Question 1

Which of the following statements best explains why the pH of a buffer solution remains relatively constant upon the addition of small amounts of acid or base?

Accepted Answer

The buffer contains a weak acid and its conjugate base, which react with added H$$^+ or OH$^- to $$minimize pH changes.

Question 2

A solution is prepared by mixing 0.10 mol of acetic acid (CH$$_3$$COOH, $$K_a = 1.8 	imes 10$$^{-5}$$) and 0.10 mol of sodium acetate (CH_3$COONa) in enough water to make 1.0 L of solution. What is the pH of this buffer solution?

Accepted Answer

$$	ext{pH} = 4.74$$

Question 3

Which salt, when dissolved in water, will produce a basic solution?

Accepted Answer

Sodium acetate (CH$$_3$$COONa)

Question 4

A student adds 0.0050 mol of NaOH to 100.0 mL of a buffer containing 0.01 mol acetic acid and 0.01 mol sodium acetate. What is the change in pH, approximately?

Accepted Answer

The pH increases only slightly, demonstrating buffer action.

Question 5

Which of the following best describes the effect of increasing the concentration of CO$$_2 in $$ocean water on the solubility of calcium carbonate (CaCO$$_3$$)?

Accepted Answer

The solubility of CaCO$$_3$$ increases because more H$$_2CO$_3$$ forms, shifting equilibrium.

Question 6

Which of the following combinations would create the most effective buffer solution for maintaining a pH near 7.4 (the pH of blood)?

Accepted Answer

Carbonic acid and sodium bicarbonate

Question 7

A 0.02 M solution of NaOH is prepared. What is the pH of this solution?

Accepted Answer

$$	ext{pH} = 12.3$$

Question 8

Which of the following best explains why the addition of sodium phosphate to water pipes can decrease the concentration of lead in drinking water?

Accepted Answer

Sodium phosphate reacts with lead ions to form insoluble lead(II) phosphate, reducing [Pb$$^{2+}$$] in solution.

Question 9

Which of the following reactions will result in an increase in entropy ($$\Delta S \u003e 0$$)?
I. $$2 	ext{NH}_3(g) ightarrow 	ext{N}_2(g) + 3 	ext{H}_2(g)
II$$. $$2 	ext{H}_2O(l) ightarrow 2 	ext{H}_2(g) + 	ext{O}_2(g)$$
III. $$	ext{CaH}_2(s) + 2 	ext{H}_2O(l) ightarrow 	ext{Ca(OH)}_2(s) + 2 	ext{H}_2(g)$$

Accepted Answer

Three of these

Question 10

Which of the following molecules has the largest molar entropy?

Accepted Answer

CO$$_2(g)$$

Question 11

For the reaction $$3 	ext{H}_2(g) + 	ext{N}_2(g) ightleftharpoons 2 	ext{NH}_3(g)$$, $$\Delta H = -92 kJ/$$mol and $$\Delta S = -198.45 J/$$mol·K. At what temperature, if any, is this reaction spontaneous?

Accepted Answer

Only if the temperature is below 463 K

Question 12

Which of the following best describes the relationship between $$K_a$$ and $$K_b$$ for a conjugate acid-base pair?

Accepted Answer

$$K_a 	imes K_b = K_w$$

Question 13

A solution is made by dissolving 2.0 mol of sodium acetate in 4.0 L of water. Given $$K_a$$ for acetic acid is $$2.0 	imes 10$$^{-5}$$, what is the pH of the solution?

Accepted Answer

pH \u003e 7, because acetate acts as a weak base

Question 14

Which of the following best describes the effect of adding a common ion to a saturated solution of a sparingly soluble salt?

Accepted Answer

The solubility of the salt decreases due to the common ion effect.

Question 15

Which of the following best explains why ocean acidification is harmful to marine organisms such as corals and mollusks?

Accepted Answer

Lower pH increases the solubility of CaCO$$_3$$, making it harder for organisms to build shells and skeletons.

Question 16

Which of the following is true about the equivalence point in the titration of a weak base with a strong acid?

Accepted Answer

The pH at the equivalence point is less than 7.

Question 17

Which of the following best describes the effect of increasing the pH on the solubility of Mg(OH)$$_2$$?

Accepted Answer

The solubility decreases because of the common ion effect from added OH$$^-.$$

Question 18

Which of the following best describes the relationship between Gibbs free energy and the equilibrium constant $$K$$?

Accepted Answer

$$\Delta G^\circ = -RT \ln K$$

Acids, Bases, Buffers, and Thermodynamics: Advanced Equilibrium and Solution Chemistry

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