Q: A solution has a pH of 4.5. What is the $[\mathrm{H_3O^+}]$ concentration?

$3.2 \times 10^{-5}\ \mathrm{M}$

Q: Which of the following is the correct relationship between $K_a$ and $K_b$ for a conjugate acid-base pair?

$K_a \times K_b = 1 \times 10^{-14}$

Question 1

Which of the following best describes a Brønsted-Lowry acid?

Accepted Answer

A substance that donates a proton.

Question 2

Given the reaction: $\mathrm{NH_4^+ (aq) + OH^- (aq) \rightarrow NH_3 (aq) + H_2O (l)}$, which species acts as the Brønsted-Lowry acid?

Accepted Answer

$\mathrm{NH_4^+}$

Question 3

Which of the following is a correct expression for the acid dissociation constant ($K_a$) for acetic acid ($\mathrm{CH_3COOH}$)?

Accepted Answer

$K_a = \frac{[\mathrm{H_3O^+}][\mathrm{CH_3COO^-}]}{[\mathrm{CH_3COOH}]}$

Question 4

A solution has a pH of 4.5. What is the $[\mathrm{H_3O^+}]$ concentration?

Accepted Answer

$3.2 	imes 10^{-5}\ \mathrm{M}$

Question 5

Which of the following statements about strong acids is correct?

Accepted Answer

Strong acids have a high $K_a$ value and dissociate completely in water.

Question 6

Calculate the pH of an aqueous ammonia solution with $[\mathrm{OH^-}] = 0.0019\ \mathrm{M}$.

Accepted Answer

pH = 11.28

Question 7

Which of the following is a Lewis acid in the reaction $\mathrm{BF_3 + F^- \rightarrow BF_4^-}$?

Accepted Answer

$\mathrm{BF_3}$

Question 8

If the $K_a$ for acetic acid is $1.8 	imes 10^{-5}$, what is the $pK_a$?

Accepted Answer

$pK_a = 4.7$

Question 9

A 0.010 M solution of a weak acid HA has a pH of 5.0. What is the degree of ionization of HA?

Accepted Answer

0.1 %

Question 10

Which of the following pairs correctly matches the stronger acid in water?

Accepted Answer

HIO$_3$ ($pK_a = 0.77$) is stronger than HF ($pK_a = 3.45$)

Question 11

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

Accepted Answer

$K_a 	imes K_b = 1 	imes 10^{-14}$

Question 12

Calculate the $pK_b$ for the conjugate base of acetic acid ($K_a = 1.8 	imes 10^{-5}$).

Accepted Answer

$pK_b = 9.3$

Question 13

Which of the following best describes a Lewis base?

Accepted Answer

A substance that donates an electron pair.

Question 14

If $[\mathrm{H_3O^+}] = 1.0 	imes 10^{-7}\ \mathrm{M}$ and $[\mathrm{OH^-}] = 1.0 	imes 10^{-7}\ \mathrm{M}$ at 25°C, what is the pH of the solution?

Accepted Answer

pH = 7

Question 15

Which of the following solutions is most likely to have a pH less than 7?

Accepted Answer

A solution of HCl

Question 16

Which of the following statements is true regarding the equilibrium of a weak acid in water?

Accepted Answer

The equilibrium favors the reactants.

Question 17

Calculate the $pK_a$ for the conjugate acid of pyridine ($K_b = 1.8 	imes 10^{-9}$).

Accepted Answer

$pK_a = 5.25$

Question 18

Which of the following is the stronger base in water: NO$_2^-$ ($pK_b = 10.63$) or CN$^-$ ($pK_b = 4.69$)?

Accepted Answer

CN$^-$

Question 19

In the reaction $\mathrm{HNO_2(aq) + HCO_3^-(aq) ightleftharpoons NO_3^-(aq) + H_2CO_3(aq)}$, which side is favored at equilibrium? ($K_a$ for HNO$_2$ = $7.2 	imes 10^{-4}$, $K_a$ for H$_2$CO$_3$ = $1.8 	imes 10^{-4}$)

Accepted Answer

The left side (reactants)

Acid-Base Equilibria: Concepts, Calculations, and Applications

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