Empirical formulas Original Scenario-Based Download PDF

Questions

1. 1.

   Inside an atmospheric forge aboard a skyward research vessel, an alchemical technician burns a 1.239 g sample of pure elemental phosphorus in an enclosed oxygen chamber to synthesize an insulating ceramic powder known as "frost-fire ash". The complete oxidation yields 2.839 g of the purified oxide compound. Given the molar masses of phosphorus (30.97 g/mol) and oxygen (16.00 g/mol), what is the empirical formula of frost-fire ash?

   • A) $PO_2$
   • B) $PO_3$
   • C) $P_2O_5$
   • D) $P_5O_2$
2. 2.

   Deep inside an ancient dwarven observatory, arcanists discover an enchanted liquid propellant called "pyro-dew" composed entirely of carbon, hydrogen, and oxygen. Complete combustion of a 1.38 g sample of this substance in excess oxygen yields 2.64 g of carbon dioxide ($CO_2$) and 1.62 g of water ($H_2O$). Using molar masses of 12.0 g/mol for C, 1.0 g/mol for H, and 16.0 g/mol for O, what is the empirical formula of pyro-dew?

   • A) $C_2H_6O$
   • B) $CH_3O$
   • C) $CH_2O$
   • D) $C_3H_8O$
3. 3.

   Xenobiologists exploring a subterranean biome isolate a volatile alkaloid known as "glimmer-sap" secreted by bioluminescent cave moss. Quantitative elemental analysis reveals that the purified compound consists of 60.96% carbon, 15.35% hydrogen, and 23.69% nitrogen by mass. Given the molar masses of carbon (12.01 g/mol), hydrogen (1.01 g/mol), and nitrogen (14.01 g/mol), what is the empirical formula of glimmer-sap?

   • A) $C_3H_9N$
   • B) $C_2H_6N$
   • C) $C_3H_7N$
   • D) $C_4H_{11}N$
4. 4.

   Aboard an orbital habitat, technicians harvest a flexible synthetic polymer dubbed "star-resin" designed to mend microscopic hull breaches. Elemental analysis reveals that a 4.40 g sample of this purified resin consists of 2.40 g of carbon, 0.40 g of hydrogen, and 1.60 g of oxygen. Given the molar masses of carbon (12.0 g/mol), hydrogen (1.0 g/mol), and oxygen (16.0 g/mol), what is the empirical formula of the compound?

   • A) $\text{CH}_2\text{O}$
   • B) $\text{C}_2\text{H}_4\text{O}$
   • C) $\text{C}_4\text{H}_8\text{O}_2$
   • D) $\text{C}_6\text{H}\text{O}_4$
5. 5.

   During an expedition to an uncharted subterranean cavern, planetary geologists recover a luminescent mineral dust labeled "solar rust." Quantitative analysis of a 10.00 g sample of this purified substance reveals that it contains 6.99 g of iron and 3.01 g of oxygen. Given the molar masses of iron (55.85 g/mol) and oxygen (16.00 g/mol), what is the empirical formula of this compound?

   • A) $\mathrm{Fe}_{2}\mathrm{O}_{3}$
   • B) $\mathrm{FeO}$
   • C) $\mathrm{Fe}_{3}\mathrm{O}_{4}$
   • D) $\mathrm{FeO}_{2}$