Reminder: 1 mol of anything e.g. Oxygen, carbon, dollars, toys, etc. is 6.02 x 10 23
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Transcript of Reminder: 1 mol of anything e.g. Oxygen, carbon, dollars, toys, etc. is 6.02 x 10 23
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Reminder: 1 mol of anything e.g. Oxygen, carbon, dollars, toys, etc. is 6.02 x 1023
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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.
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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 12.01 g. Why? Because, according to the periodic table, 1 mole of Carbon weighs 12.01 g. Well, how many moles are present in this whole bunch? Let’s weigh it first.
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0.00 g12.01 g6.02 x 1023
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0.00 g
So, we weigh the whole bunch and it turns out to be 15.50 g.
15.50 g
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1 mol
? mol
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So, there are two ways to solve this problem:
a) Use proportions
b) Use the n= m / mMm
a) Use proportions:
Since 1 mol of C = 12.01 g
? mol = 15.50 g
? mol = 1 mol of C x 15.50 g12.01 g
= 1.29 mol
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b) Let’s use the formula n= m / mMm
Step 1: What do we have?
m: 15.50 g
mMm: 12.01 g/mol
N: ?
Step 2: You can use a triangle
m n: m . mMm
n x mMm n: 15.50 g 12.01 g/mol
n: 1.29 mol
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Another example: let’s say there are 4 moles of water in this beaker. How many grams would that be?
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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
H2O: 2(1) + 16 = 18 g/mol
Step 2: Let’s find the mass, I’ll use the proportions method
1 mol of H2O = 18 g
4 mol of H2O = ? g
? g = 4 mol of H2O x 18 g/mol 1 mol of H2O
? g = 72 g
What about the number of molecules?
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Well, for the number of molecules, let’s see what happens.
1 mol of H2O = 6.02 x 1023 molecules of H2O
4 mol of H2O = ? molecules
? molecules = 4 mol of H2O x (6.02 x 1023 molecules of H2O) 1 mol of H2O
= 2.408 x 1024 molecules of H2O
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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 MgF2 are present in a 100 g sample of MgF2?