Q: Which of the following best describes the relationship between $$ K_a $$ and $$ K_b $$ for a conjugate acid-base pair at $$ 25~^\circ\mathrm{C} $$?

$$ K_a \times K_b = 1.0 \times 10$$^{-14}$$ $$

Question 1

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

Accepted Answer

A substance that donates a proton

Question 2

Which of the following reactions demonstrates the Arrhenius definition of a base?

Accepted Answer

$$ \mathrm{NH_3$(aq) + H_2O(l) \rightarrow NH_4$^+(aq) + OH^-(aq)} $$

Question 3

Which of the following is a Lewis acid in the reaction $$ \mathrm{BF_3$ + NH_3$ \rightarrow F_3B-NH_3$} $$?

Accepted Answer

$$ \mathrm{BF_3$} $$

Question 4

Which pair represents a conjugate acid-base pair?

Accepted Answer

$$ \mathrm{H_2O} $$ and $$ \mathrm{OH^-} $$

Question 5

What is the pH of a $$ 0.0018~\mathrm{M} $$ KOH solution at $$ 25~^\circ\mathrm{C} $$? (Assume complete dissociation.)

Accepted Answer

$$ 11.26 $$

Question 6

A $$ 0.10~\mathrm{M} $$ solution of a weak acid HA has a $$ K_a = 5.2 	imes 10$$^{-7}$$ . $$What is the percent ionization?

Accepted Answer

$$ 0.23\% $$

Question 7

Which salt will produce a basic solution when dissolved in water?

Accepted Answer

KCN

Question 8

Given $$ K_a $$ for HCN is $$ 4.9 	imes 10$$^{-10}$$ $$ and $$ K_b $$ for NH3 is $$ 1.8 	imes 10$$^{-5}$$ $$, what is $$ K_b $$ for CN⁻?

Accepted Answer

$$ 2.0 	imes 10$$^{-5}$$ $$

Question 9

What is the pH of a $$ 0.20~\mathrm{M} $$ solution of KCN at $$ 25~^\circ\mathrm{C} $$? ($$ K_b $$ for CN⁻ is $$ 2.0 	imes 10$$^{-5}$$ )$$

Accepted Answer

$$ 11.30 $$

Question 10

Which of the following best explains why the percent ionization of a weak acid increases as its concentration decreases?

Accepted Answer

Dilution shifts the equilibrium to favor more ionization

Question 11

A solution of $$ 0.25~\mathrm{M}  K$_3PO$_4 is $$prepared. What is the pH of the solution? ($$ K_b $$ for PO$$_4$$^{3-}$$ is  2.38$$ 	imes $$10^{-2}$$ $$)

Accepted Answer

$$ 12.82 $$

Question 12

Which of the following statements about indicators is correct?

Accepted Answer

Indicators are weak acids that change color over a range of pH values

Question 13

What is the $$ pK_a  of an $$indicator that changes color from pH 6.4 to 8.0?

Accepted Answer

$$ 7.2 $$

Question 14

Which of the following amines is the strongest base?

Accepted Answer

$$ \mathrm{CH_3NH_2} $$

Question 15

A $$ 0.365~\mathrm{M} $$ ammonia solution ($$ K_b = 1.8 	imes 10$$^{-5}$$ ) $$has what percent ionization?

Accepted Answer

$$ 0.70\% $$

Question 16

Which of the following best describes the relationship between $$ K_a $$ and $$ K_b $$ for a conjugate acid-base pair at $$ 25~^\circ\mathrm{C} $$?

Accepted Answer

$$ K_a 	imes K_b = 1.0 	imes 10$$^{-14}$$ $$

Question 17

Which of the following solutions is most acidic at $$ 25~^\circ\mathrm{C} $$?

Accepted Answer

$$ 0.0023~\mathrm{M}~\mathrm{HCl} $$

Question 18

Which of the following is the correct $$ K_b $$ expression for the reaction $$ \mathrm{CH_3CH_2NH_2(aq) + H_2O(l) \rightleftharpoons CH_3CH_2NH_3^+(aq) + OH^-(aq)} $$?

Accepted Answer

$$ \frac{[CH_3CH_2NH_3^+][OH^-]}{[CH_3CH_2NH_2]} $$

Question 19

Aspirin (acetylsalicylic acid, $$ C_9H_8O_4 ) is a $$weak monoprotic acid. If $$ 2.00~\mathrm{g}  is $$dissolved in $$ 0.600~\mathrm{L}  of $$water and the pH is $$ 2.61 $$, what is the $$ K_a $$?

Accepted Answer

$$ 3.8 	imes 10$$^{-4}$$ $$

Acid-Base Indicators and pH Color Changes

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