Q: Which of the following is the correct formula for percent composition by mass of an element in a compound?

$$\dfrac{\text{mass of element in 1 mol of compound}}{\text{molar mass of compound}} \times 100\%$$

Question 1

A sample of gas occupies $$31.0\ \mathrm{mL} at$$ $$372\ \mathrm{K}$$ and $$1.25\ \mathrm{atm}. $$What is the pressure of this gas when the volume is expanded to $$63.0\ \mathrm{mL}$$ and the temperature is increased to $$398\ \mathrm{K}$$? (Assume ideal gas behavior.)

Accepted Answer

$$0.98\ \mathrm{atm}$$

Question 2

Which of the following statements best explains why water ($$\mathrm{H_2O}) $$has a much higher boiling point than methane ($$\mathrm{CH_4$}$$)?

Accepted Answer

Water forms hydrogen bonds, which are much stronger than the London dispersion forces in methane.

Question 3

A $$12.0\ \mathrm{L}$$ gas cylinder contains $$0.70\ \mathrm{mol} of$$ $$\mathrm{C_4H_{10}} at$$ $$298\ \mathrm{K}. $$The pressure inside the cylinder is $$1.82\ \mathrm{atm}. $$What would be the temperature of the gas in $$^\circ\mathrm{C} if $$the gas is transferred into a $$6.0\ \mathrm{L}$$ cylinder at $$0.88\ \mathrm{atm}$$?

Accepted Answer

$$-58\ ^\circ\mathrm{C}$$

Question 4

Which of the following molecules is nonpolar, even though it contains polar bonds?

Accepted Answer

$$\mathrm{CO_2$}$$

Question 5

Which of the following is the correct Lewis structure for $$\mathrm{NO_3$^-} ($$nitrate ion)?

Accepted Answer

A structure with three equivalent N–O bonds, each with a bond order of $$1\frac{1}{3}$$, and the negative charge delocalized over the three oxygens.

Question 6

Which of the following best describes the relationship between pressure and volume for a fixed amount of gas at constant temperature (Boyle's Law)?

Accepted Answer

Pressure and volume are inversely proportional.

Question 7

A $$2.00\ \mathrm{g}$$ sample of a compound containing only carbon, hydrogen, and oxygen is combusted and produces $$2.93\ \mathrm{g} of$$ $$\mathrm{CO_2$}$$ and $$1.20\ \mathrm{g} of$$ $$\mathrm{H_2O}. $$What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{C_2H_4O_2}$$

Question 8

Which of the following statements about intermolecular forces is correct?

Accepted Answer

Hydrogen bonding occurs only when hydrogen is bonded to F, O, or N.

Question 9

A $$5.00\ \mathrm{L}$$ container holds $$0.250\ \mathrm{mol} of$$ $$\mathrm{O_2$}$$ gas at $$27^\circ\mathrm{C}. $$What is the pressure in the container? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$1.22\ \mathrm{atm}$$

Question 10

Which of the following best explains why ionic solids generally have higher melting points than molecular solids?

Accepted Answer

Ionic solids have stronger electrostatic attractions between ions than the intermolecular forces in molecular solids.

Question 11

Which of the following is the correct relationship for the density of a gas using the ideal gas law?

Accepted Answer

$$d = \dfrac{PM}{RT}$$

Question 12

A $$0.500\ \mathrm{mol}$$ sample of $$\mathrm{N_2$}$$ gas is collected over water at $$25^\circ\mathrm{C}$$ and a total pressure of $$755\ \mathrm{mmHg}. $$The vapor pressure of water at $$25^\circ\mathrm{C} is$$ $$24\ \mathrm{mmHg}. $$What is the partial pressure of $$\mathrm{N_2$}$$ gas?

Accepted Answer

$$731\ \mathrm{mmHg}$$

Question 13

Which of the following molecules has the highest boiling point?

Accepted Answer

$$\mathrm{NH_3$}$$

Question 14

Which of the following best describes the kinetic molecular theory of gases?

Accepted Answer

Gas particles are in constant, random motion and collisions between them are perfectly elastic.

Question 15

A $$10.0\ \mathrm{g}$$ sample of a compound contains $$4.0\ \mathrm{g} of $$carbon, $$1.0\ \mathrm{g} of $$hydrogen, and $$5.0\ \mathrm{g} of $$oxygen. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{C_2H_3O_2}$$

Question 16

Which of the following is the correct order of increasing strength of intermolecular forces?

Accepted Answer

London dispersion \u003c dipole-dipole \u003c hydrogen bonding

Question 17

Which of the following best describes the effect of increasing temperature on the solubility of gases in water?

Accepted Answer

The solubility of gases in water decreases as temperature increases.

Question 18

Which of the following is the correct formula for percent composition by mass of an element in a compound?

Accepted Answer

$$\dfrac{	ext{mass of element in 1 mol of compound}}{	ext{molar mass of compound}} 	imes 100\%$$

Question 19

Which of the following best explains why $$\mathrm{NH_3$} is $$polar while $$\mathrm{BF_3$} is $$nonpolar?

Accepted Answer

$$\mathrm{NH_3$}$$ has a trigonal pyramidal shape with a lone pair, while $$\mathrm{BF_3$} is $$trigonal planar and symmetric.

Question 20

Which of the following is the correct relationship for Dalton's Law of Partial Pressures?

Accepted Answer

$$P_{	ext{total}} = P_1$ + P_2$ + P_3$ + \ldots$$

General Chemistry Exam 2 Study Guide: Chapters 5, 6, and 8

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