How many moles of hydrogen atoms are present in 34.2 g of sucrose, C12H22O11? (Molar masses: C = 12.0 g/mol, H = 1.0 g/mol, O = 16.0 g/mol)
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Correct answer
C. 2.2 mol
Principle or equation
The amount of substance is mass divided by molar mass. Each formula unit of sucrose contains 22 hydrogen atoms, so moles of H atoms = moles of sucrose × 22.
Why this answer is correct
Molar mass of sucrose = 12×12 + 22×1 + 11×16 = 144 + 22 + 176 = 342 g/mol. Moles of sucrose = 34.2 g / 342 g/mol = 0.100 mol. Moles of H atoms = 0.100 mol × 22 = 2.20 mol.
Example
For H2O (molar mass 18 g/mol), 18 g contains 2 mol H atoms.
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