Subjects · Leaving Cert Chemistry
Leaving Cert Chemistry: pH
How often pH comes up on the Chemistry papers, every year it was asked, and questions to try.
HL Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker
OL Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker
June 2027 is the first exam on the new Chemistry course. These come from the 2016–2026 papers, so read them as a guide.
Quick ones on pH.
- pH = log10[H+]
- pH = -log10[H+]
- pH = -log10[OH-]
- 12
- 1
- 2
- 1 x 10⁻⁴ mol l⁻¹
- 1 x 10⁻¹⁰ mol l⁻¹
- 4 mol l⁻¹
Show the answers
(a) pH = -log10[H+]
(b) 2
(c) 1 x 10⁻⁴ mol l⁻¹
Higher Level
Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker
Every paper, year by year
| Year | Where it came up |
|---|---|
| 2026 | Q11(c) |
| 2025 | Q7 |
| 2024 | Q9 |
| 2023 | Q7 |
| 2022 | Q9 |
| 2021 | Q4(i), Q7 |
| 2019 | Q7 |
| 2018 | Q11(b) |
| 2017 | Q9 |
| 2016 | Q10(a) |
Links open the State Examinations Commission’s paper for that year.
More pH questions
pH, 2 marks
What is a buffer solution?
- A solution that always keeps a pH of exactly 7, whatever is added to it
- A solution that has been diluted ten times to lower its concentration
- A solution that resists a change in pH when small amounts of acid or base are added
Show the answer
A solution that resists a change in pH when small amounts of acid or base are added
A typical buffer is a weak acid together with its salt, which can mop up added H+ or added OH-.
pH, 3 marks
pH of a 0.10 mol/L weak acid with Ka = 1.0 x 10^-5?
- 5
- 3
- 1
Show the answer
3
[H+] = square root of (Ka x c) = square root of (1.0 x 10^-6) = 1.0 x 10^-3, so pH = 3.
pH, 3 marks
Why is the pH of 0.1 mol/L ethanoic acid higher than that of 0.1 mol/L HCl?
- It is only partly ionised
- It has more hydrogen atoms
- HCl is the weaker acid of the two
Show the answer
It is only partly ionised
Ethanoic acid is weak, so only a small fraction of its molecules release H+. [H+] is lower, so the pH is higher.
Ordinary Level
Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker
Every paper, year by year
| Year | Where it came up |
|---|---|
| 2026 | Q7 |
| 2025 | Q7 |
| 2024 | Q9 |
| 2023 | Q7 |
| 2022 | Q7 |
| 2021 | Q7 |
| 2019 | Q9 |
| 2018 | Q4(e) |
| 2017 | Q11(b) |
| 2016 | Q10(b) |
Links open the State Examinations Commission’s paper for that year.
More pH questions
pH, 2 marks
Colour of universal indicator in a strong acid of pH 1?
- Green
- Purple
- Red
Show the answer
Red
Universal indicator is red in strong acid, green when neutral and purple (violet) in strong alkali.
pH, 2 marks
Instrument that gives an accurate reading of pH?
- A bomb calorimeter
- A pH meter
- A mass spectrometer
Show the answer
A pH meter
A pH meter uses an electrode dipped in the solution. It is more accurate than universal indicator.
pH, 2 marks
A solution has a pH of 10. It is?
- Alkaline
- Acidic
- Neutral
Show the answer
Alkaline
Any pH above 7 is alkaline (basic). Soap solutions and household ammonia are in this range.
Other Chemistry topics
- Acids and bases
- Atomic structure
- Chemical equilibrium
- Concentration
- Covalent bonding
- Electronegativity
- Fuels and heats of reaction
- Functional groups
- Gas laws
- Hydrocarbons
- Mandatory experiments
- Organic reactions
- Oxidation and reduction
- Rates of reaction
- Shapes of molecules
- The mole
- The periodic table
- Trends
- Volumetric analysis
- Water treatment
- Electron configuration
- Formulas and equations
- Organic synthesis
- Radioactivity
- Instrumentation and separation
- Ionic bonding
- Intermolecular forces
- Electrochemistry
- Environmental chemistry
- Isomerism
- Industrial chemistry
- Lab safety
- States of matter