6.2 Molar Mass
Notes
The molar mass is the mass of 1 mole of a substance, in g/mol. It equals the atomic or formula mass from the periodic table.
- For an element, read the atomic mass: 1 mol C = 12.01 g.
- For a compound, add the masses of all atoms. Multiply subscripts through parentheses.
- $\text{H}_2\text{O}$: $2(1.01) + 16.00 = 18.02$ g/mol.
- $\text{Ca(OH)}_2$: $40.08 + 2(16.00 + 1.01) = 74.10$ g/mol.
- $\text{C}_6\text{H}_{12}\text{O}_6$: $6(12.01) + 12(1.01) + 6(16.00) = 180.18$ g/mol.
Practice
What is the molar mass of $\text{CO}_2$? (C = 12.01, O = 16.00)
$12.01 + 2(16.00) = 44.01$ g/mol. 28.01 forgets the second oxygen.
What is the molar mass of $\text{H}_2\text{SO}_4$? (H = 1.01, S = 32.07, O = 16.00)
$2(1.01) + 32.07 + 4(16.00) = 98.09$ g/mol.
What is the molar mass of $\text{Al}_2(\text{SO}_4)_3$? (Al = 26.98, S = 32.07, O = 16.00)
$2(26.98) + 3(32.07) + 12(16.00) = 53.96 + 96.21 + 192.00 = 342.17$ g/mol. 150.05 forgets to multiply through the parentheses.
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