The mass of one mole of $(NH_{4})_{2}CO_{3}$ is   [O=16.0, N=14.0, C=12.0, H=1.0]

Analyze the question: We need the molar mass of ammonium carbonate, (NH₄)₂CO₃, which is the sum of the atomic masses of all atoms in one formula unit.

Concept: Molar mass = sum of (number of atoms × atomic mass). The subscript outside the bracket multiplies everything inside it.

Count the atoms in (NH₄)₂CO₃:

• N: 1 × 2 = 2
• H: 4 × 2 = 8
• C: 1
• O: 3

Calculate:

• N: 2 × 14.0 = 28.0
• H: 8 × 1.0 = 8.0
• C: 1 × 12.0 = 12.0
• O: 3 × 16.0 = 48.0

Total = 28.0 + 8.0 + 12.0 + 48.0 = 96.0 g/mol

So one mole of (NH₄)₂CO₃ has a mass of **96.

Why the other options are wrong:

• 66.0 g would come from mistakenly leaving out the H or N multiplication.
• 76.0 g and 80.0 g come from miscounting the atoms inside the bracket.

Exam tip: When you see a bracket with a subscript, multiply every atom inside by that number first. Then list N, H, C and O separately and add them. Writing out the atom counts helps you avoid slips.