Q: A solution is prepared by dissolving 5.85 g of NaCl (molar mass = 58.5 g/mol) in enough water to make 0.500 L of solution. What is the molarity of the solution?

$$M = \frac{\text{moles of solute}}{\text{liters of solution}} = \frac{5.85/58.5}{0.500} = 0.2\ \mathrm{M}$$

Question 1

Which of the following statements best explains why sodium (Na) reacts vigorously with water, while magnesium (Mg) reacts much less vigorously under similar conditions?

Accepted Answer

Sodium has a lower ionization energy than magnesium, so it loses its valence electron more easily.

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 will be the new volume of the gas? (Assume ideal gas behavior.)

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$P_2$$ $$T_1$$} = \frac{(1.00\ \mathrm{atm})(2.50\ \mathrm{L})(150\ \mathrm{K})}{(2.00\ \mathrm{atm})(300\ \mathrm{K})} = 0.625\ \mathrm{L}$$

Question 3

Which of the following electron configurations represents a ground state atom of sulfur (S, atomic number 16)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^4$$

Question 4

Which of the following best describes the molecular geometry of methane ($$CH_4) $$according to VSEPR theory?

Accepted Answer

Tetrahedral

Question 5

A solution is prepared by dissolving 5.85 g of NaCl (molar mass = 58.5 g/mol) in enough water to make 0.500 L of solution. What is the molarity of the solution?

Accepted Answer

$$M = \frac{	ext{moles of solute}}{	ext{liters of solution}} = \frac{5.85/58.5}{0.500} = 0.2\ \mathrm{M}$$

Question 6

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have the same number of valence electrons.

Question 7

Which of the following is the correct balanced equation for the combustion of propane ($$C_3H_8) in $$oxygen?

Accepted Answer

$$C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$$

Question 8

Which of the following best describes the difference between a strong acid and a weak acid?

Accepted Answer

A strong acid completely ionizes in water, while a weak acid only partially ionizes.

Question 9

A chemical reaction has $$\Delta H = -125\ \mathrm{kJ}$$ and $$\Delta S = +50\ \mathrm{J/K}. At $$what temperature (in K) does the reaction change from spontaneous to non-spontaneous? ($$\Delta G = \Delta H - T\Delta S)$$

Accepted Answer

$$T = \frac{\Delta H}{\Delta S} = \frac{125,000\ \mathrm{J}}{50\ \mathrm{J/K}} = 2500\ \mathrm{K}$$

Question 10

Which of the following is a correct statement about the quantum mechanical model of the atom?

Accepted Answer

Electrons are found in regions of high probability called orbitals.

Question 11

A patient receives an intravenous solution containing 0.9% NaCl (normal saline). Which property of this solution makes it suitable for medical use?

Accepted Answer

It is isotonic with human blood plasma.

Question 12

Which of the following compounds is most likely to have hydrogen bonding as its strongest intermolecular force?

Accepted Answer

$$H_2O$$

Question 13

Which of the following best describes the process of neutralization?

Accepted Answer

A reaction between an acid and a base to produce a salt and water.

Question 14

Which of the following statements about organic compounds is correct?

Accepted Answer

Organic compounds are primarily composed of carbon and hydrogen.

Question 15

A sample contains 0.50 mol of $$O_2$$ gas at 25°C and 1.00 atm. What is the volume of the gas? (Use $$R = 0.0821\ \mathrm{L\ atm\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$V = \frac{nRT}{P} = \frac{0.50 	imes 0.0821 	imes 298}{1.00} = 12.2\ \mathrm{L}$$

Question 16

Which of the following best explains why ice floats on liquid water?

Accepted Answer

Ice is less dense than liquid water due to the hydrogen-bonded open structure in the solid state.

Question 17

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

Accepted Answer

$$H^+ (aq) + OH^- (aq) \rightarrow H_2O (l)$$

Question 18

Which of the following statements about chemical equilibrium is correct?

Accepted Answer

At equilibrium, the rates of the forward and reverse reactions are equal.

Question 19

Which of the following best describes the role of a catalyst in a chemical reaction?

Accepted Answer

A catalyst increases the rate of a reaction by providing an alternative pathway with lower activation energy.

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