Q: A solution has a pOH of 3.0. What is the concentration of hydroxide ions, [OH$$^-$$]?

$$[\mathrm{OH}^-] = 10$$^{-3.0}$$ = 1.0 \times 10$$^{-3}$$\ \mathrm{M}$$

Q: A 0.10 M solution of acetic acid (CH$$_3$$COOH) has a $$K_a = 1.8 \times 10$$^{-5}$$. What is the equilibrium concentration of hydronium ion, [H_3$O$$^+$$]? (Assume x$$ \ll 0.10$$.)

$$[\mathrm{H}_3\mathrm{O}^+] = \sqrt{(1.8 \times 10$$^{-5}$$)(0.10)} = 1.34 \times 10$$^{-3}$$\ \mathrm{M}$$

Q: A 0.35 M solution of HCN contains $$6.25 \times 10$$^{-6}$$ M $$\mathrm{H}_3\mathrm{O}^+$$. What is the percent ionization of HCN?

$$\%\ \mathrm{ionization} = \frac{6.25 \times 10$$^{-6}$$}{0.35} \times 100\% = 0.0018\%$$

Q: A 0.1 M solution of ammonia (NH$$_3) $$has $$K_b = 1.8 \times 10$$^{-5}$$. What is the pH of this solution? (Assume x$$ \ll 0.1$$.)

$$[\mathrm{OH}^-] = \sqrt{(1.8 \times 10$$^{-5}$$)(0.1)} = 1.34 \times 10$$^{-3}$$\ \mathrm{M}$$;\ pOH = -\log(1.34 \times $$10^{-3}) = 2.87$$;\ pH = 14 - 2.87 = 11.13$

Q: Which of the following statements about the autoionization of water is correct?

$$K_w = [\mathrm{H}_3\mathrm{O}^+][\mathrm{OH}^-] = 1.0 \times 10$$^{-14}$$\ at\ 25^\circ\mathrm{C}$

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$$_4 is $$prepared. What is the pH of this 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 3.0. What is the concentration of hydroxide ions, [OH$$^-$$]?

Accepted Answer

$$[\mathrm{OH}^-] = 10$$^{-3.0}$$ = 1.0 	imes 10$$^{-3}$$\ \mathrm{M}$$

Question 5

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

Accepted Answer

NaF

Question 6

A 0.10 M solution of acetic acid (CH$$_3$$COOH) has a $$K_a = 1.8 	imes 10$$^{-5}$$. What is the equilibrium concentration of hydronium ion, [H_3$O$$^+$$]? (Assume x$$ \ll 0.10$$.)

Accepted Answer

$$[\mathrm{H}_3\mathrm{O}^+] = \sqrt{(1.8 	imes 10$$^{-5}$$)(0.10)} = 1.34 	imes 10$$^{-3}$$\ \mathrm{M}$$

Question 7

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

Accepted Answer

The H–F bond is much stronger and less easily broken than the H–Cl bond.

Question 8

A 0.35 M solution of HCN contains $$6.25 	imes 10$$^{-6}$$ M $$\mathrm{H}_3\mathrm{O}^+$$. What is the percent ionization of HCN?

Accepted Answer

$$\%\ \mathrm{ionization} = \frac{6.25 	imes 10$$^{-6}$$}{0.35} 	imes 100\% = 0.0018\%$$

Question 9

Which of the following is a Lewis acid?

Accepted Answer

BF$$_3$$

Question 10

A 0.1 M solution of ammonia (NH$$_3) $$has $$K_b = 1.8 	imes 10$$^{-5}$$. What is the pH of this solution? (Assume x$$ \ll 0.1$$.)

Accepted Answer

$$[\mathrm{OH}^-] = \sqrt{(1.8 	imes 10$$^{-5}$$)(0.1)} = 1.34 	imes 10$$^{-3}$$\ \mathrm{M}$$;\ pOH = -\log(1.34 	imes $$10^{-3}) = 2.87$$;\ pH = 14 - 2.87 = 11.13$

Question 11

Which of the following statements about the autoionization of water is correct?

Accepted Answer

$$K_w = [\mathrm{H}_3\mathrm{O}^+][\mathrm{OH}^-] = 1.0 	imes 10$$^{-14}$$\ at\ 25^\circ\mathrm{C}$

Question 12

Which of the following will result in a neutral solution when dissolved in water?

Accepted Answer

KNO$$_3$$

Question 13

Which of the following acids is the strongest, based on structure and periodic trends?

Accepted Answer

HClO$$_4$$

Question 14

A 0.01 M solution of a weak base has a pOH of 5.0. What is the pH of the solution?

Accepted Answer

$$\mathrm{pH} = 14 - 5.0 = 9.0$$

Question 15

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 16

A 0.10 M solution of a diprotic acid, H$$_2A$$, has $$K_{a1} = 1.0 	imes 10$$^{-3}$$ and K$$_{a2} = 1.0 	imes $$10^{-8}. $$What is the best approach to estimate the pH of this solution?

Accepted Answer

Treat it as a monoprotic acid using only $$K_{a1}$$, since $$K_{a1} \gg K_{a2}.$$

Question 17

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

Accepted Answer

$$K_a 	imes K_b = K_w$$

Question 18

A solution is prepared by mixing 50.0 mL of 0.150 M HBr and 25.0 mL of 0.020 M HCl. What is the pH of the resulting solution? (Assume volumes are additive and both acids are strong.)

Accepted Answer

First, calculate total moles of H$$_3O$^+$$: $$n_{\mathrm{HBr}} = 0.050 	imes 0.150 = 0.0075$$ mol, $$n_{\mathrm{HCl}} = 0.025 	imes 0.020 = 0.0005$$ mol. Total moles = $$0.0080$$ mol. Total volume = $$0.075 L$$. $$[\mathrm{H}_3\mathrm{O}^+] = 0.0080 / 0.075 = 0.107 M$$. $$\mathrm{pH} = -\log(0.107) = 0.97$$

Acid-Base Equilibria: Concepts, Definitions, and Reactions

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