Empirical formulas Knowledge-Based Practice

Questions

1. 1.

   Which of the following pairs of compounds have the same empirical formula?

   • A) $\text{C}_2\text{H}_6$ and $\text{C}_3\text{H}_6$
   • B) $\text{NO}_2$ and $\text{N}_2\text{O}_5$
   • C) $\text{C}_2\text{H}_2$ and $\text{C}_6\text{H}_6$
   • D) $\text{H}_2\text{O}$ and $\text{H}_2\text{O}_2$
2. 2.

   A 1.38 g sample of an unknown organic compound containing only carbon, hydrogen, and oxygen is burned completely in oxygen, yielding 2.64 g of $\text{CO}_2$ and 1.62 g of $\text{H}_2\text{O}$. What is the empirical formula of the compound? (Molar 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) $\text{C}_2\text{H}_4\text{O}$
   • C) $\text{C}_3\text{H}_8\text{O}$
   • D) $\text{C}_2\text{H}_6\text{O}$
3. 3.

   When a 4.86 g sample of magnesium metal is heated in pure nitrogen gas, it completely reacts to produce 6.73 g of a magnesium nitride compound. What is the empirical formula of this compound? (Molar masses: Mg = 24.3 g/mol, N = 14.0 g/mol)

   • A) $\text{MgN}$
   • B) $\text{Mg}_3\text{N}_2$
   • C) $\text{Mg}_2\text{N}_3$
   • D) $\text{MgN}_2$
4. 4.

   A compound consists of 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of this compound? (Molar masses: $\text{C} = 12.0\text{ g/mol}$, $\text{H} = 1.0\text{ g/mol}$, $\text{O} = 16.0\text{ g/mol}$)

   • A) $\text{CHO}$
   • B) $\text{CHO}_2$
   • C) $\text{CH}_2\text{O}$
   • D) $\text{C}_2\text{H}_5\text{O}$
5. 5.

   A sample of an iron oxide contains 69.9% iron and 30.1% oxygen by mass. What is the empirical formula of this compound? (Molar masses: $\text{Fe} = 55.8\text{ g/mol}$, $\text{O} = 16.0\text{ g/mol}$)

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

Answers and step-by-step solutions appear after you finish the test.