Q: A weather balloon contains 44.0 L of helium at a certain temperature and pressure. If the amount of helium is increased from 2.0 moles to 5.0 moles, what is the new volume, assuming temperature and pressure remain constant?

$$V_2$$ = $$V_1$$ \times \frac{$$n_2$$}{$$n_1$$} = 44.0 \times \frac{5.0}{2.0} = 110\ \text{L}$$

Q: At STP, what is the volume occupied by 4.00 g of methane ($$CH_4$$)? (Molar mass of $$CH_4 = 16.05$$\ \text{g/mol}$$)

$$\text{Moles of } CH_4$ = \frac{4.00}{16.05} = 0.249\ \text{mol};\ V = 0.249 \times 22.4 = 5.58\ \text{L}$$

Q: A scuba diver uses a gas mixture with a total pressure of 8.00 atm. If the partial pressure of oxygen is 1280 mmHg, what is the partial pressure of helium in atm? (1 atm = 760 mmHg)

$$P_{\text{He}} = 8.00\ \text{atm} - \frac{1280}{760}\ \text{atm} = 6.32\ \text{atm}$$

Q: Which of the following is the correct molar mass of $$C_2H_6O ($$ethanol)? (C: 12.01 g/mol, H: 1.01 g/mol, O: 16.00 g/mol)

$$2 \times 12.01 + 6 \times 1.01 + 1 \times 16.00 = 46.08\ \text{g/mol}$$

Q: A 0.500 L sample of gas at 1.00 atm and 273 K contains how many moles of gas?

$$n = \frac{V}{22.4} = \frac{0.500}{22.4} = 0.0223\ \text{mol}$$

Q: A 3.00 L container holds a mixture of three gases: $$O_2 at 0.50 $$atm, $$N_2 at 0.75 $$atm, and $$CO_2 at 0.25 $$atm. What is the total pressure in the container?

$$P_{\text{total}} = 0.50 + 0.75 + 0.25 = 1.50\ \text{atm}$$

Q: If 1.00 mole of $$SO_2$$ gas occupies 22.4 L at STP, what volume will 3.00 moles of $$SO_2$$ occupy at STP?

$$V = 3.00 \times 22.4 = 67.2\ \text{L}$$

Question 1

A sample of nitrogen gas has a volume of 2.50 L at a pressure of 1.20 atm and a temperature of 300 K. What will the volume be if the pressure is increased to 2.40 atm and the temperature is decreased to 250 K (assume the amount of gas remains constant)? Use the Combined Gas Law.

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$P_2$$} = \frac{1.20 	imes 2.50 	imes 250}{300 	imes 2.40} = 0.42\ 	ext{L}$$

Question 2

A weather balloon contains 44.0 L of helium at a certain temperature and pressure. If the amount of helium is increased from 2.0 moles to 5.0 moles, what is the new volume, assuming temperature and pressure remain constant?

Accepted Answer

$$V_2$$ = $$V_1$$ 	imes \frac{$$n_2$$}{$$n_1$$} = 44.0 	imes \frac{5.0}{2.0} = 110\ 	ext{L}$$

Question 3

Which of the following statements best describes Avogadro’s Law?

Accepted Answer

The volume of a gas is directly proportional to the number of moles of gas, provided temperature and pressure are constant.

Question 4

At STP, what is the volume occupied by 4.00 g of methane ($$CH_4$$)? (Molar mass of $$CH_4 = 16.05$$\ 	ext{g/mol}$$)

Accepted Answer

$$	ext{Moles of } CH_4$ = \frac{4.00}{16.05} = 0.249\ 	ext{mol};\ V = 0.249 	imes 22.4 = 5.58\ 	ext{L}$$

Question 5

A scuba diver uses a gas mixture with a total pressure of 8.00 atm. If the partial pressure of oxygen is 1280 mmHg, what is the partial pressure of helium in atm? (1 atm = 760 mmHg)

Accepted Answer

$$P_{	ext{He}} = 8.00\ 	ext{atm} - \frac{1280}{760}\ 	ext{atm} = 6.32\ 	ext{atm}$$

Question 6

Which of the following is the correct molar mass of $$C_2H_6O ($$ethanol)? (C: 12.01 g/mol, H: 1.01 g/mol, O: 16.00 g/mol)

Accepted Answer

$$2 	imes 12.01 + 6 	imes 1.01 + 1 	imes 16.00 = 46.08\ 	ext{g/mol}$$

Question 7

A 0.500 L sample of gas at 1.00 atm and 273 K contains how many moles of gas?

Accepted Answer

$$n = \frac{V}{22.4} = \frac{0.500}{22.4} = 0.0223\ 	ext{mol}$$

Question 8

Which of the following best describes Dalton’s Law of Partial Pressures?

Accepted Answer

The total pressure of a mixture of gases is equal to the sum of the partial pressures of each individual gas.

Question 9

A 3.00 L container holds a mixture of three gases: $$O_2 at 0.50 $$atm, $$N_2 at 0.75 $$atm, and $$CO_2 at 0.25 $$atm. What is the total pressure in the container?

Accepted Answer

$$P_{	ext{total}} = 0.50 + 0.75 + 0.25 = 1.50\ 	ext{atm}$$

Question 10

If 1.00 mole of $$SO_2$$ gas occupies 22.4 L at STP, what volume will 3.00 moles of $$SO_2$$ occupy at STP?

Accepted Answer

$$V = 3.00 	imes 22.4 = 67.2\ 	ext{L}$$

Question 11

A gas sample has a pressure of 2.00 atm, a volume of 1.50 L, and a temperature of 300 K. If the temperature is increased to 400 K and the pressure is decreased to 1.00 atm, what is the new volume?

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$P_2$$} = \frac{2.00 	imes 1.50 	imes 400}{300 	imes 1.00} = 4.00\ 	ext{L}$$

Question 12

Which of the following is NOT a correct statement about STP?

Accepted Answer

At STP, 1 mole of any gas occupies 1.00 L.

Question 13

A 0.250 mol sample of $$O_2$$ gas is collected at STP. What is its volume?

Accepted Answer

$$V = 0.250 	imes 22.4 = 5.60\ 	ext{L}$$

Question 14

Which of the following is the correct sequence of steps to calculate the molar mass of a compound?

Accepted Answer

Obtain the molar mass of each element, multiply by the number of atoms, then sum the results.

Question 15

A gas mixture contains 2.0 moles of $$N_2$$, 1.0 mole of $$O_2$$, and 1.0 mole of $$CO_2. If $$the total pressure is 4.0 atm, what is the partial pressure of $$N_2$$?

Accepted Answer

$$P_{N_2$} = \frac{2.0}{4.0} 	imes 4.0 = 2.0\ 	ext{atm}$$

Question 16

A 1.00 L sample of gas at 2.00 atm and 300 K is allowed to expand to 2.00 L and 400 K. What is the final pressure?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$V_2$$} = \frac{2.00 	imes 1.00 	imes 400}{300 	imes 2.00} = 1.33\ 	ext{atm}$$

Gas Laws, Molar Mass, and Dalton’s Law: Study Notes for GOB Chemistry

Study Guide - Practice Questions

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