Let’s solve each problem step by step. We’ll find the molar mass of each compound by adding up the atomic masses of all the atoms in the formula.
We’ll use these approximate atomic masses (from the periodic table):
- Na = 23.0 g/mol
- Br = 79.9 g/mol
- Pb = 207.2 g/mol
- S = 32.1 g/mol
- O = 16.0 g/mol
- Ca = 40.1 g/mol
- H = 1.0 g/mol
- P = 31.0 g/mol
- N = 14.0 g/mol
- C = 12.0 g/mol
- Fe = 55.8 g/mol
- Zn = 65.4 g/mol
- Ag = 107.9 g/mol
- F = 19.0 g/mol
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1) NaBr
Na: 1 × 23.0 = 23.0
Br: 1 × 79.9 = 79.9
Total = 23.0 + 79.9 =
102.9 g/mol
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2) PbSO₄
Pb: 1 × 207.2 = 207.2
S: 1 × 32.1 = 32.1
O: 4 × 16.0 = 64.0
Total = 207.2 + 32.1 + 64.0 =
303.3 g/mol
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3) Ca(OH)₂
Ca: 1 × 40.1 = 40.1
O: 2 × 16.0 = 32.0 (because OH is multiplied by 2 → 2 O atoms)
H: 2 × 1.0 = 2.0 (same reason → 2 H atoms)
Total = 40.1 + 32.0 + 2.0 =
74.1 g/mol
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4) Na₃PO₄
Na: 3 × 23.0 = 69.0
P: 1 × 31.0 = 31.0
O: 4 × 16.0 = 64.0
Total = 69.0 + 31.0 + 64.0 =
164.0 g/mol
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5) (NH₄)₂CO₃
First, break it down:
(NH₄)₂ means 2 NH₄ groups → so 2 N and 8 H
CO₃ means 1 C and 3 O
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
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6) C₆H₁₂O₆
C: 6 × 12.0 = 72.0
H: 12 × 1.0 = 12.0
O: 6 × 16.0 = 96.0
Total = 72.0 + 12.0 + 96.0 =
180.0 g/mol
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7) Fe₃(PO₄)₂
Fe: 3 × 55.8 = 167.4
P: 2 × 31.0 = 62.0 (because PO₄ is multiplied by 2 → 2 P atoms)
O: 8 × 16.0 = 128.0 (each PO₄ has 4 O → 2×4=8 O atoms)
Total = 167.4 + 62.0 + 128.0 =
357.4 g/mol
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8) (NH₄)₂S
(NH₄)₂ → 2 N and 8 H
S → 1 S
N: 2 × 14.0 = 28.0
H: 8 × 1.0 = 8.0
S: 1 × 32.1 = 32.1
Total = 28.0 + 8.0 + 32.1 =
68.1 g/mol
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9) Zn(C₂H₃O₂)₂
Zn: 1 × 65.4 = 65.4
Inside parentheses: C₂H₃O₂ — but multiplied by 2 → so double everything inside
C: 2 × 2 = 4 atoms → 4 × 12.0 = 48.0
H: 3 × 2 = 6 atoms → 6 × 1.0 = 6.0
O: 2 × 2 = 4 atoms → 4 × 16.0 = 64.0
Plus Zn: 65.4
Total = 65.4 + 48.0 + 6.0 + 64.0 =
183.4 g/mol
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10) AgF
Ag: 1 × 107.9 = 107.9
F: 1 × 19.0 = 19.0
Total = 107.9 + 19.0 =
126.9 g/mol
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Final Answer:
1) 102.9 g/mol
2) 303.3 g/mol
3) 74.1 g/mol
4) 164.0 g/mol
5) 96.0 g/mol
6) 180.0 g/mol
7) 357.4 g/mol
8) 68.1 g/mol
9) 183.4 g/mol
10) 126.9 g/mol
Parent Tip: Review the logic above to help your child master the concept of formula mass worksheet.
