Question 1

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of this compound?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 2

A 25.0 g sample of a compound contains 10.0 g of carbon, 1.67 g of hydrogen, and 13.3 g of oxygen. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 3

A compound has an empirical formula of $$\mathrm{CH}_2\mathrm{O}$$ and a molar mass of 180 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$$

Question 4

A 0.250 mol sample of nitrogen gas reacts with excess hydrogen gas to form ammonia according to the equation: $$\mathrm{N}_2 + 3\mathrm{H}_2 \rightarrow 2\mathrm{NH}_3. $$How many moles of ammonia are produced?

Accepted Answer

$$0.500$$ mol

Question 5

If 0.500 mol of magnesium reacts with 0.500 mol of oxygen gas to form magnesium oxide, what is the limiting reactant and how many moles of $$\mathrm{MgO}$$ are formed? (Reaction: $$2\mathrm{Mg} + \mathrm{O}_2 \rightarrow 2\mathrm{MgO})$$

Accepted Answer

Magnesium is limiting; $$0.500$$ mol $$\mathrm{MgO}$$ formed

Question 6

A student combusts 0.100 mol of glucose ($$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6) in $$excess oxygen. How many moles of $$\mathrm{CO}_2$$ are produced? (Reaction: $$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2 \rightarrow 6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O})$$

Accepted Answer

$$0.600$$ mol

Question 7

A sample of a compound contains 77.8% carbon and 22.2% hydrogen by mass. What is the empirical formula?

Accepted Answer

$$\mathrm{CH}_3$$

Question 8

A compound is found to have the empirical formula $$\mathrm{CH}_2\mathrm{O}$$ and a molar mass of 90 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C}_3\mathrm{H}_6\mathrm{O}_3$$

Question 9

A 0.250 mol sample of $$\mathrm{N}_2$$ reacts with 0.750 mol of $$\mathrm{H}_2 to $$form ammonia. What is the limiting reactant and how many moles of $$\mathrm{NH}_3$$ are produced? (Reaction: $$\mathrm{N}_2 + 3\mathrm{H}_2 \rightarrow 2\mathrm{NH}_3)$$

Accepted Answer

$$\mathrm{N}_2 is $$limiting; $$0.500$$ mol $$\mathrm{NH}_3$$ formed

Question 10

A compound is analyzed and found to contain 62.1% carbon, 10.4% hydrogen, and 27.5% oxygen by mass. What is the empirical formula?

Accepted Answer

$$\mathrm{C}_3\mathrm{H}_7\mathrm{O}$$

Question 11

A 0.500 mol sample of $$\mathrm{Mg}$$ reacts with 0.250 mol of $$\mathrm{O}_2 to $$form $$\mathrm{MgO}. $$What is the limiting reactant and how many moles of $$\mathrm{MgO}$$ are formed? (Reaction: $$2\mathrm{Mg} + \mathrm{O}_2 \rightarrow 2\mathrm{MgO})$$

Accepted Answer

$$\mathrm{Mg} is $$limiting; $$0.500$$ mol $$\mathrm{MgO}$$ formed

Question 12

A compound has a molar mass of 60.0 g/mol and an empirical formula of $$\mathrm{CH}_2\mathrm{O}. $$What is its molecular formula?

Accepted Answer

$$\mathrm{C}_2\mathrm{H}_4\mathrm{O}_2$$

Question 13

A 0.100 mol sample of $$\mathrm{C}_2\mathrm{H}_6 is $$combusted in excess oxygen. How many moles of $$\mathrm{CO}_2$$ are produced? (Reaction: $$2\mathrm{C}_2\mathrm{H}_6 + 7\mathrm{O}_2 \rightarrow 4\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O})$$

Accepted Answer

$$0.200$$ mol

Question 14

A compound is found to contain 85.7% carbon and 14.3% hydrogen by mass. What is the empirical formula?

Accepted Answer

$$\mathrm{CH}_2$$

Question 15

A 0.200 mol sample of $$\mathrm{C}_3\mathrm{H}_8 is $$combusted in excess oxygen. How many moles of $$\mathrm{CO}_2$$ are produced? (Reaction: $$\mathrm{C}_3\mathrm{H}_8 + 5\mathrm{O}_2 \rightarrow 3\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O})$$

Accepted Answer

$$0.600$$ mol

Empirical and Molecular Formulas: Calculations and Concepts

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