Q: A sample of water is analyzed and found to contain 2.02 g of hydrogen and 16.00 g of oxygen. What is the percent by mass of hydrogen in water?

$\frac{2.02}{18.02} \times 100 = 11.2\%$

Q: Which of the following is the correct formula to calculate the percent composition by mass of an element in a compound?

$\frac{\text{mass of element in 1 mol of compound}}{\text{molar mass of compound}} \times 100\%$

Q: A compound is found to contain 0.25 mol of nitrogen and 1.00 mol of oxygen. What is the empirical formula?

$\mathrm{N}_1\mathrm{O}_4$ \text{ or } \mathrm{NO}_4$

Question 1

A sample of water is analyzed and found to contain 2.02 g of hydrogen and 16.00 g of oxygen. What is the percent by mass of hydrogen in water?

Accepted Answer

$\frac{2.02}{18.02} 	imes 100 = 11.2\%$

Question 2

A compound is found to be 64.82% carbon, 21.59% oxygen, and 13.59% hydrogen by mass. What is the empirical formula of this compound?

Accepted Answer

$\mathrm{C}_4\mathrm{H}_{10}\mathrm{O}$

Question 3

Which of the following best describes the difference between an empirical formula and a molecular formula?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms, while the molecular formula shows the actual number of atoms in a molecule.

Question 4

A compound has an empirical formula of $\mathrm{CH}_2\mathrm{O}$ and a molar mass of $180.0\ \mathrm{g/mol}$. What is its molecular formula?

Accepted Answer

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

Question 5

A nitrogen oxide contains 36.85% nitrogen by mass. What is the empirical formula of this compound?

Accepted Answer

$\mathrm{N}_2\mathrm{O}_3$

Question 6

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 7

A compound has the empirical formula $\mathrm{C}_4\mathrm{H}_{10}\mathrm{O}$ and a molar mass of $222.1\ \mathrm{g/mol}$. What is its molecular formula?

Accepted Answer

$\mathrm{C}_{12}\mathrm{H}_{30}\mathrm{O}_3$

Question 8

Which of the following is the correct formula to calculate the percent composition by mass of an element in a compound?

Accepted Answer

$\frac{	ext{mass of element in 1 mol of compound}}{	ext{molar mass of compound}} 	imes 100\%$

Question 9

A sample of a compound contains 1.056 g of Sn and 1.947 g of I. After the reaction, 0.601 g of Sn is recovered. What is the empirical formula of the compound formed?

Accepted Answer

$\mathrm{SnI}_4$

Question 10

Which of the following statements is true regarding the empirical formulas of $\mathrm{NO}_2$ and $\mathrm{N}_2\mathrm{O}_4$?

Accepted Answer

Both $\mathrm{NO}_2$ and $\mathrm{N}_2\mathrm{O}_4$ have the same empirical formula.

Question 11

A compound contains 27.3% carbon and 72.7% oxygen by mass. What is the empirical formula of this compound?

Accepted Answer

$\mathrm{CO}_2$

Question 12

A compound has an empirical formula of $\mathrm{CH}_2$ and a molar mass of $56.1\ \mathrm{g/mol}$. What is its molecular formula?

Accepted Answer

$\mathrm{C}_4\mathrm{H}_8$

Question 13

A compound is found to contain 0.20 mol of nitrogen and 0.50 mol of oxygen. What is the empirical formula?

Accepted Answer

$\mathrm{N}_2\mathrm{O}_5$

Question 14

A compound has a molar mass of $58.12\ \mathrm{g/mol}$ and an empirical formula of $\mathrm{C}_2\mathrm{H}_5$. What is its molecular formula?

Accepted Answer

$\mathrm{C}_4\mathrm{H}_{10}$

Question 15

A compound is found to contain 0.25 mol of nitrogen and 1.00 mol of oxygen. What is the empirical formula?

Accepted Answer

$\mathrm{N}_1\mathrm{O}_4$ 	ext{ or } \mathrm{NO}_4$

Question 16

A compound has a percent composition of 52.2% carbon, 13.0% hydrogen, and 34.8% oxygen. What is the empirical formula?

Accepted Answer

$\mathrm{C}_2\mathrm{H}_6\mathrm{O}$

Question 17

A compound has an empirical formula of $\mathrm{CH}_2\mathrm{O}$ and a molar mass of $90.0\ \mathrm{g/mol}$. What is its molecular formula?

Accepted Answer

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

Percent Composition, Empirical and Molecular Formulas in General Chemistry

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