Molar Mass of Compounds and Conversions
Definition of Molar Mass of Compounds
The molar mass of any substance is the mass in grams of 1 mole of the substance. The molar mass of a compound is obtained by summing the molar masses of the component atoms.
1 mol of SO2 = 1 mol of S atoms + 2 mol of O atoms
= 1 (32.07 g) + 2 (16.00 g)
= 64.07 g
1 mol of of CaCO3 = 1 mol of Ca atoms + 1 mol of C atoms + 3 mol of O atoms
= 1 (40.08 g) + 1(12.01g) + 3(16.00g)
= 100.09 g
1 mol of Fe(OH)3 = 1 mol of Fe atoms + 3 mol of O atoms + 3 mol of H atoms
= 1(55.85 g) + 3(16.00 g) + 3(1.008 g)
= 106.87 g
Conversion between Molar Mass of Compounds to Moles
Problem: A sample of Na2SO4 with a mass of 300.0 g represents what number of moles of sodium sulfate?
Step 1: Calculate the molar mass of the compound
1 mol of Na2SO4 = 2 mol of Na atoms +
1 mol of S atoms +
4 mol of O atoms
= 2( 22.99 g) +
1 (32.07 g) +
4(16.00 g)
= 96.07 g
Step 2: Use the molar mass of the compound as a fraction to cross cancel out units
300.0 g Na2SO4 x 1 mol Na2SO4
96.07 g
Step 3: Solve the equation.
= 3.122 mol of Na2SO4
Exercises
1. Convert 7.14 mol K2O = _________ g K2O
2. Convert 0.189 mol Ca(OH)2 = _________ g Ca(OH)2
3. Convert 4.89 g O3 = ___________ molecules O3
4. Convert 6.12 mol Cu(NO3)2 = __________ g Cu(NO3)2
5. Convert 42.3 g NO2 = __________ moles NO2
6. Convert 9.14 mol PCl5 = __________ molecules PCl5
7. Convert 72.8 g CO = __________molecules CO
8. Convert 1.42 mol Mg(NO3)2 = ____________ g Mg(NO3)2
9. Convert 12.4 mol CaF2= ____________ g CaF2
10. Convert 14.3 g NaCl = ___________ mol NaCl
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