ChemistryICSE Class 8 · Hydrogen

Properties and Uses of Hydrogen, and Oxidation and Reduction (ICSE Class 8 Chemistry)

Updated 17 October 2026 · Fact-checked

Hydrogen is the lightest gas, colourless and odourless, burns with a pale blue flame but does not support combustion, and is a reducing agent. Oxidation is addition of oxygen or removal of hydrogen; reduction is removal of oxygen or addition of hydrogen; both occur together in a redox reaction.

Follow the oxygen: CuO loses it and is reduced, while H₂ gains it to form water and is oxidised, so both happen together.

Illustration drawn for QuestionBuddy.

Understand Properties and Uses of Hydrogen; Oxidation and Reduction

Physical properties. Colourless, odourless, tasteless; the lightest substance known (about 14 times lighter than air); sparingly soluble in water; neutral to litmus.

Chemical properties.

Combustible, does not support combustion: burns in air with a pale blue flame, $2 H_{2} + O_{2} \to 2 H_{2} O$ ; a burning splinter goes out in the gas. Hydrogen mixed with air explodes when lit.
Reducing agent: hot hydrogen takes oxygen from oxides of less reactive metals: $C u O + H_{2} \to C u + H_{2} O$ (black CuO turns reddish brown; water droplets form). It does not reduce oxides of very reactive metals such as Na, Ca, Mg, Al, Zn.
Combines with non-metals: $H_{2} + C l_{2} \to 2 H C l$ ; $N_{2} + 3 H_{2} ⇌ 2 N H_{3}$ ; $H_{2} + S \to H_{2} S$ .
With very reactive metals: $2 N a + H_{2} \to 2 N a H$ .

Uses (each from a property):

Hydrogenation of oils with a nickel catalyst: liquid oil to semi-solid fat.
Making ammonia (Haber's process) for fertilisers.
Fuel: rocket fuel (liquid hydrogen); burns to water only (clean fuel).
Oxy-hydrogen flame (about 2800 °C): welding and cutting.
Extracting metals as a reducing agent.
Once used in balloons (lightest gas); now helium, because hydrogen is highly flammable.

Oxidation and reduction (Class VIII definitions).

	Oxidation	Reduction
Oxygen	addition	removal
Hydrogen	removal	addition

An oxidising agent gives oxygen or removes hydrogen and is itself reduced. A reducing agent removes oxygen or gives hydrogen and is itself oxidised. The two happen together: a redox reaction.

Example: $C u O + H_{2} \to C u + H_{2} O$ : CuO is reduced (oxidising agent); H₂ is oxidised (reducing agent).
Example: $H_{2} S + C l_{2} \to 2 H C l + S$ : H₂S loses hydrogen (oxidised, reducing agent); Cl₂ gains hydrogen (reduced, oxidising agent).

Properties and Uses of Hydrogen; Oxidation and Reduction: formulas and key facts

Burning: $2 H_{2} + O_{2} \to 2 H_{2} O$; 4 g + 32 g gives 36 g.
Reduction of copper oxide: $C u O + H_{2} \to C u + H_{2} O$; CuO reduced; H₂ oxidised.
Redox definitions: Oxidation: gain of oxygen or loss of hydrogen | Reduction: loss of oxygen or gain of hydrogen; Together = redox.
Haber and chlorine: $N_{2} + 3 H_{2} ⇌ 2 N H_{3} H_{2} + C l_{2} \to 2 H C l$; Combination with non-metals.

How to solve Properties and Uses of Hydrogen; Oxidation and Reduction questions

For redox, track oxygen and hydrogen on each reactant and label the agents.

1Find which substance gains oxygen or loses hydrogen: it is oxidised.
2The other loses oxygen or gains hydrogen: it is reduced.
3The oxidised substance is the reducing agent; the reduced substance is the oxidising agent.
4For mass questions use 4 g H₂ : 32 g O₂ : 36 g H₂O.

Properties and Uses of Hydrogen; Oxidation and Reduction in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Margarine from oil

Suppose a factory passes hydrogen through hot vegetable oil in the presence of nickel to make a spread.

Name the process and the role of nickel.

Try it first, then show the solutionSolution

The process is hydrogenation: liquid oil becomes semi-solid fat.
Nickel is the catalyst that speeds up the reaction.

Answer: Hydrogenation with a nickel catalyst.

Memory hook: Hydrogen turns oil to fat.

Balloon safety

Imagine a fair uses balloons filled with hydrogen near a bonfire.

Why is this dangerous and what is used today?

Try it first, then show the solutionSolution

Hydrogen is highly flammable and explodes with air when lit.
Helium, which does not burn, is used instead.

Answer: Hydrogen burns and explodes; helium is safe.

Memory hook: Lightest, but flammable.

Tricks to remember Properties and Uses of Hydrogen; Oxidation and Reduction

Short memory aids. Say each one aloud once, then use it on a question the same day.

Oxygen in, hydrogen out
Oxygen in or hydrogen out means oxidation; oxygen out or hydrogen in means reduction.
Use it when: Definitions.
The oxidised is the reducer
The substance that gets oxidised is the reducing agent.
Use it when: Agents.
Combustible, not a supporter
Hydrogen burns but a splinter goes out in it.
Use it when: Properties.

Properties and Uses of Hydrogen; Oxidation and Reduction: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: A burning splinter · 1 mark · MCQBoard level

A burning splinter is plunged into a jar of hydrogen. It:
(a) burns brighter
(b) goes out and the gas burns at the mouth
(c) explodes inside the jar
(d) is unaffected

Try it first, then show the solutionSolution

Hydrogen burns (at the mouth, with a pale blue flame) but does not support combustion, so the splinter goes out.

Answer: (b)

Example 2: Define redox · 2 marks · Short answerBoard level

Define oxidation and reduction in terms of oxygen and hydrogen, and say what is meant by a redox reaction.

Try it first, then show the solutionSolution

Oxidation: addition of oxygen or removal of hydrogen; reduction: removal of oxygen or addition of hydrogen. (1)
Both occur together in the same reaction, a redox reaction. (1)

Answer: Oxidation and reduction together.

Example 3: Name the agents · 4 marks · Long answerHarder board level

For each reaction identify the substance oxidised, the substance reduced, the oxidising agent and the reducing agent: (a) $P b O + H_{2} \to P b + H_{2} O$ , (b) $2 H_{2} S + O_{2} \to 2 S + 2 H_{2} O$ , (c) $F e_{2} O_{3} + 3 C O \to 2 F e + 3 C O_{2}$ .

Try it first, then show the solutionSolution

(a) Oxidised: H₂ (gains oxygen); reduced: PbO (loses oxygen); oxidising agent: PbO; reducing agent: H₂. (1½)
(b) Oxidised: H₂S (loses hydrogen); reduced: O₂ (gains hydrogen); oxidising agent: O₂; reducing agent: H₂S. (1½)
(c) Oxidised: CO (gains oxygen); reduced: Fe₂O₃ (loses oxygen); oxidising agent: Fe₂O₃; reducing agent: CO. (1)

Answer: See the working.

Example 4: Mass of water · 3 marks · Short answerHarder board level

6 g of hydrogen burns completely in oxygen (4 g H₂ combines with 32 g O₂ to give 36 g H₂O). Find (a) the mass of oxygen needed, (b) the mass of water formed, (c) check conservation of mass.

Try it first, then show the solutionSolution

(a) $\frac{6 \times 32}{4} = 48$ g. (1)
(b) $\frac{6 \times 36}{4} = 54$ g. (1)
(c) $6 + 48 = 54$ g reactants and 54 g product. (1)

Answer: (a) 48 g (b) 54 g (c) 54 g = 54 g

Example 5: A mass loss · 4 marks · Case-basedHOTS / competency

Hydrogen is passed over 8.0 g of heated copper(II) oxide until the solid has turned completely to copper, which weighs 6.4 g. (H = 1, O = 16.) (a) Find the mass of oxygen removed. (b) Find the mass of hydrogen that combined with it and the mass of water formed. (c) Name the oxidised substance. (d) Why would the experiment fail with zinc oxide?

Try it first, then show the solutionSolution

(a) $8.0 - 6.4 = 1.6$ g of oxygen. (1)
(b) H₂O has H : O = 2 : 16, so hydrogen $= \frac{1.6 \times 2}{16} = 0.2$ g; water $= 1.6 + 0.2 = 1.8$ g. (1½)
(c) Hydrogen is oxidised (it gains oxygen). (½)
(d) Zinc is more reactive than copper and holds oxygen more strongly; hydrogen cannot remove it. (1)

Answer: (a) 1.6 g (b) 0.2 g; 1.8 g (c) hydrogen (d) zinc is too reactive

Where students lose marks in Properties and Uses of Hydrogen; Oxidation and Reduction

The slips examiners see most often, and what to write instead.

Mistake: Confusing combustible with supporter
Hydrogen burns but does not support burning.
Wrong working
"Hydrogen supports combustion."
Right working
"Hydrogen burns; it does not support combustion."
Do this: Say both parts.
Mistake: Wrong agent
The reducing agent is oxidised.
Wrong working
"CuO is the reducing agent."
Right working
"H₂ is the reducing agent; CuO is the oxidising agent."
Do this: Ask who gives or takes oxygen.
Mistake: Mass slip
Use the 4 : 32 : 36 ratio.
Wrong working
"6 g H₂ gives 36 g water."
Right working
"6 g H₂ needs 48 g O₂ and gives 54 g water."
Do this: Scale the ratio.

Exam tips

Link every use to a property.
Write both definitions of redox (oxygen and hydrogen).
Name oxidising and reducing agents explicitly.
Quote observations for CuO and hydrogen.

Practice questions on Properties and Uses of Hydrogen; Oxidation and Reduction

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · Very short answerBoard level
How is the presence of hydrogen shown when it is burnt in air?
Hint
Flame and product.
Answer
It burns with a pale blue flame (and a soft pop in a tube), forming water.
Q2 · 2 marks · Short answerHarder board level
Why does hydrogen not reduce the oxides of sodium and magnesium?
Hint
Think of reactivity.
Answer
Sodium and magnesium are very reactive and hold on to oxygen strongly; hydrogen cannot take it away.
Q3 · 3 marks · Short answerHarder board level
Give three uses of hydrogen, each with the property it depends on.
Hint
Match use and property.
Answer
Hydrogenation of oils (it adds to unsaturated oils with nickel). Rocket fuel (burns with great release of heat to form water only). Reducing agent for extracting metals from their oxides.
Q4 · 2 marks · Short answerHarder board level
Why is helium used in balloons now rather than hydrogen?
Hint
Safety.
Answer
Hydrogen is highly flammable and explodes with air; helium is non-flammable and almost as light.
Q5 · 2 marks · Assertion-reasonHOTS / competency
Assertion (A): Hydrogen is a combustible gas but does not support combustion.
Reason (R): A burning splinter goes out in a jar of hydrogen, while the hydrogen burns at the mouth of the jar.
(a) A and R true, R explains A
(b) A and R true, R does not explain A
(c) A true, R false
(d) A false, R true
Hint
What happens to the splinter and the gas?
Answer
Both are true and R is the observation that supports A: hydrogen burns (combustible) but the splinter is extinguished (no support). So (a).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Hydrogen is how many times lighter than air?Show answer
About 14 times.
2.Test: burning splinter?Show answer
Goes out; hydrogen burns with a pop.
3.Reducing agent loses or gains oxygen?Show answer
Gains oxygen (is oxidised).
4.Catalyst for hydrogenation?Show answer
Nickel.
5.Temperature of the oxy-hydrogen flame?Show answer
About 2800 °C.

Properties and Uses of Hydrogen; Oxidation and Reduction: frequently asked questions

What are the chemical properties of hydrogen?

It burns with a pale blue flame to form water, does not support combustion, reduces oxides of less reactive metals, and combines with non-metals such as chlorine and nitrogen.

What is oxidation and reduction?

Oxidation is the addition of oxygen or the removal of hydrogen; reduction is the removal of oxygen or the addition of hydrogen.

Why is hydrogen used as a rocket fuel?

It burns with great heat to produce only water, so it is an efficient and clean fuel.