Question 1

Which of the following statements best describes the relationship between $K_a$ and acid strength?

Accepted Answer

A higher $K_a$ value indicates a stronger acid.

Question 2

Given the following acids and their $K_a$ values at 25°C, which is the strongest acid?

$\mathrm{HCN},\ K_a = 4.9 	imes 10^{-10}$

$\mathrm{HIO},\ K_a = 2.0 	imes 10^{-11}$

$\mathrm{HNO_2},\ K_a = 4.6 	imes 10^{-4}$

$\mathrm{HClO_2},\ K_a = 1.1 	imes 10^{-2}$

Accepted Answer

$\mathrm{HClO_2}$

Question 3

Which of the following correctly expresses 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 4

A student is given a solution of a weak acid with $K_a = 1.3 	imes 10^{-3}$. What is the $pK_a$ of this acid?

Accepted Answer

$pK_a = 2.89$

Question 5

Which of the following bases is the strongest, given their $K_b$ values?

A) $K_b = 1.8 	imes 10^{-5}$

B) $K_b = 4.2 	imes 10^{-7}$

C) $K_b = 6.3 	imes 10^{-10}$

D) $K_b = 2.5 	imes 10^{-6}$

Accepted Answer

A

Question 6

Aspirin (acetylsalicylic acid) has $K_a = 3.3 	imes 10^{-4}$. Calculate its $pK_a$ value.

Accepted Answer

$pK_a = 3.48$

Question 7

If the $pK_a$ of an acid is 4.75, what is the $K_a$ value?

Accepted Answer

$K_a = 1.8 	imes 10^{-5}$

Question 8

Which of the following statements is true regarding the relationship between $pK_a$ and acid strength?

Accepted Answer

A lower $pK_a$ value indicates a stronger acid.

Question 9

A weak base has a $K_b$ of $1.8 	imes 10^{-5}$. What is its $pK_b$?

Accepted Answer

$pK_b = 4.74$

Question 10

If $K_w = 1.0 	imes 10^{-14}$ at 25°C, and the $K_a$ of a weak acid is $1.8 	imes 10^{-5}$, what is the $K_b$ of its conjugate base?

Accepted Answer

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

Question 11

Which of the following is the weakest conjugate base?

A) $K_a = 1.8 	imes 10^{-5}$

B) $K_a = 4.2 	imes 10^{-7}$

C) $K_a = 6.3 	imes 10^{-10}$

D) $K_a = 2.5 	imes 10^{-6}$

Accepted Answer

C

Question 12

A solution contains $NH_3$ ($K_b = 1.8 	imes 10^{-5}$) and $CH_3COOH$ ($K_a = 1.8 	imes 10^{-5}$). Which statement is correct?

Accepted Answer

Both are equally strong in water.

Question 13

Which of the following is the correct formula for calculating $pK_a$?

Accepted Answer

$pK_a = -\log K_a$

Question 14

A medication has a $pK_a$ of 3.5. Is it a stronger or weaker acid than one with a $pK_a$ of 4.5?

Accepted Answer

It is a stronger acid.

Question 15

Which of the following is the correct relationship between $pK_a$ and $pK_b$ for a conjugate acid-base pair at 25°C?

Accepted Answer

$pK_a + pK_b = 14$

Question 16

Which of the following acids is the weakest?

A) $K_a = 1.8 	imes 10^{-5}$

B) $K_a = 4.2 	imes 10^{-7}$

C) $K_a = 6.3 	imes 10^{-10}$

D) $K_a = 2.5 	imes 10^{-6}$

Accepted Answer

C

Question 17

A buffer solution is made from a weak acid with $K_a = 1.8 	imes 10^{-5}$ and its conjugate base. What is the $pK_a$ of the acid?

Accepted Answer

$pK_a = 4.74$

Question 18

If $K_a$ for a weak acid is $2.5 	imes 10^{-6}$, what is the $pK_a$?

Accepted Answer

$pK_a = 5.60$

Question 19

Which of the following is true about the $K_a$ and $K_b$ values for a conjugate acid-base pair?

Accepted Answer

If $K_a$ is large, $K_b$ is small.

Question 20

A solution contains $NH_4^+$ ($K_a = 5.6 	imes 10^{-10}$). What is the $K_b$ of $NH_3$?

Accepted Answer

$K_b = 1.8 	imes 10^{-5}$

Acid-Base Equilibria: Ka, Kb, pKa, and pKb

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