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

$$\text{Number of particles} = n \times N_A$$

Question 1

Which of the following best describes the empirical formula for glucose ($$C_6H_{12}O_6$)?

Accepted Answer

$$CH_2O$$

Question 2

If you have 32 g of $$CuO$$ and the molar mass of $$CuO is 80 g/$$mol, how many moles of $$CuO do $$you have?

Accepted Answer

$$0.40$$ mol

Question 3

What is the percentage by mass of oxygen in $$CuO$$? (Molar mass of $$CuO = 80 g/$$mol, mass of O = 16 g/mol)

Accepted Answer

$$40	ext{%}$$

Question 4

Given the formula $$C_6H_{12}O_6$, what is the molecular formula mass?

Accepted Answer

$$180 g/$$mol

Question 5

Which equation correctly relates the number of moles ($$n$$), mass ($$m$$), and molar mass ($$M$$)?

Accepted Answer

$$n = \frac{m}{M}$$

Question 6

How many molecules are present in 2 moles of $$H_2O$$? (Use $$N_A = 6.02 	imes 10$$^{23}$$)

Accepted Answer

$$1.20 	imes 10$$^{24}$$

Question 7

A compound contains 40.1% oxygen by mass. If the total mass of the compound is 156 g, what is the mass of oxygen present?

Accepted Answer

$$62.6 g$$

Question 8

Which of the following is the correct formula for calculating percent composition by mass?

Accepted Answer

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

Question 9

If a sample contains $$1.25$$ moles of $$O_2$$, how many molecules of $$O_2$$ are present?

Accepted Answer

$$7.53 	imes 10$$^{23}$$

Question 10

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

Accepted Answer

$$C_6H_{12}O_6$

Question 11

Which of the following best describes Avogadro's number?

Accepted Answer

The number of atoms in one mole of a substance

Question 12

If you have 64 g of $$O_2 ($$molar mass = 32 g/mol), how many moles of $$O_2 do $$you have?

Accepted Answer

$$2$$ mol

Question 13

Which of the following is NOT a step in determining the empirical formula from percent composition?

Accepted Answer

Multiply each percent by Avogadro's number

Question 14

A sample contains 20% sulfur by mass. If the total mass is 156 g, what is the mass of sulfur?

Accepted Answer

$$31.2 g$$

Question 15

Which of the following is the correct relationship for calculating the number of particles in a given number of moles?

Accepted Answer

$$	ext{Number of particles} = n 	imes N_A$$

Question 16

If the empirical formula of a compound is $$CH_2O$$ and its molar mass is 90 g/mol, what is the molecular formula?

Accepted Answer

$$C_3H_6O_3$$

Question 17

What is the mass percent of carbon in glucose ($$C_6H_{12}O_6$)? (Atomic masses: C = 12, H = 1, O = 16)

Accepted Answer

$$40	ext{%}$$

Question 18

Which of the following is the correct formula for calculating the mass of a substance from moles and molar mass?

Accepted Answer

$$m = n 	imes M$$

Empirical and Molecular Formulas, Percent Composition, and Moles in General Chemistry

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