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Chemical Tests for Ions and Gases: Question 9

Syllabus 12.5

Multiple choice Core 1 mark

A school laboratory technician reacts a small piece of magnesium ribbon with dilute sulfuric acid in a boiling tube and collects the gas produced. To check the identity of the gas before disposing of the tube's contents, she holds a lit wooden splint to the mouth of the tube.

Which observation would confirm that the gas collected is hydrogen?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Recall the specified test for each gas

Each gas in the options below has one specific confirmatory test:

GasTest and result
hydrogen, H2\text{H}_2burns with a squeaky pop with a lit splint
oxygen, O2\text{O}_2relights a glowing splint
carbon dioxide, CO2\text{CO}_2turns limewater milky
chlorine, Cl2\text{Cl}_2bleaches damp litmus paper

Step 2: Match the test to hydrogen

A reaction between a reactive metal, such as magnesium, and a dilute acid produces hydrogen gas. Holding a lit splint to the mouth of the tube is the standard test: hydrogen ignites and burns rapidly, producing a characteristic squeaky pop.

Why the other options are wrong

  • A: relighting a glowing splint is the specified test for oxygen, not hydrogen. A lit splint is used for hydrogen, and a glowing (not flaming) splint is used for oxygen.
  • C: turning limewater milky is the specified test for carbon dioxide, a gas not produced by this reaction.
  • D: bleaching damp litmus paper is the specified test for chlorine, which is unrelated to a metal-acid reaction.

Final answer

The gas collected is hydrogen\boxed{\text{hydrogen}}, confirmed because it burns with a squeaky pop, option B.