Test for Oxygen

Section 1 of 8The test

1

Light a wooden splint, let it burn for a moment, then blow out the flame so the end glows red.

2

Place the glowing splint inside the test tube of gas.

3

Watch the splint: if it relights, the gas is oxygen.

4

If the splint stays dim or goes out, the gas is not oxygen.

Section 2 of 8Why it relights

1Splint is glowing

• Splint is glowing It is hot, but without enough oxygen it cannot burn with a flame.

2Pure oxygen added

• Pure oxygen added The concentration of oxygen is higher than in air, which holds only about 21%.

3Faster combustion

• Faster combustion Burning speeds up and the wood reaches a flame again.

4Splint relights

• Splint relights This is a positive test for oxygen.

Section 3 of 8Making oxygen

Hydrogen peroxide

• Hydrogen peroxide Hydrogen peroxide breaks down into water and oxygen: 2H₂O₂ → 2H₂O + O₂.
• The reaction is slow alone but fast with manganese(IV) oxide as a catalyst.

Collecting it

• Collecting it Oxygen is only slightly soluble in water, so it can be collected over water or with a gas syringe.

Other sources

• Other sources Industry obtains oxygen by cooling air until it liquefies and then separating the gases by fractional distillation.
• Plants also release oxygen during photosynthesis.

Section 4 of 8Gas tests compared

Gas	Test	Positive result
Oxygen	Glowing splint in the gas	Splint relights
Hydrogen	Lit splint at the mouth of the tube	Squeaky pop
Carbon dioxide	Bubble through limewater	Limewater turns milky
Chlorine	Damp blue litmus paper	Paper bleached white

Section 5 of 8Where oxygen matters

Role of oxygen

Combustion

• Combustion Fuels need oxygen to burn.

Respiration

• Respiration Living things use oxygen to release energy from food.

Oxidation

• Oxidation Metals such as iron gain oxygen when they rust.

Section 6 of 8Making and testing oxygen in the laboratory

1

Place a small amount of manganese(IV) oxide powder in a conical flask fitted with a delivery tube.

2

Add hydrogen peroxide solution through a funnel and quickly replace the bung.

3

Collect the gas that bubbles off in an upturned test tube filled with water, or in a gas syringe.

4

Seal the tube, then test the gas with a glowing splint and record the observation.

5

Remember that the catalyst is not used up, so it can be filtered off and dried at the end.

Section 7 of 8Key terms

Term	Meaning
Glowing splint	A wooden splint with its flame blown out so the tip is still glowing.
Catalyst	A substance that speeds up a reaction without being used up.
Decomposition	The breaking down of a compound into simpler substances.
Oxidation	A reaction in which a substance gains oxygen.
Positive test	A result that shows the substance being tested for is present.

Section 8 of 8Exam technique

1

Using a lit splint (with a flame) rather than a glowing splint.

2

Saying oxygen itself burns; it supports combustion.

3

Thinking the splint relights in any gas that is not carbon dioxide.

4

Forgetting that manganese(IV) oxide is a catalyst and is left unchanged.