Q: A sample of gas occupies 2.50 L at 1.00 atm and 300 K. If the pressure is increased to 2.00 atm and the temperature is decreased to 150 K, what is the new volume of the gas? (Assume ideal gas behavior.)

$$V_2$$ = $$V_1$$ \times \frac{$$P_1$$}{$$P_2$$} \times \frac{$$T_2$$}{$$T_1$$} = 2.50\,\text{L} \times \frac{1.00}{2.00} \times \frac{150}{300} = 0.625\,\text{L}$$

Q: A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 500.0 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

$$M = \frac{\text{moles of solute}}{\text{liters of solution}} = \frac{10.0\,\text{g} / 58.44\,\text{g/mol}}{0.500\,\text{L}} = 0.342\,\text{M}$$

Q: A patient receives 500 mg of a medication. If the molar mass of the drug is 250 g/mol, how many moles of the drug did the patient receive?

$$\text{moles} = \frac{0.500\,\text{g}}{250\,\text{g/mol}} = 0.00200\,\text{mol}$$

Q: Which of the following is the correct balanced equation for the combustion of methane ($$\text{CH}_4) in $$oxygen?

$$\text{CH}_4 + 2\,\text{O}_2 \rightarrow \text{CO}_2 + 2\,\text{H}_2\text{O}$$

Q: Which of the following statements about acids and bases is correct according to the Arrhenius definition?

An acid produces $$\text{H}^+$$ ions in aqueous solution, while a base produces $$\text{OH}^-$$ ions.

Question 1

Which of the following best explains why water is considered a polar molecule?

Accepted Answer

Because the oxygen atom has a higher electronegativity than hydrogen, creating a partial negative charge on oxygen and a partial positive charge on hydrogen.

Question 2

A sample of gas occupies 2.50 L at 1.00 atm and 300 K. If the pressure is increased to 2.00 atm and the temperature is decreased to 150 K, what is the new volume of the gas? (Assume ideal gas behavior.)

Accepted Answer

$$V_2$$ = $$V_1$$ 	imes \frac{$$P_1$$}{$$P_2$$} 	imes \frac{$$T_2$$}{$$T_1$$} = 2.50\,	ext{L} 	imes \frac{1.00}{2.00} 	imes \frac{150}{300} = 0.625\,	ext{L}$$

Question 3

Which of the following statements about ionic and molecular compounds is correct?

Accepted Answer

Ionic compounds generally have higher melting points than molecular compounds due to strong electrostatic forces between ions.

Question 4

A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 500.0 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

Accepted Answer

$$M = \frac{	ext{moles of solute}}{	ext{liters of solution}} = \frac{10.0\,	ext{g} / 58.44\,	ext{g/mol}}{0.500\,	ext{L}} = 0.342\,	ext{M}$$

Question 5

Which of the following best describes the energy change when ice melts to form liquid water?

Accepted Answer

It is an endothermic process because energy is absorbed to break hydrogen bonds.

Question 6

Which of the following elements has the highest first ionization energy?

Accepted Answer

Neon ($$	ext{Ne})$$

Question 7

A patient receives 500 mg of a medication. If the molar mass of the drug is 250 g/mol, how many moles of the drug did the patient receive?

Accepted Answer

$$	ext{moles} = \frac{0.500\,	ext{g}}{250\,	ext{g/mol}} = 0.00200\,	ext{mol}$$

Question 8

Which of the following best explains why salt (NaCl) dissolves in water?

Accepted Answer

The positive and negative ions in NaCl are attracted to the partial charges on the polar water molecules, causing the ions to separate and disperse.

Question 9

Which of the following is the correct balanced equation for the combustion of methane ($$	ext{CH}_4) in $$oxygen?

Accepted Answer

$$	ext{CH}_4 + 2\,	ext{O}_2 ightarrow 	ext{CO}_2 + 2\,	ext{H}_2	ext{O}$$

Question 10

Which of the following statements about acids and bases is correct according to the Arrhenius definition?

Accepted Answer

An acid produces $$	ext{H}^+$$ ions in aqueous solution, while a base produces $$	ext{OH}^-$$ ions.

Question 11

A 2.00 L container holds 0.500 mol of $$	ext{O}_2$$ gas at 300 K. What is the pressure in the container? ($$R = 0.0821\,	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K})$$

Accepted Answer

Question 12

Which of the following best describes the trend in atomic radius across a period in the periodic table?

Accepted Answer

Atomic radius decreases from left to right due to increasing nuclear charge.

Question 13

Which of the following is a chemical change?

Accepted Answer

Iron rusting in moist air.

Question 14

A sample contains 3.01 $$	imes 10$^{23}$$ molecules of carbon dioxide. What is the mass of the sample? (Molar mass of CO$$_2 = 44.0 g/$$mol)

Accepted Answer

$$	ext{mass} = \frac{3.01 	imes 10$$^{23}$$}{6.02 	imes 10$$^{23}$$} 	imes 44.0 = 22.0\,	ext{g}$$

Question 15

Which of the following best explains why diamond is harder than graphite, even though both are forms of carbon?

Accepted Answer

Diamond has a three-dimensional network of covalent bonds, while graphite has layers held together by weak forces.

Question 16

Which of the following is the correct net ionic equation for the reaction between hydrochloric acid and sodium hydroxide?

Accepted Answer

$$	ext{H}^+ (aq) + 	ext{OH}^- (aq) ightarrow 	ext{H}_2	ext{O} (l)$$

Question 17

A 250 mL sample of a 0.200 M HCl solution is completely neutralized by 0.100 M NaOH. What volume of NaOH is required?

Accepted Answer

$$	ext{moles HCl} = 0.250 	imes 0.200 = 0.0500\,	ext{mol}$$; 	ext{moles NaOH} = 0.0500\,	ext{mol}; 	ext{volume} = \frac{0.0500}{0.100} = 0.500\,	ext{L} = 500\,	ext{mL}$

Question 18

Which of the following best describes the difference between a physical and a chemical property?

Accepted Answer

A physical property can be observed without changing the substance's identity, while a chemical property describes how a substance reacts with other substances.

Question 19

Which of the following is the correct electron configuration for a neutral atom of phosphorus ($$Z=15$$)?

Accepted Answer

$$1s^2$$\,$$2s^2$$\,$$2p^6$$\,$$3s^2$$\,$$3p^3$$

Introductory Chemistry: Core Topics and Study Guide

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