Q: Calculate the pH of a 0.25 mol/L solution of HNO3(aq) at SATP.

$$\text{pH} = -\log(0.25) = 0.60$$

Q: A 0.10 mol/L solution of ethanoic acid, HC2H3O2(aq), is found to be 1.3% ionized. What is the concentration of $$\mathrm{H^+}$$ ions in the solution?

$$[\mathrm{H^+}] = 1.3 \times 10$$^{-3}$$~\mathrm{mol/L}$$

Q: Which of the following is the correct expression for the percentage ionization of a weak acid, HA, in water?

$$\text{percentage ionization} = \frac{[\mathrm{H^+}]}{[\mathrm{HA}]_{\text{initial}}} \times 100\%$$

Q: A 0.25 mol/L solution of HNO3(aq) is prepared. What is the concentration of $$[\mathrm{OH^-}] in $$the solution at SATP? ($$K_w = 1.0 \times 10$$^{-14}$$)

$$[\mathrm{OH^-}] = 4.0 \times 10$$^{-14}$$~\mathrm{mol/L}$$

Q: A 0.10 mol/L solution of nitrous acid, HNO2(aq), has a pH of 2.2. What is the $$[\mathrm{H^+}] in $$the solution?

$$[\mathrm{H^+}] = 6.3 \times 10$$^{-3}$$~\mathrm{mol/L}$$

Question 1

A scientist prepares a 1.0 mol/L solution of HCl(aq). Which of the following statements best describes the major entities present in the solution?

Accepted Answer

Mostly H1(aq) and Cl2(aq) ions, with virtually no HCl(aq) molecules.

Question 2

Calculate the pH of a 0.25 mol/L solution of HNO3(aq) at SATP.

Accepted Answer

$$	ext{pH} = -\log(0.25) = 0.60$$

Question 3

A 0.10 mol/L solution of ethanoic acid, HC2H3O2(aq), is found to be 1.3% ionized. What is the concentration of $$\mathrm{H^+}$$ ions in the solution?

Accepted Answer

$$[\mathrm{H^+}] = 1.3 	imes 10$$^{-3}$$~\mathrm{mol/L}$$

Question 4

Which of the following best explains why the autoionization of water can be ignored when calculating the pH of a strong acid solution?

Accepted Answer

The concentration of $$\mathrm{H^+}$$ from the acid is much greater than that from water.

Question 5

A 0.100 mol/L solution of hydrofluoric acid, HF(aq), has a percentage ionization of 7.8%. Calculate the acid ionization constant, $$K_a$$, for HF.

Accepted Answer

$$K_a = 6.6 	imes 10$$^{-4}$$

Question 6

Which of the following is the correct expression for the percentage ionization of a weak acid, HA, in water?

Accepted Answer

$$	ext{percentage ionization} = \frac{[\mathrm{H^+}]}{[\mathrm{HA}]_{	ext{initial}}} 	imes 100\%$$

Question 7

A 0.10 mol/L solution of methanoic acid, HCHO2(aq), has a pH of 2.38. What is the percentage ionization of the acid?

Accepted Answer

$$4.2\%$$

Question 8

Which of the following best describes the ionization of sulfuric acid, $$\mathrm{H_2SO_4}$$, in water?

Accepted Answer

The first ionization is strong and the second is weak.

Question 9

Calculate the pH of a 0.10 mol/L solution of ascorbic acid, $$\mathrm{H_2C_6H_6O_6}$$, given $$K_{a1} = 7.9 	imes 10$$^{-5}$$ and K$$_{a2} = 1.6 	imes $$10^{-12}.$$

Accepted Answer

$$	ext{pH} \approx 2.55$$

Question 10

A solution of hypochlorous acid, HClO(aq), has a concentration of 0.100 mol/L and a pH of 4.23. What is the value of $$K_a$$ for hypochlorous acid?

Accepted Answer

$$K_a = 3.5 	imes 10$$^{-8}$$

Question 11

Which of the following best explains why only the first ionization step is usually considered when calculating the pH of a polyprotic acid solution?

Accepted Answer

The first ionization constant ($$K_{a1}) is $$much larger than subsequent ones, so later steps contribute negligibly to $$[\mathrm{H^+}].$$

Question 12

A 0.25 mol/L solution of HNO3(aq) is prepared. What is the concentration of $$[\mathrm{OH^-}] in $$the solution at SATP? ($$K_w = 1.0 	imes 10$$^{-14}$$)

Accepted Answer

$$[\mathrm{OH^-}] = 4.0 	imes 10$$^{-14}$$~\mathrm{mol/L}$$

Question 13

Which of the following is a correct step in solving for the pH of a weak acid solution using an ICE table?

Accepted Answer

Assume $$[\mathrm{H^+}] = x$$ and set up the equilibrium expression using $$K_a.$$

Question 14

A 0.10 mol/L solution of nitrous acid, HNO2(aq), has a pH of 2.2. What is the $$[\mathrm{H^+}] in $$the solution?

Accepted Answer

$$[\mathrm{H^+}] = 6.3 	imes 10$$^{-3}$$~\mathrm{mol/L}$$

Question 15

Which of the following acids is diprotic?

Accepted Answer

Sulfuric acid, $$\mathrm{H_2SO_4}$$

Question 16

A solution of benzoic acid, $$\mathrm{HC_7H_5O_2}$$, has a concentration of $$8.3 	imes 10$$^{-3}$$ mol/L and a pH of 3.14. What is the K_a$ value for benzoic acid?

Accepted Answer

$$K_a = 6.6 	imes 10$$^{-5}$$

Question 17

Which of the following best describes the effect of adding a strong acid to water on the autoionization equilibrium of water?

Accepted Answer

The equilibrium shifts left, decreasing $$[\mathrm{OH^-}].$$

Lesson 8.4: Acid–Base Equilibrium: Calculations Involving Acidic Solutions

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