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

A substance that donates a proton (H$^+$) to another species.

Q: A solution has a pOH of 3.25. What is the concentration of hydroxide ions, [OH$^-$]?

$[\mathrm{OH}^-] = 10^{-3.25} = 5.62 \times 10^{-4}\ \mathrm{M}$

Q: Calculate the percent ionization of a 0.10 M acetic acid (CH$_3$COOH) solution if [H$_3$O$^+$] at equilibrium is $4.2 \times 10^{-3}$ M.

$\%\ \mathrm{ionization} = \frac{4.2 \times 10^{-3}}{0.10} \times 100\% = 4.2\%$

Q: A 0.10 M solution of ammonia (NH$_3$) has a $K_b$ of $1.8 \times 10^{-5}$. What is the pH of the solution? (Assume $x \ll 0.10$)

$[\mathrm{OH}^-] = \sqrt{(0.10)(1.8 \times 10^{-5})} = 1.34 \times 10^{-3}\ \mathrm{M}$;\ pOH = -\log(1.34 \times 10^{-3}) = 2.87;\ pH = 14 - 2.87 = 11.13$

Q: Which of the following acids is the strongest, and why?

HClO$_4$, because it has the most oxygen atoms, which stabilize the negative charge on the conjugate base.

Q: A 0.25 M solution of a weak acid, HA, has a pH of 2.70. What is the acid dissociation constant, $K_a$, for HA?

$[H_3O^+] = 10^{-2.70} = 2.0 \times 10^{-3}\ \mathrm{M}$;\ K_a = \frac{(2.0 \times 10^{-3})^2}{0.25 - 2.0 \times 10^{-3}} \approx 1.6 \times 10^{-5}$

Q: Which of the following best explains why HF is a weak acid, while HCl is a strong acid?

The F$^-$ ion is small and highly electronegative, so it holds onto the proton more tightly, making HF less likely to dissociate.

Q: What is the pH of a solution formed by mixing 50.0 mL of 0.150 M HBr with 25.0 mL of 0.020 M HCl? (Assume both are strong acids.)

First, calculate total moles of H$_3$O$^+$: $0.0500\ \mathrm{L} \times 0.150\ \mathrm{M} = 0.0075\ \mathrm{mol}$ (HBr), $0.0250\ \mathrm{L} \times 0.020\ \mathrm{M} = 0.0005\ \mathrm{mol}$ (HCl). Total moles = $0.0080$ mol. Total volume = $0.0750$ L. $[H_3O^+] = \frac{0.0080}{0.0750} = 0.107\ \mathrm{M}$. $\mathrm{pH} = -\log(0.107) = 0.97$

Question 1

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

Accepted Answer

A substance that donates a proton (H$^+$) to another species.

Question 2

A 0.040 M solution of HClO$_4$ (a strong acid) is prepared. What is the pH of the solution?

Accepted Answer

$\mathrm{pH} = -\log(0.040) = 1.40$

Question 3

Which of the following is the conjugate base of HSO$_4^-$?

Accepted Answer

SO$_4^{2-}$

Question 4

A solution has a pOH of 3.25. What is the concentration of hydroxide ions, [OH$^-$]?

Accepted Answer

$[\mathrm{OH}^-] = 10^{-3.25} = 5.62 	imes 10^{-4}\ \mathrm{M}$

Question 5

Which of the following salts will produce a basic solution when dissolved in water?

Accepted Answer

NaF

Question 6

Calculate the percent ionization of a 0.10 M acetic acid (CH$_3$COOH) solution if [H$_3$O$^+$] at equilibrium is $4.2 \times 10^{-3}$ M.

Accepted Answer

$\%\ \mathrm{ionization} = \frac{4.2 	imes 10^{-3}}{0.10} 	imes 100\% = 4.2\%$

Question 7

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

Accepted Answer

$K_a 	imes K_b = K_w$

Question 8

A 0.10 M solution of ammonia (NH$_3$) has a $K_b$ of $1.8 \times 10^{-5}$. What is the pH of the solution? (Assume $x \ll 0.10$)

Accepted Answer

$[\mathrm{OH}^-] = \sqrt{(0.10)(1.8 	imes 10^{-5})} = 1.34 	imes 10^{-3}\ \mathrm{M}$;\ pOH = -\log(1.34 	imes 10^{-3}) = 2.87;\ pH = 14 - 2.87 = 11.13$

Question 9

Which of the following is a Lewis acid?

Accepted Answer

BF$_3$

Question 10

Which of the following acids is the strongest, and why?

Accepted Answer

HClO$_4$, because it has the most oxygen atoms, which stabilize the negative charge on the conjugate base.

Question 11

A 0.25 M solution of a weak acid, HA, has a pH of 2.70. What is the acid dissociation constant, $K_a$, for HA?

Accepted Answer

$[H_3O^+] = 10^{-2.70} = 2.0 	imes 10^{-3}\ \mathrm{M}$;\ K_a = \frac{(2.0 	imes 10^{-3})^2}{0.25 - 2.0 	imes 10^{-3}} \approx 1.6 	imes 10^{-5}$

Question 12

Which of the following best explains why HF is a weak acid, while HCl is a strong acid?

Accepted Answer

The F$^-$ ion is small and highly electronegative, so it holds onto the proton more tightly, making HF less likely to dissociate.

Question 13

What is the pH of a solution formed by mixing 50.0 mL of 0.150 M HBr with 25.0 mL of 0.020 M HCl? (Assume both are strong acids.)

Accepted Answer

First, calculate total moles of H$_3$O$^+$: $0.0500\ \mathrm{L} \times 0.150\ \mathrm{M} = 0.0075\ \mathrm{mol}$ (HBr), $0.0250\ \mathrm{L} \times 0.020\ \mathrm{M} = 0.0005\ \mathrm{mol}$ (HCl). Total moles = $0.0080$ mol. Total volume = $0.0750$ L. $[H_3O^+] = \frac{0.0080}{0.0750} = 0.107\ \mathrm{M}$. $\mathrm{pH} = -\log(0.107) = 0.97$

Question 14

Which of the following best describes an amphiprotic substance?

Accepted Answer

A substance that can act as either a proton donor or a proton acceptor.

Question 15

A 0.10 M solution of a weak base, B, has a $K_b$ of $2.5 	imes 10^{-5}$. What is the pH of the solution? (Assume $x \ll 0.10$)

Accepted Answer

$[OH^-] = \sqrt{(0.10)(2.5 	imes 10^{-5})} = 1.58 	imes 10^{-3}\ \mathrm{M}$;\ pOH = -\log(1.58 	imes 10^{-3}) = 2.80;\ pH = 14 - 2.80 = 11.20$

Question 16

Which of the following solutions will have the lowest pH?

Accepted Answer

0.10 M HNO$_3$

Question 17

Which of the following best explains why the pH of a 0.10 M solution of H$_2$SO$_4$ is not exactly 1.00?

Accepted Answer

The second ionization of H$_2$SO$_4$ is not complete, so the total [H$_3$O$^+$] is slightly less than 0.20 M.

Chapter 16: Acid-Base Equilibria – Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards