Empirical formulas Transitional Reasoning Download PDF

Questions

1. 1.

   To identify an iron oxide present in a mineral sample, an analyst heats a 3.48 g sample of the oxide in a tube furnace under a steady stream of dry hydrogen gas until it is completely reduced to 2.52 g of pure iron metal. Assuming all oxygen is removed as water vapor and using molar masses of $\text{Fe} = 56.0\text{ g/mol}$ and $\text{O} = 16.0\text{ g/mol}$, what is the empirical formula of this iron oxide?

   • A) $\text{FeO}$
   • B) $\text{Fe}_2\text{O}_3$
   • C) $\text{Fe}_3\text{O}_2$
   • D) $\text{Fe}_3\text{O}_4$
2. 2.

   A chemistry student investigates the thermal decomposition of a pure solid salt containing potassium, chlorine, and oxygen. Heating a 2.45 g sample strongly drives off all the oxygen as gas, leaving behind 1.49 g of solid potassium chloride ($KCl$). Given the molar masses of $K = 39.1\text{ g/mol}$, $Cl = 35.5\text{ g/mol}$, and $O = 16.0\text{ g/mol}$, what is the empirical formula of the original salt?

   • A) $KClO_3$
   • B) $KClO_4$
   • C) $KClO_2$
   • D) $KClO$
3. 3.

   Industrial catalysts used in the Contact process to manufacture sulfuric acid rely on an active vanadium oxide compound. Quantitative elemental analysis indicates that this oxide contains 56.0% vanadium and 44.0% oxygen by mass. Given that the molar mass of vanadium is 51.0 g/mol and that of oxygen is 16.0 g/mol, which of the following is the empirical formula of the compound?

   • A) $VO$
   • B) $VO_2$
   • C) $V_2O_3$
   • D) $V_2O_5$
4. 4.

   In an investigation to determine the empirical formula of an oxide of phosphorus, a student completely reacts a 4.34 g sample of pure phosphorus with excess oxygen gas. The reaction yields 9.94 g of a single solid phosphorus oxide product. Given the molar masses of phosphorus (31.0 g/mol) and oxygen (16.0 g/mol), what is the empirical formula of this compound?

   • A) $PO_3$
   • B) $P_2O_5$
   • C) $P_2O_3$
   • D) $PO_2$
5. 5.

   A 4.60 g sample of a liquid fuel containing only carbon, hydrogen, and oxygen undergoes complete combustion, yielding 8.80 g of $CO_2$ and 5.40 g of $H_2O$. Using molar masses of 12.0 g/mol for carbon, 1.0 g/mol for hydrogen, and 16.0 g/mol for oxygen, which empirical formula represents this compound?

   • A) $C_2H_3O$
   • B) $C_2H_6O$
   • C) $C_2H_4O$
   • D) $C_3H_8O_2$