$H_2S$; $K_a = 9.1 \times 10^{-8}$; weak acid

The concentration of $[H^+]$ and $[OH^-]$ are both $1.0 \times 10^{-7}$ M at 25°C

$\frac{[H_3O^+]}{[HA]_{initial}} \times 100\%$

Question 1

Which of the following best describes a Lewis acid?

Accepted Answer

A substance that accepts an electron pair

Question 2

Which of the following reactions is classified as a Brønsted-Lowry acid-base reaction?

Accepted Answer

$NH_3 + H_2O \rightarrow NH_4^+ + OH^-$

Question 3

Which factor most strongly increases the strength of a binary acid $HX$?

Accepted Answer

A longer and weaker $H-X$ bond

Question 4

Given the acids $HClO_4$, $HClO_3$, and $HClO$, which is the strongest acid?

Accepted Answer

$HClO_4$

Question 5

What is the $pH$ of a solution with $[H_3O^+] = 1.7 	imes 10^{-4}$ M?

Accepted Answer

$pH = 3.77$

Question 6

Which of the following is true about strong acids?

Accepted Answer

They completely ionize in water

Question 7

If the $K_a$ for $HA$ is $1.8 	imes 10^{-5}$ and the initial concentration is $0.10$ M, what is the $[H_3O^+]$ at equilibrium? (Assume $x$ is small)

Accepted Answer

$1.3 	imes 10^{-3}$ M

Question 8

Which of the following pairs correctly matches the acid with its $K_a$ value and relative strength?

Accepted Answer

$H_2S$; $K_a = 9.1 	imes 10^{-8}$; weak acid

Question 9

Which of the following statements about the self-ionization of water is correct?

Accepted Answer

The concentration of $[H^+]$ and $[OH^-]$ are both $1.0 	imes 10^{-7}$ M at 25°C

Question 10

Which of the following is the correct formula for calculating percent ionization of a weak acid?

Accepted Answer

$\frac{[H_3O^+]}{[HA]_{initial}} 	imes 100\%$

Question 11

Which of the following best explains why $HCl$ is a stronger acid than $HF$?

Accepted Answer

$H-Cl$ bond is longer and weaker than $H-F$

Question 12

A solution has $[OH^-] = 2.0 	imes 10^{-3}$ M at 25°C. What is its $pOH$?

Accepted Answer

$pOH = 2.70$

Question 13

Which of the following is NOT a characteristic of a weak base?

Accepted Answer

Complete ionization in water

Question 14

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

Accepted Answer

$NaCHO_2$

Question 15

What is the $[H_3O^+]$ in a solution with $pH = 4.80$?

Accepted Answer

$1.6 	imes 10^{-5}$ M

Question 16

Which of the following is the correct equilibrium expression for the ionization of a weak acid $HA$?

Accepted Answer

$K_a = \frac{[H_3O^+][A^-]}{[HA]}$

Question 17

Which of the following is a correct statement about polyprotic acids?

Accepted Answer

Each ionization step has its own $K_a$

Question 18

Which of the following is the strongest acid among the following hydrides: $H_2O$, $H_2S$, $H_2Se$?

Accepted Answer

$H_2Se$

Question 19

A solution of $0.115$ M $HA$ has a $pH$ of $3.29$. What is the acid ionization constant $K_a$ for $HA$?

Accepted Answer

$K_a = 1.6 	imes 10^{-4}$

Acids and Bases: Models, Strength, and Calculations

Study Guide - Practice Questions