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

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

Question 1

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

Accepted Answer

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

Question 2

A compound has an empirical formula of $$\mathrm{CH_2O}$$ and a molar mass of $$180\ \mathrm{g/mol}. $$What is its molecular formula?

Accepted Answer

$$\mathrm{C_6H_{12}O_6$}$$

Question 3

Which of the following compounds has the same empirical and molecular formula?

Accepted Answer

Methane ($$\mathrm{CH_4$})$$

Question 4

A sample of a compound contains 4.1 g of C, 1.4 g of H, and 7.1 g of Cl. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{CH_2Cl}$$

Question 5

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

Accepted Answer

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

Question 6

A compound is found to contain 79.85% Cu and 20.15% S by mass. What is its empirical formula?

Accepted Answer

$$\mathrm{CuS}$$

Question 7

Which of the following steps is NOT part of determining an empirical formula from percent composition?

Accepted Answer

Multiply the mole ratios by the molar mass of the compound.

Question 8

A hydrocarbon is combusted and produces $$2.20\ \mathrm{g} of$$ $$\mathrm{CO_2$}$$ and $$0.90\ \mathrm{g} of$$ $$\mathrm{H_2O}. $$What is the empirical formula of the hydrocarbon?

Accepted Answer

$$\mathrm{CH_4$}$$

Question 9

If the empirical formula mass of a compound is $$58\ \mathrm{g/mol}$$ and its molar mass is $$174\ \mathrm{g/mol}$$, what is the molecular formula?

Accepted Answer

$$\mathrm{C_9H_{18}O_3$}$$

Question 10

Which of the following best explains why glucose ($$\mathrm{C_6H_{12}O_6$}) $$and formaldehyde ($$\mathrm{CH_2O}) $$have the same empirical formula but different molecular formulas?

Accepted Answer

Their simplest whole-number ratio of elements is the same, but the total number of atoms in each molecule is different.

Question 11

A sample of iron(III) oxide ($$\mathrm{Fe_2O_3}) $$has a mass of $$159.7\ \mathrm{g}. $$What is the percent by mass of iron in the compound? (Molar mass: Fe = $$55.85\ \mathrm{g/mol}$$, O = $$16.00\ \mathrm{g/mol})$$

Accepted Answer

$$69.94\%$$

Question 12

Which of the following is a correct step in determining the molecular formula from the empirical formula?

Accepted Answer

Divide the molar mass of the compound by the empirical formula mass.

Question 13

A compound contains 40.0% C, 6.7% H, and 53.3% O by mass. What is its empirical formula?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 14

Which of the following best describes the information provided by a mass spectrum in the context of molecular formula determination?

Accepted Answer

It provides the molar mass of the compound, which can be used to determine the molecular formula from the empirical formula.

Question 15

Which of the following is a correct statement about the relationship between empirical and molecular formulas?

Accepted Answer

The molecular formula is always a multiple of the empirical formula.

Question 16

A compound has a molar mass of $$90.0\ \mathrm{g/mol}$$ and an empirical formula of $$\mathrm{CH_2Cl}. $$What is its molecular formula?

Accepted Answer

$$\mathrm{C_3H_6Cl_3}$$

Question 17

Which of the following is NOT a correct empirical formula for the given molecular formula?

Accepted Answer

Empirical formula of $$\mathrm{C_4H_{10}} is$$ $$\mathrm{C_2H_5}$$

Empirical and Molecular Formulas: Concepts, Calculations, and Applications

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