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Leaving Cert Physics & Chemistry: Hydrogen, oxygen & their compounds

How often Hydrogen, oxygen & their compounds 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

Hydrogen, oxygen & their compounds, Higher Level(8 marks)

Quick ones on Hydrogen, oxygen & their compounds.

(a)When oxygen is made from hydrogen peroxide, what is the role of manganese dioxide?
  1. Reactant that is used up
  2. Catalyst
  3. Drying agent
(b)Balanced equation for the decomposition of hydrogen peroxide?
  1. 2H2O2 → 2H2 + 2O2
  2. H2O2 → H2 + O2
  3. 2H2O2 → 2H2O + O2
(c)Sulfur dioxide is collected by upward displacement of air because it is…
  1. Denser than air and soluble in water
  2. Denser than air and insoluble in water
  3. Less dense than air and soluble in water
Show the answers

(a) Catalyst

(b) 2H2O2 → 2H2O + O2

(c) Denser than air and soluble in water

Your turn: Higher Level questions on Hydrogen, oxygen & their compounds.

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(j), Q12(c)
2024Q7(l)
2023Q7(m)
2022Q7(i), Q7(j)
2021Q7(j), Q7(l)
2019Q7(j), Q12(a)
2018Q7(f), Q7(i)
2017Q12(a)
2016Q7(h)

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

More Hydrogen, oxygen & their compounds questions

Hydrogen, oxygen & their compounds, 3 marks

Why is carbon dioxide used to put out some fires?

  1. It is a good fuel that burns off the other fuel
  2. It reacts with the fuel to cool it below ignition
  3. It is denser than air and does not support burning
Show the answer

It is denser than air and does not support burning

CO2 sinks over the fire like a blanket, keeping out oxygen, and it does not burn or help burning. It leaves no residue, so it suits electrical fires.

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
2025Q12(a)
2024Q7(j), Q12(a), Q12(c)
2023Q7(n), Q9, Q12(a)
2022Q7(n), Q12(a)
2021Q7(n), Q9, Q12(a)
2019Q12(b)
2018Q12(b), Q12(c)
2017Q7(j), Q12(b), Q12(c)
2016Q7(g), Q12(b), Q12(c)

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

More Hydrogen, oxygen & their compounds questions

Hydrogen, oxygen & their compounds, 2 marks

In the lab preparation of oxygen from hydrogen peroxide, manganese dioxide acts as?

  1. An acid
  2. A drying agent
  3. A catalyst
Show the answer

A catalyst

MnO2 speeds up the breakdown of H2O2 and is not used up. It can be filtered out, dried and weighed afterwards: same mass.

Hydrogen, oxygen & their compounds, 2 marks

A catalyst is a substance that?

  1. Is always formed as a product of the reaction
  2. Speeds up a reaction without being used up
  3. Is used up as it starts the reaction off
Show the answer

Speeds up a reaction without being used up

A catalyst gives the reaction an easier route. It is left chemically unchanged at the end, so a small amount can be used again and again.

Hydrogen, oxygen & their compounds, 2 marks

Test for oxygen gas?

  1. It relights a glowing splint
  2. It turns limewater milky
  3. It burns with a squeaky pop
Show the answer

It relights a glowing splint

Oxygen supports combustion strongly. Limewater turning milky is the test for carbon dioxide; a squeaky pop is the test for hydrogen.

Other Physics & Chemistry topics

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