Percent composition Knowledge-Based Practice

Chemistry · The Mole & Stoichiometry · Chemistry · The Mole

5 Chemistry practice questions on Percent composition. Questions that assess core concepts and understanding.

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Questions

1.
What mass of iron is contained in a 250.0 g sample of pure iron(III) oxide, $\text{Fe}_2\text{O}_3$ ? (Molar masses: $\text{Fe} = 55.85\text{ g/mol}$ , $\text{O} = 16.00\text{ g/mol}$ )
- A) 75.1 g
- B) 87.4 g
- C) 194.3 g
- D) 174.9 g
2.
What is the percent by mass of water in copper(II) sulfate pentahydrate, $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$ ? (Molar masses: $\text{Cu} = 63.55\text{ g/mol}$ , $\text{S} = 32.06\text{ g/mol}$ , $\text{O} = 16.00\text{ g/mol}$ , $\text{H} = 1.01\text{ g/mol}$ )
- A) 25.45%
- B) 36.08%
- C) 56.45%
- D) 63.92%
3.
A 15.00 g sample of a pure compound containing only calcium and chlorine is decomposed into its constituent elements, yielding 5.42 g of calcium. What is the percent by mass of chlorine in this compound?
- A) 63.9%
- B) 36.1%
- C) 56.6%
- D) 54.2%
4.
What is the percent by mass of oxygen in magnesium hydroxide, $\text{Mg(OH)}_2$ ? (Molar masses: $\text{Mg} = 24.31\text{ g/mol}$ , $\text{O} = 16.00\text{ g/mol}$ , $\text{H} = 1.01\text{ g/mol}$ )
- A) 27.4%
- B) 54.9%
- C) 41.7%
- D) 34.6%
5.
What is the percent by mass of nitrogen in ammonium nitrate, $\text{NH}_4\text{NO}_3$ ? (Molar masses: $\text{N} = 14.0\text{ g/mol}$ , $\text{H} = 1.0\text{ g/mol}$ , $\text{O} = 16.0\text{ g/mol}$ )
- A) 35.0%
- B) 17.5%
- C) 28.0%
- D) 60.0%

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