Home · IGCSE Chemistry 0620 · Experimental techniques and chemical analysis · Tests for gases · Practice
IGCSE · Practice questions · Tests for gases

Name the gas.

Six original Cambridge-style questions on testing for gases.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Splints, litmus, limewater, manganate.

01
Recall
[2 marks]

Describe the tests for hydrogen and for oxygen, giving the result of each.

  • Hydrogen: hold a lighted splint at the mouth of the tube; there is a squeaky pop. ✓
  • Oxygen: put a glowing splint into the gas; it relights. ✓
02
Recall
[2 marks]

Describe the test for chlorine and give the result.

  • Hold damp litmus paper in the gas. ✓
  • The litmus is bleached (turns white). ✓
03
Analysis
[2 marks]

A white solid is warmed with aqueous sodium hydroxide. A gas is produced that turns damp red litmus paper blue. Name the gas and the ion present in the solid.

  • The gas is ammonia. ✓
  • The solid contains ammonium ions, NH4+. ✓
04
Explain
[2 marks]

Explain why limewater turns milky when carbon dioxide is bubbled through it. Include an equation.

  • Carbon dioxide reacts with calcium hydroxide (limewater) to form insoluble calcium carbonate. ✓
  • Ca(OH)2 + CO2 → CaCO3 + H2O; the white precipitate makes it milky. ✓
05
Analysis
[3 marks]

Name the gas produced in each reaction and state how you would test for it: (a) magnesium with dilute hydrochloric acid, (b) calcium carbonate with dilute nitric acid, (c) sodium sulfite with dilute hydrochloric acid.

  • (a) hydrogen: lighted splint gives a squeaky pop. ✓
  • (b) carbon dioxide: limewater turns milky. ✓
  • (c) sulfur dioxide: acidified aqueous potassium manganate(VII) turns from purple to colourless. ✓
06
Analysis
[2 marks]

A student tests a gas with dry red litmus paper and sees no change, then concludes the gas is not ammonia. Explain why this conclusion may be wrong.

  • The litmus paper was dry; ammonia must dissolve in water to form an alkaline solution. ✓
  • The test should be repeated with damp red litmus paper. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.