Tip:
Highlight text to annotate it
X
Mole to particles calculations. In this video we're going to look at the steps that we go
through to convert any unit that's already in moles to particles using Avogadro's number.
So a few quick reminders here. First we need to remember that one mole of any substance,
which could be an element or a compound or a molecule, has exactly 6.022 x 10^23 particles
per that one mole. You'll notice I have particles, slash atoms, slash molecules. It really depends
on the substance that you are dealing with. If you're dealing with an element, then we
use atoms to indicate the particle in question. If we're dealing with something that's covalently
bonded (remember that's when electrons are shared between 2 nonmetals) then we have a
molecule. And particle we'll use for anything that's ionically bonded, electrons are given
and taken between a metal and a nonmetal or between a metal and a polyatomic ion. Once
again, we'll use dimensional analysis to convert back an forth from moles of that substance
to particles or atoms or molecules. And then the last is my ever-present remind to pay
attention to your significant figures and your labels. Two example problems that we
will look at for this particular type of conversion. The first one says how many particles are
in 2.3 moles of sodium chloride. I've changed the color and underlined "particles" as an
indication to the unit we are converting to. So we're going to take our 2.3 moles as our
starting point, and convert moles to particles. So using dimensional analysis, set up your
brackets. Moles will need to go on the bottom. My new unit will go on top, and that happens
to be particles. So I know that my relationship between moles and particles is one mole equals
6.02 x 10^23 particles. Multiply across the top, divide by my one mole in the bottom,
give me an answer of 1.384 x 10^24. We need to look at significant figures. 2.3 gives
me 2 sig figs, so my answer will actually be 1.4 times 10^24 particles. Second problem
then. How many moles contain 13.4 x 10^24 molecules of oxygen. Moles is the item that
I have in a different color and underlined, so that is the unit I'm looking to find. My
starting point will be 13.4 x 10^24 molecules. So I'll go ahead and write that into my conversion
factor. Which means that my molecules need to go opposite, or in the denominator of the
large fraction. I'm converting to moles, so once again I know that one mole is equal to
6.02 x 10^23, so this is Avogadro's number again. Molecules cancel. Moles is the unit
that I am searching for, that I'm trying to find. So once everything crosses out an I'm
left with moles in the numerator, I can go ahead and do my mat. The answer to this equation,
rounded to 3 significant figures will be 22.6 moles. A couple little trouble-shooting items
before I close this video. When you are multiplying be a large exponent (the x 10^24), there are
a couple of different ways to do that on your calculator. So if find that your answer is
not matching up with the answers I have in the video, or not matching up with the questions
we have on the worksheet keys, it's probably an "order of operations" issue with your graphing
calculators. The second item, Avogadro's number (6.022 x 10^23) can be saved in your graphing
calculators, and if need help with the if you'd like to do that, let myself or Mrs.
Meyer know because it's just a little timesaver and ensures that you're always entering that
number correctly when you're doing these calculations. Good luck with the problems, let me know if
you have any questions.