Question 1

A sample of air contains 78% nitrogen, 21% oxygen, 0.9% argon, and 0.04% carbon dioxide by volume. If the total pressure of the air is $$1.00\ \mathrm{atm}$$, what is the partial pressure of oxygen in the sample?

Accepted Answer

$$0.21\ \mathrm{atm}$$

Question 2

A mixture of three gases (Ar, Ne, and CO$$_2) $$has a total pressure of $$1.2\ \mathrm{atm}. If $$the mixture contains $$25.0\ \mathrm{g} of $$each gas, what is the partial pressure of Ne? (Molar masses: Ar = $$39.95\ \mathrm{g\ $$mol^{-1}$$}$$, Ne = $$20.18\ \mathrm{g\ $$mol^{-1}$$}$$, CO$$_2$$ = $$44.01\ \mathrm{g\ $$mol^{-1}$$})$$

Accepted Answer

$$0.61\ \mathrm{atm}$$

Question 3

According to Dalton’s Law of Partial Pressures, which of the following equations correctly expresses the total pressure of a mixture of unreactive gases?

Accepted Answer

$$P_{\mathrm{total}} = P_1$ + P_2$ + P_3$ + \cdots + P_n$$

Question 4

A $$5.0\ \mathrm{L}$$ container holds $$1.25\ \mathrm{mol} of H$_2 at$$ $$20^\circ\mathrm{C}$$ and $$0.50\ \mathrm{mol} of He at$$ $$20^\circ\mathrm{C}. $$What is the final pressure (in bar) after the two gases are combined in the same $$5.0\ \mathrm{L}$$ container? ($$R = 0.08314\ \mathrm{bar\ L\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$8.8\ \mathrm{bar}$$

Question 5

A sample of hydrogen gas is collected over water at $$25^\circ\mathrm{C}$$ and a total pressure of $$748.2\ \mathrm{Torr}. $$The vapor pressure of water at $$25^\circ\mathrm{C} is$$ $$23.78\ \mathrm{Torr}. $$What is the partial pressure of hydrogen gas?

Accepted Answer

$$724.4\ \mathrm{Torr}$$

Question 6

Which of the following best describes the mole fraction ($$X_i) of a $$component in a gas mixture?

Accepted Answer

$$X_i = \frac{n_i}{n_{\mathrm{total}}}$$

Question 7

A mixture of gases contains $$0.80\ \mathrm{mol} of N$_2$$, $$0.20\ \mathrm{mol} of O$_2$$, and $$0.10\ \mathrm{mol} of Ar. If $$the total pressure is $$2.0\ \mathrm{atm}$$, what is the partial pressure of O$$_2$$?

Accepted Answer

$$0.40\ \mathrm{atm}$$

Question 8

A chemical reaction produces hydrogen gas, which is collected over water at $$30^\circ\mathrm{C}$$ and a total pressure of $$760\ \mathrm{Torr}. $$The vapor pressure of water at $$30^\circ\mathrm{C} is$$ $$31.82\ \mathrm{Torr}. $$What is the pressure of the dry hydrogen gas?

Accepted Answer

$$728.18\ \mathrm{Torr}$$

Question 9

Which of the following statements about Dalton’s Law of Partial Pressures is correct?

Accepted Answer

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

Question 10

A $$10.0\ \mathrm{L}$$ vessel contains $$2.00\ \mathrm{mol} of O$_2$$ and $$3.00\ \mathrm{mol} of N$_2 at$$ $$27^\circ\mathrm{C}. $$What is the total pressure in the vessel? ($$R = 0.0821\ \mathrm{L\ atm\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$12.3\ \mathrm{atm}$$

Question 11

A $$250\ \mathrm{g}$$ sample of sodium azide ($$\mathrm{NaN}_3) is $$used in an automobile airbag. The decomposition reaction is $$2\mathrm{NaN}_3(s) \rightarrow 2\mathrm{Na}(s) + 3\mathrm{N}_2(g). $$Assuming STP conditions, what volume of nitrogen gas is produced?

Accepted Answer

$$122\ \mathrm{L}$$

Question 12

If the mole fraction of O$$_2 in a $$gas mixture is $$0.2$$ and the total pressure is $$5.0\ \mathrm{atm}$$, what is the partial pressure of O$$_2$$?

Accepted Answer

$$1.0\ \mathrm{atm}$$

Question 13

A $$5.0\ \mathrm{g}$$ sample of bronze contains $$1.0\ \mathrm{g} of $$tin and $$4.0\ \mathrm{g} of $$copper. What is the mass fraction of tin in the sample?

Accepted Answer

$$0.2$$

Question 14

A mixture of gases contains $$2.0\ \mathrm{mol} of He $$and $$3.0\ \mathrm{mol} of Ne. If $$the total pressure is $$4.0\ \mathrm{atm}$$, what is the partial pressure of He?

Accepted Answer

$$1.6\ \mathrm{atm}$$

Question 15

Which of the following is a correct application of Dalton’s Law when collecting a gas over water?

Accepted Answer

$$P_{\mathrm{total}} = P_{\mathrm{gas}} + P_{\mathrm{water\ vapor}}$$

Question 16

A $$10.0\ \mathrm{L}$$ container at $$27^\circ\mathrm{C}$$ contains $$0.50\ \mathrm{mol} of O$_2$$ and $$0.50\ \mathrm{mol} of N$_2. $$What is the mole fraction of O$$_2 in $$the mixture?

Accepted Answer

$$0.5$$

Question 17

A $$2.0\ \mathrm{L}$$ flask contains $$0.10\ \mathrm{mol} of CO$_2$$ and $$0.30\ \mathrm{mol} of N$_2 at$$ $$25^\circ\mathrm{C}. $$What is the partial pressure of CO$$_2$$? ($$R = 0.0821\ \mathrm{L\ atm\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$1.22\ \mathrm{atm}$$

Question 18

Which of the following best explains why the total pressure of a gas mixture increases when water vapor is added?

Accepted Answer

The water vapor exerts its own partial pressure, which adds to the total pressure.

Question 19

A $$1.00\ \mathrm{L}$$ container holds $$0.50\ \mathrm{mol} of O$_2 at$$ $$25^\circ\mathrm{C}. $$What is the pressure in the container? ($$R = 0.0821\ \mathrm{L\ atm\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$12.2\ \mathrm{atm}$$

Chapter 5.4: Gases – Mixtures, Dalton’s Law, and Stoichiometry of Gas Reactions

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