$$\text{pH} = -\log_{10}[H^+]$$

$$1 \times 10$$^{-7}$$ \ \text{mol dm}^{-3}$$

$$[H^+] = 10$$^{-\text{pH}$$}$$

Question 1

Which of the following best describes a Brønsted-Lowry acid?

Accepted Answer

A substance that donates a proton.

Question 2

What is the pH of a solution with $$[H^+] = 1 	imes 10$$^{-4}$$ \ 	ext{mol dm}^{-3}$$?

Accepted Answer

$$4$$

Question 3

A weak acid is best defined as:

Accepted Answer

An acid that only slightly dissociates in solution.

Question 4

Which equation correctly relates pH and hydrogen ion concentration?

Accepted Answer

$$	ext{pH} = -\log_{10}[H^+]$$

Question 5

At 25°C, the ionic product of water ($$K_w) is$$ $$1 	imes 10$$^{-14}$$. What is the $$[OH^-]$$ in pure water at this temperature?

Accepted Answer

$$1 	imes 10$$^{-7}$$ \ 	ext{mol dm}^{-3}$$

Question 6

If the temperature of water increases, what happens to the pH and why?

Accepted Answer

pH decreases because $$K_w$$ increases and more $$H^+$$ ions are produced.

Question 7

Given the equilibrium $$HA \rightleftharpoons H^+ + A^-$$, what is the expression for the acid dissociation constant $$K_a$$?

Accepted Answer

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

Question 8

A buffer solution is best described as:

Accepted Answer

A solution that resists changes in pH when small amounts of acid or base are added.

Question 9

Which indicator would be most suitable for a titration with a neutralisation point at pH 9?

Accepted Answer

Phenolphthalein

Question 10

During a titration of a strong acid with a strong base, what is the expected pH at the equivalence point?

Accepted Answer

pH = 7

Question 11

If $$K_a$$ for a weak acid is $$1 	imes 10$$^{-5}$$, what is the pK_a$?

Accepted Answer

$$5$$

Question 12

Which of the following best explains why buffer solutions are important in biological systems?

Accepted Answer

They maintain a constant pH, which is necessary for enzyme activity.

Question 13

A buffer is made by mixing ethanoic acid and sodium ethanoate. What happens when a small amount of HCl is added?

Accepted Answer

The ethanoate ions react with the added $$H^+ to $$form ethanoic acid, minimising pH change.

Question 14

Which of the following is the correct relationship for calculating $$[H^+]$$ from pH?

Accepted Answer

$$[H^+] = 10$$^{-	ext{pH}$$}$$

Question 15

Which of the following best describes the effect of adding a small amount of $$OH^- to a $$buffer solution?

Accepted Answer

The acid in the buffer reacts with $$OH^-$$, so the pH increases only slightly.

Question 16

A student adds 0.01 mol of NaOH to a buffer solution. What is the most likely outcome?

Accepted Answer

The pH will increase only slightly.

Question 17

Which of the following titration curves would you expect for a weak acid and a strong base?

Accepted Answer

A curve with an equivalence point above pH 7.

Question 18

What is the main reason why the forward reaction in the dissociation of water is endothermic?

Accepted Answer

It absorbs heat, so increasing temperature favours the production of $$H^+$$ and $$OH^-$$ ions.

Acids and Bases: AQA Chemistry A-level Study Notes

Study Guide - Practice Questions