Question 1

Which of the following best describes the role of water (H$_2$O) as an acid in the Brønsted-Lowry theory?

Accepted Answer

It loses a proton, so it is a proton donor.

Question 2

Given the following equilibrium: $\mathrm{H_2BO_3^- (aq) + H_2O (l) \rightleftharpoons H_3BO_3 (aq) + OH^- (aq)}$, what is the $K_b$ expression for this reaction?

Accepted Answer

$K_b = \dfrac{[H_3BO_3][OH^-]}{[H_2BO_3^-]}$

Question 3

A 0.27 M solution of acetic acid ($\mathrm{CH_3COOH}$) has a $K_a$ of $1.3 	imes 10^{-5}$. What is the pH at equilibrium?

Accepted Answer

2.73

Question 4

Which of the following salts will have a pH less than 7 when dissolved in water?

Accepted Answer

NH$_4$NO$_3$

Question 5

A solution containing caffeine ($\mathrm{C_8H_{10}N_4O_2}$) has a hydroxide concentration of $7.29 	imes 10^{-6}$ M at equilibrium. What is the pH? Is it an acidic, basic, or neutral solution?

Accepted Answer

8.86, basic

Question 6

Which of the following pairs of compounds will form a buffer and have the greatest buffer capacity when combined?

Accepted Answer

0.10 M CH$_3$COOH and 0.25 M CH$_3$COONa

Question 7

If 42.0 mL of 0.100 M NaOH is required to completely neutralize 100.0 mL of triprotic phosphoric acid ($\mathrm{H_3PO_4}$) solution, what is the concentration of the acid?

Accepted Answer

0.1240 M

Question 8

A weak acid solution has a pH of 5.13. What is the $[H_3O^+]$ concentration?

Accepted Answer

$1.3 	imes 10^{-5}$ M

Question 9

What is the percent ionization of a 0.27 M solution of acetic acid ($K_a = 1.3 	imes 10^{-5}$)?

Accepted Answer

0.089%

Question 10

Which of the following statements is true regarding the relationship between $K_a$, $K_b$, and $K_w$?

Accepted Answer

$K_a 	imes K_b = K_w$

Question 11

If the $pK_a$ of an acid is 7.52 and the $pK_b$ of its conjugate base is 6.64, what is the value of $pK_w$?

Accepted Answer

$pK_w = 14.16$

Question 12

A buffer solution is made by mixing 0.100 M acetic acid and 0.100 M sodium acetate. If the $K_a$ for acetic acid is $1.8 	imes 10^{-5}$, what is the pH of the buffer?

Accepted Answer

4.74

Question 13

Which of the following is the correct equilibrium constant expression for the weak acid $\mathrm{HC_2H_3O_2}$?

Accepted Answer

$K_a = \dfrac{[C_2H_3O_2^-][H_3O^+]}{[HC_2H_3O_2]}$

Question 14

A weak acid solution has a $pH$ of 4.88. What is the $[H_3O^+]$ concentration?

Accepted Answer

$1.3 	imes 10^{-5}$ M$

Question 15

A buffer solution is prepared by mixing 0.100 M NH$_3$ and 0.100 M NH$_4$Cl. If the $K_b$ for NH$_3$ is $1.8 	imes 10^{-5}$, what is the pH of the buffer?

Accepted Answer

9.25

Question 16

If 10.00 mL of 0.103 M HClO solution is titrated by 2.06 mL of 0.500 M NaOH solution, what is the pH at this point in the titration? Is the solution acidic, neutral, or basic?

Accepted Answer

7.00, neutral

Question 17

When a small amount of highly soluble NaOH is added to a solution of weak acid NH$_4$NO$_3$, what will happen to the pH value after the following neutralization reaction: $\mathrm{NH_4^+ (aq) + OH^- (aq) \rightarrow NH_3 (aq) + H_2O (l)}$?

Accepted Answer

The pH value will increase since [OH$^-$] decreases.

Question 18

Given the following titration graph, Unknown 1 has an equivalence point at pH 7.0 and Unknown 2 at pH 2.0. What can you determine about these two unknown samples?

Accepted Answer

Unknown 1 is a stronger acid than Unknown 2, so $K_a$ is greater than $K_a$.

Question 19

A buffer solution is made by mixing 0.100 M acetic acid and 0.100 M sodium acetate. If the $K_a$ for acetic acid is $1.8 	imes 10^{-5}$, what is the pH of the buffer?

Accepted Answer

4.74

Acids, Bases, Buffers, and Equilibrium: General Chemistry Study Guide

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