 In this video we’re gonna convert moles
to mass and vice versa using two examples. We can inter-convert
from moles to mass and from mass to moles using the molar mass of that
substance. In order to perform this calculation we’ll first need to know how
to calculate molar mass. I’ll link the video on the top if you need a refresher.
Let’s try out a couple of questions to see how we can convert between these two
things, moles and mass. Let’s look at our first question. It gives us 0.245 moles and it’s asking us to find the mass of zinc. We’re gonna use
dimensional analysis method to solve this, so, we write out what we need to
find which is the mass of zinc equals what the question gives which is 0.245 moles and then we place a multiple sign and draw a line
across. Place what we want to get rid of at the bottom which is moles and then it
will cancel out like that and then we place what we need to find on top which
is the grams of zinc. We look at the atomic mass of zinc in the periodic
table and we get 65.39. So we place that next to the grams
and since it’s the molar mass is the mass for one mole that means it’s one
next to the mole. So, we do the math, 0.245 times 65.39 gives us 16.0 grams. If you don’t like solving
using this method just remember if you’re given moles and you need to find
mass, simply multiply the given number with the molar mass. Moving on to our
next and final question. This question is the reverse of the first question. It
gives us the mass and it wants us to find out moles. We’re gonna use the same
method, so, we’re gonna start by writing out what we need to find and then equals
what we’re given 392 grams and times draw a line across and then we place
grams at the bottom so that we can cancel them out. And then we place mol on top
because that’s what we need to find. Okay. Now it’s time to fill in the numbers
since we’re using molar mass which means its the mass for one mole, so, we’ll place
one next to mole and then we need to calculate the molar mass of CCl4 and
that’s 12 plus 4 times 35.45. 12 for carbon. 35.45 for chlorine which turns out to be 153.8 grams. We
take 392 times 1 and divided by 153.8 and we get 2.55 mols. Don’t forget to include the unit mol.
Again if you’re not into this way of solving, all you have to remember is in
going from grams to moles all you have to do is you divide the given mass with
the molar mass of the compound. To recap, from the two questions we’ve worked on,
when going from moles to mass we multiply with the molar mass and in
going from mass to moles we divide the molar mass. I hope the video helped you
out somehow. Do subscribe and thanks for watching!