Question 1

Which of the following best describes a Brønsted acid?

Accepted Answer

A species that donates a proton ($$\mathrm{H^+}) to $$another species.

Question 2

Which of the following is a strong base in aqueous solution?

Accepted Answer

NaOH

Question 3

A solution has $$[\mathrm{H^+}] = 1 	imes 10$$^{-4}$$\ \mathrm{M}. $$What is its pH?

Accepted Answer

$$\mathrm{pH} = 4$$

Question 4

Which equation correctly relates pH and pOH in aqueous solution at 25°C?

Accepted Answer

$$\mathrm{pH} + \mathrm{pOH} = 14$$

Question 5

Calculate the pH of a solution prepared by dissolving 10 g of NaOH (molar mass = 40 g/mol) in 600 mL of water. Assume complete dissociation.

Accepted Answer

$$\mathrm{pH} \approx 14$$

Question 6

Which of the following statements about weak acids is correct?

Accepted Answer

Weak acids only partially dissociate in water, resulting in an equilibrium between the acid and its ions.

Question 7

Given a 0.02 M solution of nitrous acid ($$\mathrm{$$HNO_2$$}) $$with $$pK_a = 3.35$$, which formula would you use to approximate the pH?

Accepted Answer

$$\mathrm{pH} = \frac{1}{2} pK_a - \frac{1}{2} \log [\mathrm{HA}]_0$$

Question 8

Which of the following best explains why buffers are effective only within 2 pH units of their $$pK_a$$?

Accepted Answer

Within 2 pH units of $$pK_a$$, both the acid and its conjugate base are present in significant amounts to neutralize added acid or base.

Question 9

A buffer solution is prepared by mixing equal concentrations of a weak acid and its conjugate base. What is the pH of the buffer relative to the $$pK_a of $$the acid?

Accepted Answer

The pH is equal to the $$pK_a of $$the acid.

Question 10

Which of the following equations is the Henderson-Hasselbalch equation for a buffer made from a weak acid and its conjugate base?

Accepted Answer

$$\mathrm{pH} = pK_a + \log \left( \frac{[A^-]}{[HA]} \right)$$

Question 11

A solution is made by mixing 100 mL of 0.5 M $$\mathrm{Mg(OH)_2}$$ with 400 mL of 1.0 M HCl. What is the resulting pH? (Assume complete dissociation and that $$\mathrm{Mg(OH)_2}$$ provides 2 moles of $$\mathrm{OH^-}$$ per mole.)

Accepted Answer

The solution is acidic with $$\mathrm{pH} \u003c 7$$

Question 12

Which of the following best describes the relationship between the strength of an acid and its conjugate base?

Accepted Answer

The stronger the acid, the weaker its conjugate base.

Question 13

Which of the following is the correct expression for the acid dissociation constant ($$K_a) of a $$weak acid $$HA in $$water?

Accepted Answer

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

Question 14

A buffer solution is made by adding 0.1 mol of acetic acid ($$pK_a = 4.76) $$and 0.1 mol of sodium acetate to 1 L of water. What is the pH of the solution?

Accepted Answer

$$\mathrm{pH} = 4.76$$

Question 15

Which of the following best explains why blood is carefully buffered between pH 7.35 and 7.45?

Accepted Answer

To maintain homeostasis and prevent harmful changes in enzyme activity and cellular function.

Question 16

Which of the following is true about the logarithmic nature of the pH scale?

Accepted Answer

A decrease of 1 pH unit corresponds to a tenfold increase in $$[H^+]$$ concentration.

Question 17

A pH meter is used to measure the pH of two juices: orange juice (pH 3.80) and lemon juice (pH 2.57). Which statement is correct?

Accepted Answer

Lemon juice has a higher concentration of $$[H_3O^+]$$ than orange juice.

Question 18

Which of the following best describes the effect of adding a small amount of strong acid to a buffer solution?

Accepted Answer

The pH changes only slightly because the buffer neutralizes the added acid.

Acids, Bases, and Buffers: Principles and Calculations

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