Compute the molar mass of ammonium sulfate, (NH4)2SO4.

• A. 132.14 g/mol
• B. 110.12 g/mol
• C. 144.16 g/mol
• D. 122.10 g/mol

Answer: (A)

Molar mass is the total mass of one mole of a compound, found by adding the atomic masses of every atom in its formula. For ammonium sulfate, the formula has two ammonium units and one sulfate unit. So combine two times the mass of NH4 with the mass of SO4: 2 × (N + 4H) + (S + 4O). Using standard atomic weights (N ≈ 14.01, H ≈ 1.01, S ≈ 32.07, O ≈ 16.00), that becomes 2 × (14.01 + 4×1.01) + (32.07 + 4×16.00) = 2 × (14.01 + 4.04) + (32.07 + 64.00) = 2 × 18.05 + 96.07 ≈ 36.10 + 96.07 ≈ 132.17 g/mol, which rounds to about 132.14 g/mol depending on rounding. Therefore the molar mass is about 132.14 g/mol.