Molecular formulas Transitional Reasoning Download PDF

Questions

1. 1.

   An analytical chemist investigating an industrial sulfur pollutant determines that its empirical formula is $\text{CH}_3\text{S}$. Complete combustion of a 0.200 mol sample of this pure compound in excess oxygen produces 17.6 g of carbon dioxide gas ($\text{CO}_2$) alongside sulfur dioxide and water vapor. What is the molecular formula of this pollutant? (Atomic masses: $\text{C} = 12.0\text{ g/mol}$, $\text{H} = 1.0\text{ g/mol}$, $\text{O} = 16.0\text{ g/mol}$, $\text{S} = 32.1\text{ g/mol}$)

   • A) $\text{CH}_3\text{S}$
   • B) $\text{C}_2\text{H}_6\text{S}_2$
   • C) $\text{C}_3\text{H}_9\text{S}_3$
   • D) $\text{C}_4\text{H}_{12}\text{S}_4$
2. 2.

   Complete combustion of a 0.450 g sample of an unknown organic compound containing only carbon, hydrogen, and oxygen produces 0.660 g of carbon dioxide and 0.270 g of water. In a separate experiment, mass spectrometry determines that the molar mass of the compound is 90.0 g/mol. What is the molecular formula of this compound? (Atomic masses: $\text{C} = 12.0\text{ g/mol}$, $\text{H} = 1.0\text{ g/mol}$, $\text{O} = 16.0\text{ g/mol}$)

   • A) $\text{CH}_2\text{O}$
   • B) $\text{C}_2\text{H}_4\text{O}_2$
   • C) $\text{C}_6\text{H}_{12}\text{O}_6$
   • D) $\text{C}_3\text{H}_6\text{O}_3$
3. 3.

   A synthetic chemist analyzes a solid oxide of phosphorus produced by burning pure phosphorus in dry air. Elemental analysis shows that the oxide consists of 43.6% phosphorus and 56.4% oxygen by mass. In a separate measurement, a sample containing $1.505 \times 10^{22}$ molecules of this compound has a mass of 7.10 g. What is the molecular formula of the oxide? (Atomic masses: $\text{P} = 31.0\text{ g/mol}$, $\text{O} = 16.0\text{ g/mol}$; Avogadro's number: $N_A = 6.02 \times 10^{23}\text{ mol}^{-1}$)

   • A) $\text{P}_4\text{O}_{10}$
   • B) $\text{P}_2\text{O}_5$
   • C) $\text{P}_4\text{O}_6$
   • D) $\text{P}_2\text{O}_3$
4. 4.

   An industrial chemist analyzes an unknown gaseous hydrocarbon emitted during polymer manufacturing and finds it consists of 85.6% carbon and 14.4% hydrogen by mass. In a separate physical measurement at standard temperature and pressure (STP), a 5.60 L sample of this pure gas has a mass of 14.0 g. What is the molecular formula of this hydrocarbon? (Molar masses: C = 12.0 g/mol, H = 1.0 g/mol; molar volume of gas at STP = 22.4 L/mol)

   • A) $\text{C}_3\text{H}_6$
   • B) $\text{C}_4\text{H}_8$
   • C) $\text{C}_5\text{H}_{10}$
   • D) $\text{C}_6\text{H}_{12}$
5. 5.

   A chemist analyzes an unknown liquid used as an industrial flavoring agent and determines that its empirical formula is $\text{C}_2\text{H}_4\text{O}$. In a subsequent vapor analysis, a 0.250 mol sample of the pure compound is found to have a mass of 22.0 g. What is the molecular formula of this compound? (Atomic masses: C = 12.0 g/mol, H = 1.0 g/mol, O = 16.0 g/mol)

   • A) $\text{C}_2\text{H}_4\text{O}$
   • B) $\text{C}_3\text{H}_6\text{O}_2$
   • C) $\text{C}_4\text{H}_8\text{O}_2$
   • D) $\text{C}_6\text{H}_{12}\text{O}_3$