Question 1

Which of the following statements best explains why the pH of pure water decreases as temperature increases above 25°C?

Accepted Answer

The value of $$K_w$$ increases with temperature, leading to higher $$[H_3O^+].$$

Question 2

A solution is prepared by mixing 50.0 mL of 0.20 M HCl and 50.0 mL of 0.10 M NaOH. What is the pH of the resulting solution?

Accepted Answer

$$pH = 1.3$$

Question 3

Which of the following best describes the relationship between $$pH$$, $$pOH$$, and $$pK_w at 25$$°C?

Accepted Answer

$$pH + pOH = 14$$

Question 4

A 0.15 M solution of acetic acid ($$K_a = 1.8 	imes 10$$^{-5}$$) has a pH of approximately:

Accepted Answer

$$pH = 2.78$$

Question 5

Which of the following best explains why $$ClO_4$$^-$$ is a very weak conjugate base?

Accepted Answer

It is stabilized by resonance and inductive effects from multiple electronegative atoms.

Question 6

Which of the following mixtures will result in a buffer solution?

Accepted Answer

Mixing equal moles of a weak acid and its conjugate base.

Question 7

What is the pH of a buffer solution containing 0.20 M acetic acid and 0.10 M sodium acetate? ($$K_a of $$acetic acid = $$1.8 	imes 10$$^{-5}$$)

Accepted Answer

$$pH = 4.4$$

Question 8

Which of the following best describes the effect of adding a small amount of strong acid to a buffer solution containing HF and NaF?

Accepted Answer

The $$F^-$$ ions react with the added acid, minimizing the change in pH.

Question 9

A student titrates a weak acid with a strong base. At the half-equivalence point, which of the following is true?

Accepted Answer

$$pH = pK_a$$

Question 10

Which of the following best explains why the solubility of $$Mg(OH)_2$$ increases in an acidic environment?

Accepted Answer

Added $$H^+$$ reacts with $$OH^-$$, shifting the equilibrium to dissolve more $$Mg(OH)_2.$$

Question 11

Which of the following is a correct application of the Henderson-Hasselbalch equation?

Accepted Answer

$$pH = pK_a + \log \left( \frac{[A^-]}{[HA]} \right)$$

Question 12

Which of the following best describes the buffer capacity of a solution?

Accepted Answer

It is greater when the concentrations of both buffer components are higher.

Question 13

Which of the following ions would NOT significantly affect the pH of a solution?

Accepted Answer

$$Na^+$$

Question 14

A buffer is made by mixing 0.40 M HF and 0.40 M NaF. What is the pH if $$K_a$$ for HF is $$6.8 	imes 10$$^{-4}$$?

Accepted Answer

$$pH = 3.17$$

Question 15

Which of the following best describes the effect of pH on the solubility of a salt containing a weak base anion?

Accepted Answer

Lowering the pH increases solubility by reacting with the basic anion.

Question 16

Which of the following best explains why carboxylic acids are weak acids?

Accepted Answer

Their conjugate bases are stabilized by resonance, but not enough to make them strong acids.

Question 17

A solution has $$[OH^-] = 2.79 	imes 10$$^{-15}$$ M at 25°C. What is the pH?

Accepted Answer

$$pH = -0.6$$

Question 18

Which of the following best describes the major species present at the equivalence point in the titration of a weak acid with a strong base?

Accepted Answer

The conjugate base of the weak acid

Question 19

Which of the following indicators would be most appropriate for detecting the equivalence point in the titration of a strong acid with a strong base?

Accepted Answer

Bromothymol blue ($$pK_a \approx 7)$$

Unit 8: Acids and Bases – General Chemistry Study Notes

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