Hello everyone!
Welcome to Lecture number 3.
Youíre moving right along, so congratulations.
This one is going to be on measurement tools
that we are going to use in the laboratory.
And the first oneÖyesÖis the ruler.
Now, I know you have all used rulers before,
but you will not believe how many times I
get people measuring in inches and not by
the metric system in cm!
On a ruler, you will see two sides.
You will see the inch side, and thatís usually
labeled, and you will have the side with the
millimeters on it.
Now a millimeter is each one of these little
lines.
Ok, and then you have a big line on the millimeter
side which has the numbers and this is one
centimeter.
OkÖso when you are measuring PLEASE, PLEASE
PLEASE , because it is science class, use
the millimeter side.
Ok.
I donít want to hear if something is 8 centimeters,
I donít want to see on your paper that itís
3! Itís not 3, itís 8! Ok, so make sure
youíre using the right side.
Letís say you wanted to take the mass of
this little blue cubeÖisnít he cute.
So if it is a solid object you would put it
onto the balance.
You want to make sure that indeed the balance
is on.
If you do not see numbers on the digital balance
then the digital balance is not on and you
want to push this button.
Once it comes on it will usually have some
zeroes and itís usually measured in grams.
So you would take your cube, put it onto the
balance, and you would getÖoh I donít knowÖ
letís say itís a two gram cube.
So it would give you the reading and you would
record that in grams on the sheet.
NowÖlet me just get rid of this... letís
say it wasnít something as lovely as a cube.
Maybe you want to measure the mass of a liquid.
You kind of just canít pour that all over
the balance, you will ruin it.
So you want to put it in this lovely cup.
So I have this little clear cup here and Iím
going to put that on the balance, but I donít
want to know the mass of the cup.
Itís going to throw off my results.
I need to get rid of that mass from my measurements.
So, they have this little buttonÖsometimes
itís called zero on a balance, sometimes
itís called tare.
Youíre gonna press that buttonÖ so letís
say the cup was ÖI donít know, Iím just
making something upÖlike half a gram.
Youíre going to push the button and it will
get rid of that mass for you.
Itís quite handy.
And then you can put whatever you want inside
it to see what the mass is.
So letís say I put some liquid in thereÖ
OkÖand the balance read out 1.7 grams.
Sometimes youíll be using weighing papers,
so youíll put a paper on here and it would
give you the massÖand you would press tare
to get rid of the mass of that paper and you
would put your powder on it.
And then it would give you the mass of that
powder.
Ok, so the next measurement tool that you
have is the graduated cylinder, and when you
measure with a graduated cylinder you want
to makes you measure the liquid at the meniscus
which is this curve that the water makes due
to cohesion and adhesion of the liquid.
So molecules are attracting each otherÖ weíre
not really going to go into depth.
But, it forms this curve and what you want
to do is you want to read this at the bottom
of the curve of the liquid.
So that would be right here.
SO you do not want to read that at the top.
You want to read it at the curveÖ OKÖthe
meniscus.
So if we took a look we have six here and
we have seven here so that looks to be aboutÖah
weíre eyeballing itÖabout 6.7 milliliters.
Ok, so beakers and flasks.
So here we have a normal, everyday beaker
and we have an Erlenmeyer flask which is my
favorite kind just because it has a cool name.
And theseÖsuper easyÖyou just read them
where the line of the liquid stops.
You want to make sure you have this still
and youíre not tilting it, so both of these
are at 100 mL.
Microscope Video
