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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