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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