Reminder: 1 mol of anything e.g. Oxygen, carbon, dollars, toys, etc. is 6.02 x 10 23

Let’s look at this pile of carbon in the form of charcoal. I bet you there is a bunch of carbon moles in there. Let’s see how much.

Now, this clump represents one mole. Can you estimate how many do you see in the whole bunch? Well, it’s hard to visualize. Let’s do some math. Since this is 1 mole, that means it weighs g. Why? Because, according to the periodic table, 1 mole of Carbon weighs g. Well, how many moles are present in this whole bunch? Let’s weigh it first.

0.00 g12.01 g 6.02 x 10 23

0.00 g So, we weigh the whole bunch and it turns out to be g g

1 mol ? mol

So, there are two ways to solve this problem: a)Use proportions b)Use the n= m / mMm a)Use proportions: Since1 mol of C=12.01 g ? mol=15.50 g ? mol=1 mol of Cx15.50 g g =1.29 mol

b)Let’s use the formula n= m / mMm Step 1: What do we have? m: g mMm: g/mol N: ? Step 2: You can use a triangle mn: m. mMm n x mMmn: g g/mol n: 1.29 mol

Another example: let’s say there are 4 moles of water in this beaker. How many grams would that be?

Well, there are a couple of steps. We are trying to find the mass of 4 moles of water, we need the molar mass of water. Step 1: Find molar mass H 2 O: 2(1)+16=18 g/mol Step 2: Let’s find the mass, I’ll use the proportions method 1 mol of H 2 O=18 g 4 mol of H 2 O=? g ? g=4 mol of H 2 Ox18 g/mol 1 mol of H 2 O ? g=72 g What about the number of molecules?

Well, for the number of molecules, let’s see what happens. 1 mol of H 2 O=6.02x10 23 molecules of H 2 O 4 mol of H 2 O=? molecules ? molecules=4 mol of H 2 O x (6.02 x molecules of H 2 O) 1 mol of H 2 O =2.408x molecules of H 2 O

Okay, solve the following problems: a)How many moles of Ca(OH) 2 are present in a 200 g sample of Ca(OH) 2 ? b)How many molecules of MgF 2 are present in a 100 g sample of MgF 2 ?