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Leaving Cert Physics & Chemistry: Acids, bases & pH

How often Acids, bases & pH comes up on the Physics & Chemistry papers, every year it was asked, and questions to try.

HL Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

OL Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Acids, bases & pH, Higher Level(8 marks)

Quick ones on Acids, bases & pH.

(a)According to Brønsted–Lowry theory, an acid is a…
  1. Proton acceptor
  2. Proton donor
  3. Hydroxide ion donor
(b)pH of 0.001 M hydrochloric acid?
  1. 11
  2. 0.001
  3. 3
(c)pH of 0.1 M KOH solution?
  1. 13
  2. 7
  3. 1
Show the answers

(a) Proton donor

(b) 3

(c) 13

Your turn: Higher Level questions on Acids, bases & pH.

Higher Level

Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q7(o), Q9, Q12(c)
2024Q7(n), Q9
2023Q7(h), Q12(d)
2022Q9, Q12(d)
2021Q9
2019Q9
2018Q9, Q12(b)
2017Q7(h), Q9
2016Q9, Q12(b)

Links open the State Examinations Commission’s paper for that year.

More Acids, bases & pH questions

Acids, bases & pH, 2 marks

An acid neutralises a base. The products are…

  1. A salt and hydrogen
  2. Water only
  3. A salt and water
Show the answer

A salt and water

Acid + base → salt + water, for example HCl + NaOH → NaCl + H2O. The H+ and OH- ions combine to form water. Hydrogen gas comes from acid + metal.

Acids, bases & pH, 3 marks

A solution has a pH of 4. Its hydrogen ion concentration?

  1. 1 × 10⁴ mol L⁻¹
  2. 1 × 10⁻⁴ mol L⁻¹
  3. 4 mol L⁻¹
Show the answer

1 × 10⁻⁴ mol L⁻¹

pH = −log₁₀[H+], so [H+] = 10 to the power of −pH = 1 × 10⁻⁴ mol L⁻¹. Each pH step is a tenfold change in [H+].

Acids, bases & pH, 2 marks

Colour of phenolphthalein in a basic (alkaline) solution?

  1. Pink
  2. Colourless
  3. Yellow
Show the answer

Pink

Phenolphthalein is colourless in acid and pink in base. It suits titrations of a weak acid with a strong base.

Ordinary Level

Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q7(j), Q7(l), Q9
2024Q7(m), Q9
2023Q9
2022Q9
2021Q9
2019Q7(m), Q9
2018Q9
2017Q7(f), Q9
2016Q9

Links open the State Examinations Commission’s paper for that year.

More Acids, bases & pH questions

Acids, bases & pH, 2 marks

A Brønsted–Lowry acid is a?

  1. Proton acceptor
  2. Electron donor
  3. Proton donor
Show the answer

Proton donor

An acid gives away H+ ions (protons). A base accepts them. HCl donates a proton to water to make H3O+.

Acids, bases & pH, 2 marks

pH is defined as?

  1. -log10[OH-]
  2. -log10[H+]
  3. log10[H+]
Show the answer

-log10[H+]

pH is minus the log to base 10 of the hydrogen ion concentration in mol/L. -log10[OH-] gives pOH, and pH + pOH = 14.

Acids, bases & pH, 3 marks

pH of 0.1 M sodium hydroxide?

  1. 13
  2. 1
  3. 0.1
Show the answer

13

NaOH is a strong base: [OH-] = 0.1 M, so pOH = 1. pH = 14 − 1 = 13. A pH of 1 would be a strong acid.

Other Physics & Chemistry topics

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