Molecular formulas Original Scenario-Based Download PDF

Questions

1. 1.

   In an orbital habitat's life-support testing facility, engineers evaluate an unidentified synthetic hydrocarbon fuel recovered from an auxiliary thruster. Complete combustion of a 0.250-mol sample of this pure fuel in excess oxygen yields 33.0 g of carbon dioxide ($\text{CO}_2$) and 18.0 g of water ($\text{H}_2\text{O}$). What is the molecular formula of this hydrocarbon? (Molar masses: $\text{CO}_2 = 44.0\text{ g/mol}$, $\text{H}_2\text{O} = 18.0\text{ g/mol}$)

   • A) $\text{C}_3\text{H}_4$
   • B) $\text{C}_2\text{H}_6$
   • C) $\text{C}_3\text{H}_8$
   • D) $\text{C}_4\text{H}_{10}$
2. 2.

   During an atmospheric survey of a distant moon, a robotic probe collects a sample of a dense refrigerant gas escaping from cryovolcanic vents. Elemental analysis shows that the gas has the empirical formula $\text{CF}_2$. At standard temperature and pressure (STP), a $5.60\text{ L}$ sample of this pure vapor has a mass of $50.0\text{ g}$. Given that the molar volume of an ideal gas at STP is $22.4\text{ L/mol}$, what is the molecular formula of this compound? (Atomic masses: $\text{C} = 12.0\text{ g/mol}$, $\text{F} = 19.0\text{ g/mol}$)

   • A) $\text{C}_4\text{F}_8$
   • B) $\text{C}_2\text{F}_4$
   • C) $\text{C}_3\text{F}_6$
   • D) $\text{C}_5\text{F}_{10}$
3. 3.

   In an orbital biosphere simulator, life-support engineers detect an unknown volatile pheromone released by a genetically engineered flora. Complete elemental breakdown of a 0.050-mol sample of this pure organic compound yields 4.80 g of carbon, 0.50 g of hydrogen, and 3.20 g of oxygen. Given atomic masses of 12.0 g/mol for C, 1.0 g/mol for H, and 16.0 g/mol for O, what is the molecular formula of this pheromone?

   • A) $\text{C}_4\text{H}_5\text{O}_2$
   • B) $\text{C}_6\text{H}_8\text{O}_3$
   • C) $\text{C}_8\text{H}_{10}\text{O}_4$
   • D) $\text{C}_{12}\text{H}_{15}\text{O}_6$
4. 4.

   A deep-sea research submersible collects an iridescent secretion produced by an unknown species of abyssal siphonophore. Chemical analysis reveals that the compound is composed of 54.53% carbon, 9.15% hydrogen, and 36.32% oxygen by mass, with an experimentally measured molar mass of $88.11\text{ g/mol}$. Given atomic masses of $\text{C} = 12.01\text{ g/mol}$, $\text{H} = 1.008\text{ g/mol}$, and $\text{O} = 16.00\text{ g/mol}$, what is the molecular formula of this substance?

   • A) $\text{C}_4\text{H}_8\text{O}_2$
   • B) $\text{C}_2\text{H}_4\text{O}$
   • C) $\text{C}_3\text{H}_4\text{O}_3$
   • D) $\text{C}_5\text{H}_{12}\text{O}$
5. 5.

   A xenobiologist exploring an icy moon isolates a volatile defensive compound produced by an extremophile colony. Elemental analysis reveals that the compound has an empirical formula of $\text{C}_3\text{H}_5\text{N}$, and mass spectrometry measures its molar mass to be $220.36\text{ g/mol}$. Given atomic masses of $\text{C} = 12.01\text{ g/mol}$, $\text{H} = 1.01\text{ g/mol}$, and $\text{N} = 14.01\text{ g/mol}$, what is the molecular formula of this compound?

   • A) $\text{C}_6\text{H}_{10}\text{N}_2$
   • B) $\text{C}_{12}\text{H}_{20}\text{N}_4$
   • C) $\text{C}_9\text{H}_{15}\text{N}_3$
   • D) $\text{C}_{15}\text{H}_{25}\text{N}_5$