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Leaving Cert Chemistry: The mole

How often The mole 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.

The mole, Higher Level(8 marks)

Quick ones on The mole.

(a)Value of Avogadro's constant?
  1. 6.022 x 10^22
  2. 6.022 x 10^23
  3. 3.011 x 10^23
(b)Number of molecules in 0.5 mol of a gas?
  1. 1.204 x 10^24
  2. 6.022 x 10^23
  3. 3.011 x 10^23
(c)Number of moles in 8.0 g of methane, CH4 (M = 16)?
  1. 0.5 mol
  2. 0.8 mol
  3. 2 mol
Show the answers

(a) 6.022 x 10^23

(b) 3.011 x 10^23

(c) 0.5 mol

Your turn: Higher Level questions on The mole.

Higher Level

Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q1, Q4(i), Q10(c)
2025Q10(c)
2024Q4(k), Q10(c)
2023Q4(k), Q10(b)
2022Q4(f), Q4(k), Q10(c)
2021Q10(c)
2019Q4(i), Q10(c)
2018Q10(c)
2017Q11(a)
2016Q4(g), Q11(a)

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

More The mole questions

The mole, 3 marks

When finding the Mr of a volatile liquid, why is there a pinhole in the foil over the flask?

  1. To let air into the flask as it cools, so the vapour mixes with it evenly
  2. To stop the liquid boiling too fast and splashing out of the flask
  3. So the vapour fills the flask at atmospheric pressure while the excess escapes
Show the answer

So the vapour fills the flask at atmospheric pressure while the excess escapes

The flask ends up full of vapour only, at a known pressure and temperature. Its mass and volume then give n from pV = nRT, and Mr = mass / n.

The mole, 3 marks

Mass of 3.0 x 10^22 molecules of CO2? (M = 44; Avogadro constant 6.0 x 10^23)

  1. 22 g
  2. 2.2 g
  3. 0.22 g
Show the answer

2.2 g

Moles = 3.0 x 10^22 / 6.0 x 10^23 = 0.05 mol. Mass = 0.05 x 44 = 2.2 g.

The mole, 3 marks

0.2 mol of Mg is added to 0.3 mol of HCl. Mg + 2HCl -> MgCl2 + H2. Which reagent is limiting?

  1. Hydrochloric acid
  2. Magnesium
  3. Neither of them
Show the answer

Hydrochloric acid

0.2 mol of Mg would need 0.4 mol of HCl. Only 0.3 mol is present, so the acid runs out first and some magnesium is left.

Ordinary Level

Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q10(c)
2025Q10(c)
2024Q4(a)
2023Q4(f), Q10(c)
2022Q10(c)
2021Q10(c)
2019Q10(c), Q11(b)
2018Q10(c)
2017Q10(c)
2016Q4(g), Q11(b)

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

More The mole questions

The mole, 3 marks

Number of moles in 11 g of carbon dioxide, CO2 (M = 44)?

  1. 4 mol
  2. 484 mol
  3. 0.25 mol
Show the answer

0.25 mol

Moles = mass divided by molar mass = 11 / 44 = 0.25 mol.

The mole, 3 marks

Percentage by mass of calcium in calcium carbonate (Ca = 40, CaCO3 = 100)?

  1. 12%
  2. 40%
  3. 60%
Show the answer

40%

% calcium = 40 / 100 x 100 = 40%.

The mole, 2 marks

Mass of 2 mol of water, H2O (M = 18)?

  1. 36 g
  2. 9 g
  3. 18 g
Show the answer

36 g

Mass = moles x molar mass = 2 x 18 = 36 g.

Other Chemistry topics

All of Leaving Cert Chemistry