen the
impact, as if you have more

00:06:06.558 --> 00:06:08.532
hydrogen ions enter the system,

00:06:08.532 --> 00:06:09.811
or as if you have something

00:06:09.811 --> 00:06:12.149
sopping up all of the hydrogen ions.

00:06:12.149 --> 00:06:14.049
And it's super important for us,

00:06:14.049 --> 00:06:15.510
well, just being able to live.

00:06:15.510 --> 00:06:18.093
And frankly, all mammalian systems.


Arrhenius definition of acids and bases

WEBVTT
Kind: captions
Language: en

00:00:00.481 --> 00:00:01.828
- [Voiceover] The first,
I guess you could say,

00:00:01.828 --> 00:00:04.487
modern conception of an acid and base

00:00:04.487 --> 00:00:06.634
comes from this gentleman right over here,

00:00:06.634 --> 00:00:08.665
Svante Arrhenius, and he was actually

00:00:08.665 --> 00:00:13.665
the third recipient of the Nobel
Prize in Chemistry in 1903.

00:00:13.665 --> 00:00:17.228
And his definition of
acids, under his definition

00:00:17.228 --> 00:00:20.607
of acids and bases, an acid
is something that increases

00:00:20.607 --> 00:00:23.186
the concentration, increases

00:00:25.815 --> 00:00:29.106
the concentration, concentration

00:00:31.075 --> 00:00:34.770
of Hydrogen protons,

00:00:34.770 --> 00:00:36.482
and we can say protons

00:00:37.648 --> 00:00:40.445
when put in an aqueous solution,

00:00:41.428 --> 00:00:45.685
when in aqueous, aqueous solution,

00:00:45.685 --> 00:00:48.065
and that's just a water solution.

00:00:48.065 --> 00:00:51.083
And then you can imagine
what a base would be.

00:00:51.083 --> 00:00:52.369
You could think, oh
maybe a base is something

00:00:52.369 --> 00:00:54.074
that decreases the protons and that's

00:00:54.074 --> 00:00:54.991
one way to think about it.

00:00:54.991 --> 00:00:58.799
Or you could say, it decreases,

00:00:58.799 --> 00:01:00.769
or actually let me
write this, it increases

00:01:05.373 --> 00:01:07.730
the hydroxide concentration.

00:01:07.730 --> 00:01:11.277
It increases the hydroxide concentration.

00:01:15.833 --> 00:01:19.583
when put in aqueous solution.

00:01:19.583 --> 00:01:23.619
When in aqueous, aqueous solution.

00:01:23.619 --> 00:01:24.849
So let's make that concrete.

00:01:24.849 --> 00:01:27.159
Let's look at some examples.

00:01:27.159 --> 00:01:29.622
So a strong Arrhenius acid, and actually,

00:01:29.622 --> 00:01:32.279
this would be a strong acid
by other definitions as well,

00:01:32.279 --> 00:01:34.380
would be hydrochloric acid.

00:01:34.380 --> 00:01:35.983
Hydrochloric acid,

00:01:35.983 --> 00:01:38.166
you put it in a an aqueous solution.

00:01:38.166 --> 00:01:40.220
So that's the hydrogen.

00:01:40.220 --> 00:01:42.681
You have the chlorine.

00:01:42.681 --> 00:01:44.745
You put it in an aqueous solution.

00:01:45.757 --> 00:01:47.978
You put it in an aqueous solution,

00:01:47.978 --> 00:01:50.057
it will readily disassociate.

00:01:50.057 --> 00:01:51.775
This is a, this reaction occurs,

00:01:51.775 --> 00:01:55.024
strongly favors moving
from the left to right.

00:01:55.024 --> 00:01:58.565
You're going to have
the chlorine strip off

00:01:58.565 --> 00:02:03.186
the two electrons in the
covalent bond with the hydrogen,

00:02:03.186 --> 00:02:05.310
leaving the hydrogen with no electrons,

00:02:05.310 --> 00:02:06.356
so the hydrogen is just going

00:02:06.356 --> 00:02:09.454
to be left as a hydrogen proton.

00:02:09.454 --> 00:02:11.811
And then the chlorine,

00:02:11.811 --> 00:02:14.191
the chlorine has just
nabbed that electron.

00:02:14.191 --> 00:02:16.548
It had the electrons it had
before, and then it just nabbed

00:02:16.548 --> 00:02:19.450
an electron from the
hydrogen, and so it now has

00:02:19.450 --> 00:02:20.971
a negative charge, and these are

00:02:20.971 --> 00:02:23.153
both in aqueous solution still.

00:02:23.153 --> 00:02:27.356
It's still, they're still
both dissolved in the water.

00:02:27.356 --> 00:02:28.935
And so you see very clearly here,

00:02:28.935 --> 00:02:30.571
you put this in an aqueous solution,

00:02:30.571 --> 00:02:33.532
you're going to increase the amount of,

00:02:33.532 --> 00:02:36.075
you're going to increase
the amount of hydrogen ions,

00:02:36.075 --> 00:02:38.397
the amount of protons in the solution.

00:02:38.397 --> 00:02:39.844
And we've talked about this before,

00:02:39.844 --> 00:02:42.235
you'll often see a
reaction written like this,

00:02:42.235 --> 00:02:44.414
but the hydrogen protons,
they just don't sit there

00:02:44.414 --> 00:02:45.911
by themselves in the water.

00:02:45.911 --> 00:02:48.930
They are going to bond with the water

00:02:48.930 --> 00:02:51.856
molecules to actually form hydronium.

00:02:51.856 --> 00:02:54.908
So another way that you'll
often see this is like this.

00:02:54.908 --> 00:02:57.184
You have the hydrochloric acid,

00:02:57.184 --> 00:02:59.366
hydrochloric acid.

00:02:59.366 --> 00:03:01.351
It's in an aqueous solution,

00:03:01.351 --> 00:03:04.126
just a fancy way of saying
it's dissolved in the water,

00:03:04.126 --> 00:03:07.632
and then you have the H2O.

00:03:07.632 --> 00:03:09.188
You have the water molecules,

00:03:09.188 --> 00:03:13.995
H2O, and you'll sometimes see written,

00:03:13.995 --> 00:03:16.583
okay, it's in its liquid form,

00:03:16.583 --> 00:03:19.195
and it's going to yield.

00:03:19.195 --> 00:03:21.714
Instead of just saying that
you have a hydrogen ion

00:03:21.714 --> 00:03:24.165
right over here, you'll
say, "Okay, that thing,

00:03:24.165 --> 00:03:26.138
"the hydrogen is actually gonna get bonded

00:03:26.138 --> 00:03:27.822
"to a water molecule."

00:03:27.822 --> 00:03:29.083
And so what you're gonna be left with

00:03:29.083 --> 00:03:31.249
is actually H3O.

00:03:35.546 --> 00:03:37.707
Now this thing, this was a water molecule,

00:03:37.707 --> 00:03:39.587
and all it got was a hydrogen ion.

00:03:39.587 --> 00:03:41.049
All that is is a proton.

00:03:41.049 --> 00:03:42.988
It didn't come with any electrons,

00:03:42.988 --> 00:03:46.029
so now this is going to
have a positive charge.

00:03:46.029 --> 00:03:47.969
It's going to have a positive charge,

00:03:47.969 --> 00:03:50.232
and we could now say
that this is going to be

00:03:50.232 --> 00:03:53.587
in an aqueous solution, hydronium

00:03:53.587 --> 00:03:56.745
is going to be in an aqueous solution,

00:03:56.745 --> 00:03:59.508
and you're going to have plus,

00:03:59.508 --> 00:04:02.179
now you're going to still
have the chloride ion,

00:04:02.179 --> 00:04:04.662
or it's a negative ion,
so we call it an anion.

00:04:04.662 --> 00:04:07.681
Chloride, chloride anion,

00:04:07.681 --> 00:04:11.233
and this is still in an aqueous solution.

00:04:11.233 --> 00:04:13.102
It is dissolved in water,

00:04:13.102 --> 00:04:14.576
and remember all that happened here

00:04:14.576 --> 00:04:17.003
is that the chlorine here
took all of the electrons,

00:04:17.003 --> 00:04:18.536
leaving hydrogen with none.

00:04:18.536 --> 00:04:21.078
Then that hydrogen proton gets
nabbed by a water molecule

00:04:21.078 --> 00:04:22.843
and becomes hydronium.

00:04:22.843 --> 00:04:24.699
So even by this definition you might say

00:04:24.699 --> 00:04:27.219
it increases the concentration
of hydrogen protons.

00:04:27.219 --> 00:04:31.119
You could say it increase the
concentration of hydronium,

00:04:31.119 --> 00:04:33.696
of hydronium right over here.

00:04:33.696 --> 00:04:36.924
Hydronium ions.

00:04:36.924 --> 00:04:39.339
So that makes, by the
Arrhenius definition,

00:04:39.339 --> 00:04:42.707
that makes hydrochloric
acid a strong acid.

00:04:42.707 --> 00:04:44.589
That makes it a

00:04:48.809 --> 00:04:50.446
strong acid.

00:04:50.446 --> 00:04:53.743
Now what would be a strong base
by the Arrhenius definition

00:04:53.743 --> 00:04:55.682
of acids and bases?

00:04:55.682 --> 00:04:59.025
Well one would be sodium hydroxide.

00:04:59.025 --> 00:05:00.430
So let me write that down,

00:05:00.430 --> 00:05:02.531
so if I have sodium hydroxide,

00:05:02.531 --> 00:05:05.028
sodium Na, that's the sodium,

00:05:05.028 --> 00:05:07.292
and then I have the hydroxide.

00:05:07.292 --> 00:05:11.649
That's an oxygen bonded to a hydrogen.

00:05:11.649 --> 00:05:13.457
So that's sodium hydroxide, and actually

00:05:13.457 --> 00:05:15.930
if you wanted to see what
this molecule looked like

00:05:15.930 --> 00:05:19.930
you have a oxygen having a covalent bond

00:05:19.930 --> 00:05:21.195
to a hydrogen.

00:05:21.195 --> 00:05:23.250
Let me do these in different colors.

00:05:23.250 --> 00:05:26.132
Oxygen has a covalent bond

00:05:26.132 --> 00:05:27.584
to a hydrogen.

00:05:28.506 --> 00:05:30.911
to a hydrogen right over here.

00:05:30.911 --> 00:05:35.670
And it actually has three alone pairs.

00:05:35.670 --> 00:05:38.815
It actually has three alone
pairs right over here.

00:05:38.815 --> 00:05:40.998
It's actually nabbed the electron from,

00:05:40.998 --> 00:05:42.832
from somebody some place,

00:05:42.832 --> 00:05:45.654
and so it's going to
have a negative charge.

00:05:45.654 --> 00:05:47.197
It is going to have a negative charge.

00:05:47.197 --> 00:05:48.162
Actually I could write it both,

00:05:48.162 --> 00:05:48.938
let me just write it like that.

00:05:48.938 --> 00:05:50.622
It has a negative charge,

00:05:50.622 --> 00:05:54.082
and then you have a sodium ion

00:05:54.082 --> 00:05:56.496
that has lost its electron somehow.

00:05:56.496 --> 00:06:00.083
So you have a sodium ion that has lost

00:06:00.083 --> 00:06:03.148
an electron somehow, so
it has a positive charge,

00:06:03.148 --> 00:06:05.609
and for all we know, it
could have lost the electron

00:06:05.609 --> 00:06:09.742
to the oxygen right over
here, making the oxygen

00:06:09.742 --> 00:06:12.065
negative and making the sodium positive,

00:06:12.065 --> 00:06:14.211
and so this is now
positive, this is negative,

00:06:14.211 --> 00:06:15.884
they're going to be
attracted to each other,

00:06:15.884 --> 00:06:17.950
and they form an ionic bond,

00:06:17.950 --> 00:06:20.724
so sodium hydroxide,
they have an ionic bond

00:06:20.724 --> 00:06:23.011
because the sodium is actually positive,

00:06:23.011 --> 00:06:25.101
and the hydroxide part right over here.

00:06:25.101 --> 00:06:27.225
That is negative,

00:06:27.225 --> 00:06:29.466
and that's what draws them together,

00:06:29.466 --> 00:06:32.728
but anyway, you put this
in an aqueous solution.

00:06:32.728 --> 00:06:36.768
You throw some sodium hydroxide
into an aqueous solution,

00:06:36.768 --> 00:06:40.034
it will disassociate into,

00:06:40.034 --> 00:06:44.931
into sodium with its positive
charge, the sodium ions,

00:06:44.931 --> 00:06:47.137
and actually you know the sodium
ion is still part of this.

00:06:47.137 --> 00:06:50.595
That's what makes it attracted
to the hydroxide anion,

00:06:50.595 --> 00:06:52.607
but it's still going to be

00:06:52.607 --> 00:06:55.440
in an aqueous solution,

00:06:55.440 --> 00:06:57.866
and then you're going
to have the hydroxide.

00:06:57.866 --> 00:07:00.759
You're going to have the hydroxide anion,

00:07:01.766 --> 00:07:04.364
so essentially this
thing just disassociates.

00:07:04.364 --> 00:07:05.977
This has a negative charge,

00:07:05.977 --> 00:07:08.566
and it's still going to
be dissolved in the water,

00:07:08.566 --> 00:07:10.726
so aqueous solution.

00:07:10.726 --> 00:07:12.838
So you throw sodium hydroxide in water,

00:07:12.838 --> 00:07:15.045
it's going to increase the concentration.

00:07:15.045 --> 00:07:18.414
It's going to increase the
concentration of hydroxide

00:07:18.414 --> 00:07:19.108
in the water.

00:07:19.108 --> 00:07:21.232
It's going to increase the
hydroxide concentration,

00:07:21.232 --> 00:07:24.284
and so by the Arrhenius
definition of acids and bases,

00:07:24.284 --> 00:07:27.213
this would be a strong Arrhenius base.

00:07:28.209 --> 00:07:30.352
This would be a strong,

00:07:30.352 --> 00:07:35.135
a strong base by the Arrhenius definition.

00:07:35.135 --> 00:07:38.084
Now, and I encourage you to look at that

00:07:38.084 --> 00:07:39.988
relative to the other definitions,

00:07:39.988 --> 00:07:42.844
the Bronsted-Lowry
definition of acids and bases

00:07:42.844 --> 00:07:45.224
and the Lewis definition
of acids and bases,

00:07:45.224 --> 00:07:48.132
and see how you would think
about categorizing things.


Brønsted–Lowry acids and bases

WEBVTT
Kind: captions
Language: en

00:00:00.279 --> 00:00:02.412
- [Voiceover] You've
probably heard the term acid

00:00:02.412 --> 00:00:04.800
used in your everyday life.

00:00:04.800 --> 00:00:05.998
But what we want to do in this video

00:00:05.998 --> 00:00:08.091
is get a more formal
definition of an acid.

00:00:08.091 --> 00:00:09.452
And particular, we'll focus on the one

00:00:09.452 --> 00:00:11.240
that is most typically used.

00:00:11.240 --> 00:00:13.414
Although we'll see future
videos that there's

00:00:13.414 --> 00:00:16.543
other fairly common definitions
of acids used as well

00:00:16.543 --> 00:00:18.209
beyond the one that
we're going to see here.

00:00:18.209 --> 00:00:19.468
But the one that we're going to focus on

00:00:19.468 --> 00:00:22.883
is the Bronsted-Lowry definition.

00:00:22.883 --> 00:00:26.048
The Bronsted-Lowry definition
of acids and bases.

00:00:26.048 --> 00:00:27.531
And this is a picture of Bronsted.

00:00:27.531 --> 00:00:28.771
This is a picture of Lowry.

00:00:28.771 --> 00:00:31.554
And they came up with
this acid-base definition

00:00:31.554 --> 00:00:33.410
in the 1920s.

00:00:33.410 --> 00:00:35.786
So, we're going to do the Bronsted-Lowry,

00:00:35.786 --> 00:00:38.976
Bronsted-Lowry definition,

00:00:38.976 --> 00:00:41.150
definition of acids and bases.

00:00:41.150 --> 00:00:43.953
So, according to them, according to them,

00:00:43.953 --> 00:00:48.953
an acid, an acid is a proton,

00:00:49.389 --> 00:00:50.069
proton,

00:00:50.069 --> 00:00:51.633
or instead of writing proton
we could actually write

00:00:51.633 --> 00:00:54.620
hydrogen ion donor.

00:00:54.620 --> 00:00:57.640
So why is a proton and a
hydrogen ion the same thing?

00:00:57.660 --> 00:01:01.014
Well, in the most common
isotope of hydrogen,

00:01:01.014 --> 00:01:03.005
we would, in it's nucleus, we would find

00:01:03.005 --> 00:01:05.829
just a proton and no neutron.

00:01:05.829 --> 00:01:09.384
And if it's neutral, you
would have an electron

00:01:09.384 --> 00:01:12.452
buzzing around, jumping
around in its orbital.

00:01:12.452 --> 00:01:14.321
So, you would have it's
electron jumping around

00:01:14.321 --> 00:01:16.009
in its orbital.

00:01:16.009 --> 00:01:17.470
But if you were to ionize it,

00:01:17.470 --> 00:01:19.380
you're getting rid of its electron.

00:01:19.380 --> 00:01:21.615
So, if you're getting
rid of it's electron,

00:01:21.615 --> 00:01:23.159
so, if you're getting rid of this,

00:01:23.159 --> 00:01:25.739
all you're going to be
left with is a proton.

00:01:25.739 --> 00:01:28.381
So that's why a proton, an H plus,

00:01:28.381 --> 00:01:31.266
is usually referring to the exact same,

00:01:31.266 --> 00:01:33.968
is referring to the exact same thing.

00:01:33.968 --> 00:01:35.085
So, that's what an acid is.

00:01:35.085 --> 00:01:36.533
So what would a base be?

00:01:36.533 --> 00:01:38.783
Well, you could imagine by this definition

00:01:38.783 --> 00:01:42.805
A base, a base would be a proton,

00:01:42.805 --> 00:01:45.322
would be a proton, or you could say

00:01:45.322 --> 00:01:49.772
a hydrogen ion acceptor, acceptor.

00:01:49.772 --> 00:01:51.458
So let's make this a
little bit more tangible

00:01:51.458 --> 00:01:52.901
with some examples.

00:01:52.901 --> 00:01:54.851
So one of the stronger acids we know

00:01:54.851 --> 00:01:57.004
is hydrochloric acid.

00:01:57.004 --> 00:01:59.402
Let me, let me draw.

00:01:59.402 --> 00:02:04.219
So, it's a hydrogen having
a, having a covalent bond.

00:02:04.219 --> 00:02:08.179
Having a covalent bond with chlorine.

00:02:08.179 --> 00:02:12.354
With chlorine, with
chlorine right over there.

00:02:12.354 --> 00:02:13.417
And if we want to,

00:02:13.417 --> 00:02:15.217
let's draw actually chlorine's lone pairs.

00:02:15.217 --> 00:02:18.733
So outside of the electron
that is contributing

00:02:18.733 --> 00:02:20.623
to this pair in the covalent bond.

00:02:20.623 --> 00:02:25.174
It also has, it also has
three other lone pairs.

00:02:25.174 --> 00:02:28.090
It also has three other
lone pairs, just like that.

00:02:28.090 --> 00:02:30.731
So, if you were to take hydrochloric acid,

00:02:30.731 --> 00:02:33.942
place it in an aqueous solution,

00:02:33.942 --> 00:02:37.518
so it's in an aqueous
solution right over here.

00:02:37.518 --> 00:02:38.512
And actually an aqueous solution,

00:02:38.512 --> 00:02:40.341
you'll see this written like that.

00:02:40.341 --> 00:02:42.497
That just means it's
in a solution of water.

00:02:42.497 --> 00:02:44.811
So you could write like
this, you could write hey,

00:02:44.811 --> 00:02:47.596
hydrochloric acid in an aqueous solution

00:02:47.596 --> 00:02:50.256
if you want to make it a
little bit more explicit.

00:02:50.256 --> 00:02:51.454
You could say hey, look,
this is going to be

00:02:51.454 --> 00:02:55.497
around some water molecules
in its liquid form.

00:02:55.497 --> 00:02:58.768
Aqueous solution just means
it's dissolved in liquid water.

00:02:58.768 --> 00:03:02.569
So, some water molecules
in their liquid form.

00:03:02.569 --> 00:03:04.985
So, this is a water molecule.

00:03:04.985 --> 00:03:07.404
Whoops, water molecule.

00:03:07.404 --> 00:03:10.999
Right over here.

00:03:10.999 --> 00:03:14.485
So, an oxygen bonded to two hydrogens.

00:03:14.485 --> 00:03:16.805
And sometimes you'll see
it written like this,

00:03:16.805 --> 00:03:20.297
that it's in its liquid,
it's in its liquid form.

00:03:20.297 --> 00:03:23.040
Well, what do you think
is going to happen?

00:03:23.040 --> 00:03:25.436
Well, I already said that
this is a strong acid

00:03:25.436 --> 00:03:26.513
right over here.

00:03:26.513 --> 00:03:30.212
So this is going to really
want to donate protons.

00:03:30.212 --> 00:03:32.648
It's really going to want
to donate this hydrogen,

00:03:32.648 --> 00:03:34.863
but not let the hydrogen
keep its electrons.

00:03:34.863 --> 00:03:36.834
So what's likely to happen here?

00:03:36.834 --> 00:03:39.617
Well, the both of these
electrons in this pair

00:03:39.617 --> 00:03:42.888
are going to be grabbed by this chlorine.

00:03:42.888 --> 00:03:45.511
And then this hydrogen ion,

00:03:45.511 --> 00:03:47.378
because its electron was grabbed,

00:03:47.378 --> 00:03:51.462
well this could be nabbed by
some water molecule passing by.

00:03:51.462 --> 00:03:54.073
Remember, in a real solution,

00:03:54.073 --> 00:03:55.718
it's not like they know what to do.

00:03:55.718 --> 00:03:57.039
They're just all bumping past each other.

00:03:57.039 --> 00:03:58.989
And based on how badly
they want to do things,

00:03:58.989 --> 00:04:00.919
these reactions happen.

00:04:00.919 --> 00:04:03.845
And so you can imagine this
lone pair right over here,

00:04:03.845 --> 00:04:07.461
well maybe it's able
to form a covalent bond

00:04:07.461 --> 00:04:08.437
with this hydrogen.

00:04:08.437 --> 00:04:10.428
And so what's going to happen?

00:04:10.428 --> 00:04:11.200
What's going to happen?

00:04:11.200 --> 00:04:12.500
And I'll draw it with just an arrow

00:04:12.500 --> 00:04:15.284
because this reaction favorably goes,

00:04:15.284 --> 00:04:17.193
very strongly goes to the right,

00:04:17.193 --> 00:04:19.835
because this is such a strong acid.

00:04:19.835 --> 00:04:21.643
Well, then you're going to be left with,

00:04:21.643 --> 00:04:24.345
you're gonna be left with,

00:04:24.345 --> 00:04:29.140
the chlorine is now going
to have its three lone pairs

00:04:29.140 --> 00:04:30.846
that it had before.

00:04:30.846 --> 00:04:33.813
And then it also grabbed
these two electrons

00:04:33.813 --> 00:04:34.869
right over here.

00:04:34.869 --> 00:04:37.633
It also grabbed those two
electrons right over there,

00:04:37.633 --> 00:04:39.089
so it gained an extra electron.

00:04:39.089 --> 00:04:40.863
It now has a negative charge.

00:04:40.863 --> 00:04:43.506
It is now the chloride anion.

00:04:43.506 --> 00:04:45.274
So it has a negative charge.

00:04:45.274 --> 00:04:47.407
And what about this water molecule?

00:04:47.407 --> 00:04:49.012
Well this water molecule,

00:04:49.012 --> 00:04:50.759
you have your oxygen,

00:04:50.759 --> 00:04:54.521
you have your hydrogens,
you have your hydrogens,

00:04:54.521 --> 00:04:56.284
but now you don't just have two hydrogens,

00:04:56.284 --> 00:04:58.072
you grabbed this hydrogen right over here.

00:04:58.072 --> 00:04:59.291
And maybe I'll do this hydrogen

00:04:59.291 --> 00:05:00.225
in a slightly different color

00:05:00.225 --> 00:05:03.171
so that you could keep track of it.

00:05:03.171 --> 00:05:05.813
You have this hydrogen right over there.

00:05:05.813 --> 00:05:09.988
And this lone pair, this
lone pair you can view it

00:05:09.988 --> 00:05:12.791
as now forming this covalent bond.

00:05:12.791 --> 00:05:14.376
You had your other two covalent bonds

00:05:14.376 --> 00:05:16.123
to the other two hydrogens.

00:05:16.123 --> 00:05:19.455
And then you still have this
lone pair right over here.

00:05:19.455 --> 00:05:22.950
You still have that lone pair
sitting right over there.

00:05:22.950 --> 00:05:24.536
And what just happened?

00:05:24.536 --> 00:05:27.257
Well, this water molecule
just gained a proton.

00:05:27.257 --> 00:05:30.395
This hydrogen did not
come with an electron.

00:05:30.395 --> 00:05:32.711
So if you just gain a proton, you are now,

00:05:32.711 --> 00:05:33.950
if you were neutral before,

00:05:33.950 --> 00:05:37.445
you are now going to
have a positive charge.

00:05:37.445 --> 00:05:38.826
So what just happened?

00:05:38.826 --> 00:05:43.013
You put hydrochloric
acid in a water solution,

00:05:43.013 --> 00:05:44.860
in an aqueous solution,

00:05:44.860 --> 00:05:49.086
this thing has donated a
proton to a water molecule.

00:05:49.086 --> 00:05:52.012
And so, what is the acid
and what is the base here?

00:05:52.012 --> 00:05:54.551
Well, when we look at
the reaction this way,

00:05:54.551 --> 00:05:59.203
we see that this is the acid,

00:05:59.203 --> 00:06:00.523
the hydrochloric acid,

00:06:00.523 --> 00:06:02.575
it's literally called hydrochloric acid.

00:06:02.575 --> 00:06:06.131
And here, water is acting as a base.

00:06:06.131 --> 00:06:09.138
Water is acting as a base.

00:06:09.138 --> 00:06:09.767
And as you could see,

00:06:09.767 --> 00:06:12.673
water can actually act
as an acid or a base.

00:06:12.673 --> 00:06:15.335
So, water is acting as a base.

00:06:15.335 --> 00:06:16.737
Now you might be saying, okay,

00:06:16.737 --> 00:06:19.418
this reaction goes strongly to the right,

00:06:19.418 --> 00:06:21.003
hey, but like you know, I could imagine

00:06:21.003 --> 00:06:25.073
in certain circumstances
where chloride might accept

00:06:25.073 --> 00:06:27.393
a proton because it has
this negative charge.

00:06:27.393 --> 00:06:28.226
And you would be right.

00:06:28.226 --> 00:06:30.604
This reaction goes strongly to the right,

00:06:30.604 --> 00:06:33.429
but once an acid has donated its proton,

00:06:33.429 --> 00:06:35.073
the thing that is left over,

00:06:35.073 --> 00:06:37.654
this is called a conjugate base.

00:06:37.654 --> 00:06:38.730
And I'll do the same color.

00:06:38.730 --> 00:06:42.489
So, this is the conjugate
base of hydrochloric acid.

00:06:42.489 --> 00:06:44.927
The chloride anion.

00:06:44.927 --> 00:06:49.927
Conjugate, conjugate base

00:06:50.026 --> 00:06:53.521
of hydrochloric acid.

00:06:53.521 --> 00:06:56.487
And this right over here
is the conjugate acid

00:06:56.487 --> 00:06:59.027
because you could imagine
this hydronium ion,

00:06:59.027 --> 00:07:01.303
this could, under the right circumstances,

00:07:01.303 --> 00:07:03.965
donate protons to other things.

00:07:03.965 --> 00:07:07.854
Donate a hydrogen without
donating electron to other things.

00:07:07.854 --> 00:07:12.710
And so this is actually
the conjugate acid of H2O.

00:07:12.710 --> 00:07:17.710
Conjugate acid of water,

00:07:18.837 --> 00:07:20.319
of a water molecule.

00:07:20.319 --> 00:07:23.976
And as we'll see, water can
act as an acid or a base.

00:07:23.976 --> 00:07:27.044
But this this gives you a
kind of a baseline of at least

00:07:27.044 --> 00:07:31.290
the Bronsted-Lowry definition
of acids and bases.

00:07:31.290 --> 00:07:32.957
And actually, one other
thing I want to add.

00:07:32.957 --> 00:07:36.107
In some books here, so
over here I said, hey,

00:07:36.107 --> 00:07:38.159
put this in an aqueous
solution you're gonna form

00:07:38.159 --> 00:07:41.430
some hydronium, sometimes
you'll see it written like this.

00:07:41.430 --> 00:07:43.909
And I'll just write it a
little bit, a little bit,

00:07:43.909 --> 00:07:46.896
sometimes you'll see it like this.

00:07:46.896 --> 00:07:48.622
So you have your hydrochloric acid,

00:07:48.622 --> 00:07:50.877
and I won't draw the details this time,

00:07:50.877 --> 00:07:52.807
in an aqueous solution.

00:07:52.807 --> 00:07:54.819
So it's in a solution of water.

00:07:54.819 --> 00:07:57.095
And they'll just draw the
reaction going like this,

00:07:57.095 --> 00:07:58.943
where they say hey,
you're gonna be left with,

00:07:58.943 --> 00:08:02.986
you're gonna be left
with some hydrogen ions,

00:08:02.986 --> 00:08:04.368
these protons.

00:08:04.368 --> 00:08:08.148
And you're going to be left with,

00:08:08.148 --> 00:08:09.128
and actually we could say

00:08:09.128 --> 00:08:11.462
it's gonna be in a aqueous solution,

00:08:11.462 --> 00:08:12.640
aqueous solution.

00:08:12.640 --> 00:08:16.222
And you're gonna be left
with some chloride anions.

00:08:16.222 --> 00:08:21.222
Some chloride anions and
it's in an aqueous solution.

00:08:21.458 --> 00:08:24.120
Now this isn't incorrect,
but it's important to realize

00:08:24.120 --> 00:08:25.582
what they're talking
about when they're talking

00:08:25.582 --> 00:08:27.439
about these hydrogen ions right over here.

00:08:27.439 --> 00:08:29.552
We know that if you have the hydrogen ions

00:08:29.552 --> 00:08:30.568
in an aqueous solution they don't just

00:08:30.568 --> 00:08:32.091
hang out by themselves.

00:08:32.091 --> 00:08:33.819
They get grabbed by a water molecule

00:08:33.819 --> 00:08:35.403
and they form hydronium.

00:08:35.403 --> 00:08:40.056
So, it's much more, I guess,
it's much more close to

00:08:40.056 --> 00:08:41.602
the actual of what's happening,

00:08:41.602 --> 00:08:44.099
is if you actually talk
about hydronium forming.

00:08:44.099 --> 00:08:45.501
As opposed to just the protons.

00:08:45.501 --> 00:08:47.329
'Cause these protons
in an aqueous solution,

00:08:47.329 --> 00:08:49.097
in a water solution,
they're gonna be grabbed

00:08:49.097 --> 00:08:52.185
by a water molecule to form hydronium.

00:08:52.185 --> 00:08:55.300
And that's why I did it
the way, this way up here.


Autoionization of water

WEBVTT
Kind: captions
Language: en

00:00:00.551 --> 00:00:03.175
- [Voiceover] I have two water
molecules right over here,

00:00:03.175 --> 00:00:04.858
and typically the water molecules, as they

00:00:04.858 --> 00:00:08.121
interact with each other,
they form these hydrogen bonds

00:00:08.121 --> 00:00:10.118
that's due to the polarity
of the water molecule.

00:00:10.118 --> 00:00:12.347
We've talked a lot about that, they slide

00:00:12.347 --> 00:00:14.146
past each other, these
hydrogen bonds give them

00:00:14.146 --> 00:00:16.526
all these neat properties of water.

00:00:16.526 --> 00:00:19.348
But chemistry is much
messier, than sometimes

00:00:19.348 --> 00:00:21.414
our diagrams or explanations show.

00:00:21.414 --> 00:00:23.121
There's all sorts of crazy interactions.

00:00:23.121 --> 00:00:24.317
All of these things are bumping

00:00:24.317 --> 00:00:26.256
into each other in all different ways.

00:00:26.256 --> 00:00:27.718
And not only are the molecules bumping

00:00:27.718 --> 00:00:29.425
in different ways, but any given moment,

00:00:29.425 --> 00:00:31.979
the electrons are jumping around and,

00:00:31.979 --> 00:00:34.278
on average, they might spend more time,

00:00:34.278 --> 00:00:36.728
they might spend more
time around the oxygen

00:00:36.728 --> 00:00:39.533
forming a partially
negative charge at that end,

00:00:39.533 --> 00:00:41.758
and then a partially positive charge near

00:00:41.758 --> 00:00:44.219
the hydrogens, because the
hydrogens are having their

00:00:44.219 --> 00:00:46.089
electrons hogged away from them.

00:00:46.089 --> 00:00:48.689
In fact this is what
forms the hydrogen bonds.

00:00:48.689 --> 00:00:51.150
But there's always
constantly change there.

00:00:51.150 --> 00:00:52.451
Because they're all just jumping around.

00:00:52.451 --> 00:00:54.784
It's all very probabilistic.

00:00:54.784 --> 00:00:57.513
And so you can imagine, under
just the right conditions,

00:00:57.513 --> 00:01:01.925
one oxygen or one water
molecule, might just

00:01:01.925 --> 00:01:04.688
graze this water molecule
in the right way,

00:01:04.688 --> 00:01:08.449
that these electrons,
that these electrons,

00:01:08.449 --> 00:01:13.449
get close enough to nab,
to nab this hydrogen.

00:01:13.523 --> 00:01:15.857
But it doesn't nab the entire hydrogen.

00:01:15.857 --> 00:01:18.492
It doesn't nab the
nucleus and the electron,

00:01:18.492 --> 00:01:21.240
and a typical hydrogen atom,
a typical hydrogen atom,

00:01:21.240 --> 00:01:22.424
actually let me draw it.

00:01:22.424 --> 00:01:26.116
A typical hydrogen atom is just a proton,

00:01:26.116 --> 00:01:27.892
is just a proton in the nucleus.

00:01:27.892 --> 00:01:30.040
Actually the most typical
isotope of hydrogen

00:01:30.040 --> 00:01:33.488
has no neutron, so it's just
a proton in the nucleus.

00:01:33.488 --> 00:01:36.054
And an electron orbiting around it.

00:01:36.054 --> 00:01:38.411
So this right over here is positive,

00:01:38.411 --> 00:01:39.990
actually maybe I'll draw it that way,

00:01:39.990 --> 00:01:42.474
you have a positive
proton, and then you have

00:01:42.474 --> 00:01:45.957
a negative electron, you
have a negative electron

00:01:45.957 --> 00:01:46.654
orbiting around it.

00:01:46.654 --> 00:01:48.720
Actually it's more of a orbital.

00:01:48.720 --> 00:01:51.493
So it's really this electron
is jumping all around it.

00:01:51.507 --> 00:01:53.687
But you could imagine,
these electrons in this

00:01:53.687 --> 00:01:56.079
covalent bond, they were already being,

00:01:56.079 --> 00:01:57.983
these we already being hogged,

00:01:57.983 --> 00:02:00.259
these were already being
hogged by this oxygen,

00:02:00.259 --> 00:02:01.617
in fact that's what was forming this

00:02:01.617 --> 00:02:03.347
partial negative charge over here,

00:02:03.347 --> 00:02:05.947
and the partial positive charge over here.

00:02:05.947 --> 00:02:07.387
So these would be attracted to this

00:02:07.387 --> 00:02:08.687
partial positive charge.

00:02:08.687 --> 00:02:10.150
Remember there, you
have a partial negative

00:02:10.150 --> 00:02:12.220
charge over here, this is
actually what's forming

00:02:12.220 --> 00:02:13.416
the hydrogen bond.

00:02:13.416 --> 00:02:16.620
And it actually could bond
to the hydrogen proton,

00:02:16.620 --> 00:02:18.756
while both of these
electrons, including one

00:02:18.756 --> 00:02:20.324
of these electrons that used to be part of

00:02:20.324 --> 00:02:21.519
this hydrogen, or you could consider

00:02:21.519 --> 00:02:23.052
used to be part of that hydrogen,

00:02:23.052 --> 00:02:27.162
are nabbed, are nabbed by this oxygen.

00:02:27.162 --> 00:02:28.857
And in this circumstance,
and I'm not saying

00:02:28.857 --> 00:02:30.285
that this happens all the time,

00:02:30.285 --> 00:02:32.189
but under just the right conditions, this

00:02:32.189 --> 00:02:35.161
actually can happen,
and what would result,

00:02:35.161 --> 00:02:38.749
so let me, what result is, this thing

00:02:38.749 --> 00:02:41.187
over here, instead of just being a neutral

00:02:41.187 --> 00:02:43.985
water molecule, would look like this.

00:02:43.985 --> 00:02:46.516
So you have your oxygen, you have,

00:02:46.516 --> 00:02:48.396
not only your two hydrogens now,

00:02:48.396 --> 00:02:50.619
you now have a third hydrogen.

00:02:50.619 --> 00:02:52.906
You now have a third hydrogen.

00:02:52.906 --> 00:02:55.321
So you have these two covalent bonds,

00:02:55.321 --> 00:02:58.618
these two covalent bonds, this lone pair.

00:02:58.618 --> 00:03:01.521
And now this lone pair,
which I have circled in blue,

00:03:01.521 --> 00:03:05.178
is now being shared with
this hydrogen proton.

00:03:05.178 --> 00:03:06.687
This electron right over
here of the hydrogen

00:03:06.687 --> 00:03:08.615
got nabbed by this oxygen.

00:03:08.615 --> 00:03:11.053
So now you've formed
another covalent bond.

00:03:11.053 --> 00:03:12.945
And now this character over here,

00:03:12.945 --> 00:03:15.047
he's lost the hydrogen proton, but he's

00:03:15.047 --> 00:03:16.985
kept all of the electrons.

00:03:16.985 --> 00:03:19.424
So this character over
here's gonna look like this.

00:03:19.424 --> 00:03:21.646
You're gonna have your oxygen,

00:03:21.646 --> 00:03:24.345
and now it's only going to only be bonded

00:03:24.345 --> 00:03:28.919
to one hydrogen, only
bonded to one hydrogen.

00:03:28.919 --> 00:03:31.694
Has these two original lone pairs.

00:03:31.694 --> 00:03:34.318
These two original lone
pairs right over here.

00:03:34.318 --> 00:03:36.419
And then took both of the electrons

00:03:36.419 --> 00:03:38.579
from this covalent bond.

00:03:38.579 --> 00:03:41.191
And took both of the electrons
from this covalent bond.

00:03:41.191 --> 00:03:43.095
And so it has another lone pair.

00:03:43.095 --> 00:03:45.858
So this molecule gained just a proton

00:03:45.858 --> 00:03:47.623
without getting any electrons.

00:03:47.623 --> 00:03:49.260
So if you do that, you're
now going to have a

00:03:49.260 --> 00:03:51.826
net positive charge
for this one over here.

00:03:51.826 --> 00:03:54.484
And this molecule over
here, actually let me,

00:03:54.484 --> 00:03:56.818
let me, ugh, let me just write it.

00:03:56.818 --> 00:03:58.083
I wanna write it a little bit neater.

00:03:58.083 --> 00:03:59.953
And this molecule over here, so we have

00:03:59.953 --> 00:04:03.154
this molecule plus this one, this one

00:04:03.154 --> 00:04:05.953
lost a proton, without any other changes.

00:04:05.953 --> 00:04:08.693
So it now has a negative charge.

00:04:08.693 --> 00:04:10.865
So just like that, you
went from two neutral

00:04:10.865 --> 00:04:13.791
water molecules, to two ions.

00:04:13.791 --> 00:04:15.323
And these ions, this one over here,

00:04:15.323 --> 00:04:17.053
the one on the left, the one that is now

00:04:17.053 --> 00:04:22.053
H three O, H three O, H three O,

00:04:23.253 --> 00:04:26.387
and it now has a positive charge,

00:04:26.387 --> 00:04:28.791
positive charge, actually I put that O

00:04:28.791 --> 00:04:30.056
in a different color.

00:04:30.056 --> 00:04:34.155
H three, H three O.

00:04:34.155 --> 00:04:38.125
It's a positive charge, this
is called the "hydronium ion."

00:04:38.125 --> 00:04:42.328
Hydronium, hydronium.

00:04:42.328 --> 00:04:47.053
And this one over here, that is OH minus,

00:04:47.053 --> 00:04:52.053
so it's OH, O, let me
get the colors right.

00:04:53.056 --> 00:04:57.642
OH minus.

00:04:57.642 --> 00:04:59.650
This is called the
"hydroxide ion," or since

00:04:59.650 --> 00:05:01.994
it's negative you can
just call it an "anion."

00:05:01.994 --> 00:05:06.847
I'll just write "hydroxide," hydroxide,

00:05:06.847 --> 00:05:09.390
hydroxide ion right over there.

00:05:09.390 --> 00:05:11.012
So you have this water
and it's just kind of

00:05:11.012 --> 00:05:12.789
automatically under the
right circumstances,

00:05:12.789 --> 00:05:14.658
this isn't happening a lot, but under the

00:05:14.658 --> 00:05:17.444
right circumstances, you could have one

00:05:17.444 --> 00:05:19.081
of the water molecules nabbing just

00:05:19.081 --> 00:05:21.624
the hydrogen proton, from
another water molecule.

00:05:21.624 --> 00:05:23.760
And that water molecule
is gonna keep both of the

00:05:23.760 --> 00:05:25.873
electrons, and then they ionize.

00:05:25.873 --> 00:05:28.218
They have autoionized,
and this phenomenon,

00:05:28.218 --> 00:05:31.539
this is called "the
autoionization of water."

00:05:31.539 --> 00:05:33.989
Let me write that down,
it's a nice big word.

00:05:33.989 --> 00:05:37.506
Autoionization.

00:05:37.506 --> 00:05:41.988
Autoionization of, of water.

00:05:41.988 --> 00:05:43.927
And I really want to make
it clear what happens.

00:05:43.927 --> 00:05:46.260
This hydrogen over here,
that you can imagine

00:05:46.260 --> 00:05:48.547
at first was a proton and an electron,

00:05:48.547 --> 00:05:49.958
the typical isotope of hydrogen actually

00:05:49.958 --> 00:05:51.455
does not have a neutron.

00:05:51.455 --> 00:05:54.218
But then this electron got swiped.

00:05:54.218 --> 00:05:57.620
This electron, this electron
was part of this bond

00:05:57.620 --> 00:05:59.280
and it gets swiped away, and so all you're

00:05:59.280 --> 00:06:01.649
left is with this proton, and this proton

00:06:01.649 --> 00:06:03.623
goes to this other water molecule,

00:06:03.623 --> 00:06:06.153
giving that a positive charge.

00:06:06.153 --> 00:06:08.325
And so you might say,
"Well how frequently would

00:06:08.325 --> 00:06:11.750
"I find hydronium ions in water?"

00:06:11.750 --> 00:06:13.851
Well the concentration,
let me actually draw

00:06:13.851 --> 00:06:15.349
a little tub of water
here, let's say this is a

00:06:15.349 --> 00:06:16.811
liter of water.

00:06:16.811 --> 00:06:21.781
This is a liter, this is a liter of water.

00:06:21.781 --> 00:06:25.751
The concentration of
hydronium in typical water,

00:06:25.751 --> 00:06:28.816
the concentration of H three O,

00:06:28.816 --> 00:06:31.219
the concentration of H
three O in typical water,

00:06:31.219 --> 00:06:32.520
and you put brackets around something

00:06:32.520 --> 00:06:34.215
to denote "concentration," is

00:06:34.215 --> 00:06:38.360
one times ten to the negative seven molar.

00:06:38.360 --> 00:06:40.426
And molar, this just
means "moles per liter."

00:06:40.426 --> 00:06:41.181
This is the same thing as

00:06:41.181 --> 00:06:45.186
one times ten to the negative seven moles,

00:06:45.186 --> 00:06:47.090
moles per liter.

00:06:47.090 --> 00:06:48.925
And now you might be saying,
"Well, what's a mole?"

00:06:48.925 --> 00:06:50.225
Well I encourage you to watch the video on

00:06:50.225 --> 00:06:51.850
what a mole is, but a mole is a quantity.

00:06:51.850 --> 00:06:53.180
It's like saying, "a dozen."

00:06:53.180 --> 00:06:54.620
But it's a much larger, a dozen is equal

00:06:54.620 --> 00:06:55.792
to 12 of something.

00:06:55.792 --> 00:06:58.553
A mole is roughly equal
to, let me write it.

00:06:58.553 --> 00:07:00.956
A mole is approximately equal to

00:07:00.956 --> 00:07:04.358
6.02 times ten to the 23rd.

00:07:04.358 --> 00:07:07.458
Ten to the 23rd of something.

00:07:07.458 --> 00:07:09.246
And you're typically
talking about molecules.

00:07:09.246 --> 00:07:13.288
A mole of a substance means approximately

00:07:13.288 --> 00:07:15.587
6.022, it actually keeps going, times

00:07:15.587 --> 00:07:19.024
ten to the 23rd molecules of that thing.

00:07:19.024 --> 00:07:21.403
So you might say, "Hey, one
times ten to the negative seven

00:07:21.403 --> 00:07:23.793
"times 6.02 times ten to the 23rd,

00:07:23.793 --> 00:07:27.021
"that would still get
us," well let's see, this,

00:07:27.021 --> 00:07:27.950
let me actually, let me write it down.

00:07:27.950 --> 00:07:30.318
One times ten to the negative seven

00:07:30.318 --> 00:07:35.308
moles per liter, times,

00:07:35.308 --> 00:07:37.978
times, I'll do it this way.

00:07:37.978 --> 00:07:40.721
Times six, I'll just go
with six, since we're

00:07:40.721 --> 00:07:42.114
gonna go approximately.

00:07:42.114 --> 00:07:47.114
So approximately, six
times ten to the 23rd.

00:07:48.479 --> 00:07:53.479
Six times 23rd molecules,
molecules per mole.

00:07:53.959 --> 00:07:56.014
Molecules per mole, well these two would

00:07:56.014 --> 00:07:58.452
cancel out, and you would
multiply these two numbers,

00:07:58.452 --> 00:08:01.053
you would get six times, let's see.

00:08:01.053 --> 00:08:03.560
Ten to the negtive seven
times ten to the 23rd,

00:08:03.560 --> 00:08:06.184
that's still gonna be
ten to the 16th power,

00:08:06.184 --> 00:08:08.158
molecules per liter.

00:08:08.158 --> 00:08:11.153
Molecules per liter, so
your first reaction is,

00:08:11.153 --> 00:08:12.256
"Oh my God!"

00:08:12.256 --> 00:08:14.845
"I'm gonna have six times,"
or roughly, I'll say roughly.

00:08:14.845 --> 00:08:17.423
"Approximately six times ten to the 16th

00:08:17.423 --> 00:08:18.990
"molecules of hydronium in this?"

00:08:18.990 --> 00:08:21.022
"That's a lot, we should
see it all the time."

00:08:21.022 --> 00:08:22.461
But we have to remind ourselves.

00:08:22.461 --> 00:08:26.188
There's just a lot of molecules
of water in there as well.

00:08:26.188 --> 00:08:29.253
In fact, a liter of water is roughly,

00:08:29.253 --> 00:08:34.253
so one liter of H two O, contains,

00:08:34.884 --> 00:08:39.884
contains approximately 56,

00:08:39.888 --> 00:08:44.888
56 moles, moles of H two O.

00:08:46.587 --> 00:08:48.212
So one way to think about it is,

00:08:48.212 --> 00:08:50.523
"I have one, I have one times," and if I'm

00:08:50.523 --> 00:08:52.055
thinking about a liter of water,

00:08:52.055 --> 00:08:53.890
I have, I'll do it over here,

00:08:53.890 --> 00:08:57.483
"I have one times ten
to the negative seven

00:08:57.483 --> 00:09:02.483
"moles of, moles of H three O for every,

00:09:05.018 --> 00:09:10.018
"for every 56 moles, for every 56 moles,

00:09:11.461 --> 00:09:14.306
"moles of H two O."

00:09:14.306 --> 00:09:16.616
So if you look at this ratio,
then you start to appreciate.

00:09:16.616 --> 00:09:19.495
The ratio of one times ten
to the negative seven to 56.

00:09:19.495 --> 00:09:21.190
Let me do it down here.

00:09:21.190 --> 00:09:22.920
So this is the same thing as,

00:09:22.920 --> 00:09:27.460
one times ten to the negative seven to 56,

00:09:27.460 --> 00:09:29.886
is the same thing as,
let's just multiply both

00:09:29.886 --> 00:09:32.882
side times, or the numerator
and the denominator,

00:09:32.882 --> 00:09:34.716
times ten to the seventh.

00:09:34.716 --> 00:09:38.988
So if we do that, this
is the same thing as one,

00:09:38.988 --> 00:09:43.988
one, the ratio of
hydronium to regular water,

00:09:44.074 --> 00:09:47.255
to H two O is gonna be one
to, let's see if I multiply

00:09:47.255 --> 00:09:49.960
56, times ten to the
seventh, I'm gonna have

00:09:49.960 --> 00:09:53.083
five, let me get, write
in that same color.

00:09:53.083 --> 00:09:56.554
I'm gonna have five six,
then I'm gonna have,

00:09:56.554 --> 00:09:58.853
I'm gonna throw seven
zeros at the end of it.

00:09:58.853 --> 00:09:59.991
Let me do that.

00:09:59.991 --> 00:10:03.660
One, two, three, four, five, six, seven.

00:10:03.660 --> 00:10:07.491
So the ratio of hydronium
to regular H two O

00:10:07.491 --> 00:10:10.719
is one for ever five
hundred and sixty million.

00:10:10.719 --> 00:10:12.518
So even though you might
say, "Oh wow, look."

00:10:12.518 --> 00:10:15.421
"We're gonna have a
huge number of molecules

00:10:15.421 --> 00:10:17.754
"of hydronium in this liter of water."

00:10:17.754 --> 00:10:20.444
For every one of them, you actually have

00:10:20.444 --> 00:10:25.444
roughly five hundred sixty
million molecules of H two O.

00:10:25.852 --> 00:10:28.917
So that should give you
an appreciation for the

00:10:28.917 --> 00:10:31.286
fact that this isn't that typical.

00:10:31.286 --> 00:10:33.341
In fact, you're gonna
see this much more often

00:10:33.341 --> 00:10:34.653
than you see this over here.

00:10:34.653 --> 00:10:37.393
In fact, if you wanted
to make these arrows

00:10:37.393 --> 00:10:40.458
kind of show which direction
the equilibrium sits in,

00:10:40.458 --> 00:10:43.140
it's actually much further,
it's actually much further

00:10:43.140 --> 00:10:43.755
to the left.

00:10:43.755 --> 00:10:45.659
So we could make this arrow much bigger.

00:10:45.659 --> 00:10:46.855
But it also gives you an appreciation

00:10:46.855 --> 00:10:49.084
for just how many
molecules you have sitting

00:10:49.084 --> 00:10:53.107
in a liter, in a liter of water.