Q: What is the pH of a solution with $$[H^+] = 2.5 \times 10$$^{-4}$$\ M$$?

$$pH = -\log(2.5 \times 10$$^{-4}$$) = 3.60$$

Q: A 0.10 M solution of a weak acid, HA, has a pH of 3.00. What is the acid dissociation constant $$K_a$$ for HA?

$$K_a = \frac{[H^+][A^-]}{[HA]} = \frac{(1.0 \times 10$$^{-3}$$)^2$$}{0.10 - 1.0 \times $$10^{-3}$$} \approx 1.0 \times $$10^{-5}$

Q: Calculate the pOH of a solution with $$[OH^-] = 3.2 \times 10$$^{-5}$$\ M.$$

$$pOH = -\log(3.2 \times 10$$^{-5}$$) = 4.49$$

Q: A 0.20 M solution of a weak base, B, has a $$K_b = 1.8 \times 10$$^{-5}$$. What is the $$[OH^-]$$ at equilibrium? (Assume x$ is small compared to 0.20)

$$[OH^-] = \sqrt{K_b \times [B]} = \sqrt{1.8 \times 10$$^{-5}$$ \times 0.20} = 1.9 \times 10$$^{-3}$$\ M$$

Q: A student prepares a 0.10 M solution of formic acid ($$HCOOH) $$and measures its pH to be 2.38. What is the percent ionization of the acid?

Percent ionization $$= \frac{[H^+]}{[HCOOH]_{initial}} \times 100 = \frac{4.2 \times 10$$^{-3}$$}{0.10} \times 100 = 4.2\%$$

Question 1

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

Accepted Answer

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

Question 2

Which of the following pairs are conjugate acid-base pairs?

Accepted Answer

$$NH_4$$^+$$ and NH_3$

Question 3

What is the pH of a solution with $$[H^+] = 2.5 	imes 10$$^{-4}$$\ M$$?

Accepted Answer

$$pH = -\log(2.5 	imes 10$$^{-4}$$) = 3.60$$

Question 4

Which of the following is an amphiprotic species?

Accepted Answer

$$HSO_4$$^-$$

Question 5

A 0.10 M solution of a weak acid, HA, has a pH of 3.00. What is the acid dissociation constant $$K_a$$ for HA?

Accepted Answer

$$K_a = \frac{[H^+][A^-]}{[HA]} = \frac{(1.0 	imes 10$$^{-3}$$)^2$$}{0.10 - 1.0 	imes $$10^{-3}$$} \approx 1.0 	imes $$10^{-5}$

Question 6

Which of the following statements about strong acids is correct?

Accepted Answer

Strong acids dissociate completely in aqueous solution.

Question 7

Calculate the pOH of a solution with $$[OH^-] = 3.2 	imes 10$$^{-5}$$\ M.$$

Accepted Answer

$$pOH = -\log(3.2 	imes 10$$^{-5}$$) = 4.49$$

Question 8

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

Accepted Answer

Sodium acetate, $$CH_3COONa$$

Question 9

Given $$K_w = 1.0 	imes 10$$^{-14}$$ at 25°C, what is the relationship between K_a$ and K_b$ for a conjugate acid-base pair?

Accepted Answer

$$K_a 	imes K_b = K_w$$

Question 10

A 0.20 M solution of a weak base, B, has a $$K_b = 1.8 	imes 10$$^{-5}$$. What is the $$[OH^-]$$ at equilibrium? (Assume x$ is small compared to 0.20)

Accepted Answer

$$[OH^-] = \sqrt{K_b 	imes [B]} = \sqrt{1.8 	imes 10$$^{-5}$$ 	imes 0.20} = 1.9 	imes 10$$^{-3}$$\ M$$

Question 11

Which of the following is NOT a strong acid?

Accepted Answer

Acetic acid, $$CH_3COOH$$

Question 12

A student prepares a 0.10 M solution of formic acid ($$HCOOH) $$and measures its pH to be 2.38. What is the percent ionization of the acid?

Accepted Answer

Percent ionization $$= \frac{[H^+]}{[HCOOH]_{initial}} 	imes 100 = \frac{4.2 	imes 10$$^{-3}$$}{0.10} 	imes 100 = 4.2\%$$

Question 13

Which of the following statements about polyprotic acids is correct?

Accepted Answer

The first dissociation constant $$K_{a1} is $$always greater than the second $$K_{a2}.$$

Question 14

Which of the following best explains why the equilibrium for the reaction $$CH_3COOH(aq) + H_2O(l) \rightleftharpoons H_3O^+(aq) + CH_3COO^-(aq)$$ lies to the left?

Accepted Answer

Acetate ion ($$CH_3COO^-) is a $$stronger base than water.

Question 15

A solution is prepared by dissolving sodium fluoride ($$NaF) in $$water. Given that $$K_a$$ for HF is $$7.2 	imes 10$$^{-4}$$, what is the expected pH of the solution?

Accepted Answer

Greater than 7, because $$F^-$$ acts as a weak base.

Question 16

Which of the following is a correct expression for the acid dissociation constant $$K_a$$ for a generic weak acid $$HA$$?

Accepted Answer

$$K_a = \frac{[H_3O^+][A^-]}{[HA]}$$

Question 17

If the pH of rainwater is 5.60, what is the hydronium ion concentration?

Accepted Answer

$$[H_3O^+] = 10$$^{-5.60}$$ = 2.5 	imes 10$$^{-6}$$\ M$$

Question 18

Which of the following best describes the acid-base properties of a solution of $$NH_4Cl$$?

Accepted Answer

The solution will be acidic because $$NH_4$$^+$$ is a weak acid.

Acid-Base Equilibria: General Chemistry Study Notes

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