Question 1

A compound contains 40.0 g of carbon, 6.7 g of hydrogen, and 53.3 g of oxygen. What is the empirical formula of this compound?

Accepted Answer

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

Question 2

A sample of a compound is found to contain 21.6% sodium, 33.3% chlorine, and 45.1% oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{NaClO}_3$$

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

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 of each element in a molecule.

Question 5

A compound is found to contain 70.0% iron and 30.0% oxygen by mass. What is the empirical formula of the compound? (Fe: 55.85 g/mol, O: 16.00 g/mol)

Accepted Answer

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

Question 6

A 10.0 g sample of a compound contains 2.24 g of nitrogen and 7.76 g of oxygen. What is the empirical formula of the compound? (N: 14.01 g/mol, O: 16.00 g/mol)

Accepted Answer

$$\mathrm{NO}_2$$

Question 7

A compound has a percent composition of 85.7% carbon and 14.3% hydrogen. What is the empirical formula of the compound?

Accepted Answer

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

Question 8

A compound has an empirical formula of $$\mathrm{C}_2\mathrm{H}_5$$ and a molar mass of 58 g/mol. What is its molecular formula?

Accepted Answer

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

Question 9

Which of the following steps is NOT required when determining the empirical formula from percent composition?

Accepted Answer

Add the atomic numbers of all elements together.

Question 10

A compound is found to have the empirical formula $$\mathrm{CH}$$ and a molar mass of 78 g/mol. What is the molecular formula?

Accepted Answer

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

Question 11

A chemist analyzes a new compound and finds it contains 24.3 g of magnesium and 10.7 g of nitrogen. What is the empirical formula? (Mg: 24.31 g/mol, N: 14.01 g/mol)

Accepted Answer

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

Question 12

A compound has a percent composition of 36.5% sodium, 25.4% sulfur, and 38.1% oxygen. What is the empirical formula?

Accepted Answer

$$\mathrm{Na}_2\mathrm{SO}_4$$

Question 13

A compound has an empirical formula of $$\mathrm{C}_2\mathrm{H}_3\mathrm{O}$$ and a molar mass of 86 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C}_4\mathrm{H}_6\mathrm{O}_2$$

Question 14

A 5.00 g sample of a compound contains 2.20 g of phosphorus and 2.80 g of oxygen. What is the empirical formula? (P: 30.97 g/mol, O: 16.00 g/mol)

Accepted Answer

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

Question 15

A compound is found to contain 63.5% silver, 8.2% nitrogen, and 28.3% oxygen. What is the empirical formula?

Accepted Answer

$$\mathrm{AgNO}_3$$

Question 16

A compound has an empirical formula of $$\mathrm{C}_3\mathrm{H}_7$$ and a molar mass of 86 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_{14}$$

Question 17

Which of the following is the correct sequence of steps to determine the empirical formula from mass data?

Accepted Answer

Convert mass to moles, divide by smallest number of moles, round to nearest whole number.

Empirical and Molecular Formulas: Calculation Methods

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