Q: Given the acid dissociation constant $$K_a$$ for acetic acid ($$CH_3COOH) is$$ $$1.8 \times 10$$^{-5}$$, what is the base dissociation constant K_b$ for its conjugate base (CH_3$$COO^-$$)? Use K_w = 1.0$$ \times $$10^{-14}.$$

$$K_b = 5.6 \times 10$$^{-10}$$

Question 1

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

Accepted Answer

NaCH3COO

Question 2

Given the acid dissociation constant $$K_a$$ for acetic acid ($$CH_3COOH) is$$ $$1.8 	imes 10$$^{-5}$$, what is the base dissociation constant K_b$ for its conjugate base (CH_3$$COO^-$$)? Use K_w = 1.0$$ 	imes $$10^{-14}.$$

Accepted Answer

$$K_b = 5.6 	imes 10$$^{-10}$$

Question 3

Which of the following statements best explains why $$HF is a $$weak acid in water, while $$HCl$$, $$HBr$$, and $$HI$$ are strong acids?

Accepted Answer

The H-F bond is much stronger than the H-Cl, H-Br, and H-I bonds.

Question 4

Which species is most concentrated in a $$0.10\ \mathrm{M}$$ solution of $$H_2CO_3 ($$carbonic acid)?

Accepted Answer

$$H_2CO_3$$

Question 5

For the diprotic acid $$H_2CO_3$$, which equilibrium reaction occurs first when dissolved in water?

Accepted Answer

$$H_2CO_3 + H_2O \rightleftharpoons $$HCO_3$$^- + H_3O^+$$

Question 6

Calculate the pH of a $$0.25\ \mathrm{M}$$ solution of sodium acetate ($$NaCH_3COO$$). ($$K_a$$ for acetic acid $$= 1.8 	imes 10$$^{-5}$$)

Accepted Answer

pH $$\approx 8.9$$

Question 7

Which of the following best describes why $$HClO_4 is a $$much stronger acid than $$HClO$$?

Accepted Answer

$$HClO_4$$ has more oxygen atoms, which increase the polarity of the O-H bond.

Question 8

Given $$K_a$$ for $$HCN is$$ $$6.2 	imes 10$$^{-10}$$, what is the K_b$ for CN$$^-$$?

Accepted Answer

$$K_b = 1.6 	imes 10$$^{-5}$$

Question 9

Which of the following is true about the successive ionization constants ($$K_{a1}$$, $$K_{a2}$$, $$K_{a3}) $$for polyprotic acids?

Accepted Answer

$$K_{a1} \u003e K_{a2} \u003e K_{a3}$$

Question 10

Which of the following best explains why $$H_2SO_4 is a $$strong acid for its first proton but weak for its second?

Accepted Answer

The first ionization is complete, but the second proton is less easily removed due to increased negative charge.

Question 11

Which of the following best describes the relationship between $$K_a$$, $$K_b$$, and $$K_w$$ for a conjugate acid-base pair?

Accepted Answer

$$K_a 	imes K_b = K_w$$

Question 12

Which of the following is the correct equilibrium expression for the second dissociation of phosphoric acid ($$H_3PO_4$$)?

Accepted Answer

$$K_{a2} = \frac{[H_3O^+][$$HPO_4$$^{2-}]}{[H_2PO_4^-] }$$

Question 13

Which of the following best explains why $$HClO_3 is a $$stronger acid than $$HClO_2$$?

Accepted Answer

$$HClO_3$$ has more oxygen atoms, increasing the electron-withdrawing effect.

Question 14

Which of the following best describes the effect of increasing the electronegativity of the central atom Y in an oxyacid ($$HOY) on $$acid strength?

Accepted Answer

Acid strength increases as electronegativity increases.

Question 15

A $$0.75\ \mathrm{M}$$ solution of $$NaCN is $$prepared. Given $$K_a$$ for $$HCN is$$ $$6.2 	imes 10$$^{-10}$$, what is the expected pH of the solution?

Accepted Answer

pH $$\approx 11.2$$

Question 16

Which of the following best describes a conjugate acid-base pair?

Accepted Answer

Two species that differ by one proton ($$H^+)$$

Question 17

Which of the following is a correct statement about the concentration of species in a $$0.10\ \mathrm{M}$$ solution of $$Na_2CO_3$$?

Accepted Answer

$$CO_3$$^{2-}$$ is the most concentrated species.

Question 18

Which of the following best explains why $$H_2S is a $$much weaker acid than $$H_2SO_4$$?

Accepted Answer

$$H_2SO_4$$ has more oxygen atoms, which stabilize the negative charge after deprotonation.

Acid-Base Equilibria, Conjugate Pairs, and Polyprotic Acids

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