Unit 2 Section C Mole to Gram Conversions

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Unit 2 Section C
Mole to Gram Conversions
(or How to Count Formula Units or Molecules by Weighing)
Example 1: How many moles are present in 352 g of iron(III) oxide, Fe2O3?
Step 1: Calculate the molar mass of iron (III) oxide.
Fe: 2 x 55.85 g = 111.7g
O: 3 x 16.00 g = 48.00 g
molar mass = 159.7 g Fe2O3 = 1 mole Fe2O3
This can be expressed in two ways as a conversion factor (or a proportion). It is either:
a. 159.7 g of Fe2O3 contains 1 mole or:
159.7 g Fe2O3
1 mole Fe2O3
b. 1 mole of Fe2O3 contains 159.7 g or:
1 mole Fe2O3
159.7 g Fe2O3
Step 2: Arrange a proportion to solve for the unknown (x) value:
352 g Fe 2O 3
x mol Fe 2O 3
=
159.7 g Fe 2O 3
1 mol Fe 2O 3
x = 2.20 mole Fe2O3
Example 2: What mass is present in 1.43 moles of magnesium hydroxide, Mg(OH)2?
€
Step 1:
Calculate the molar mass of magnesium hydroxide.
Mg: 1 x 24.31g = 24.31 g
O: 2 x 16.00 g = 32.00 g
H: 2 x 1.008 g = 2.02 g
molar mass = 58.33 g Mg(OH)2 = 1 mole Mg(OH)2
Step 2: Arrange a proportion to solve for the unknown (x) value:
1.43 mol Mg(OH) 2
1 mol Mg(OH)2
=
x g Mg(OH) 2
58.33 g Mg(OH) 2
x = 83.41 g Mg(OH)2
Fe2Osubstance;
3
First, calculate the molar mass of the
second, use the conversion factor set up
Calculate the following.
a proportion to convert from grams  moles or from moles  grams.
€ 1. How many grams equal 3.5 mol of Na2S?
Cont. on back side…
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2. How many grams equal 6.3 mol of N2?
3. How many moles equal 84.6 g of NaCl?
4. How many moles equal 564 g of C12H22O11?
5. How many grams equal 3.95 mol of CuFeS2?
6. How many moles equal 0.985 g of Cu2CO3(OH)2 ?
7. How many grams equal 36.5 mol of Cu3(CO3)2(OH)2?