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

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

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}$$) and CH_3$$COOH$$ (K_a = 1.8$$ 	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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