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CAIE IGCSE Chemistry Gas Tests and Observations

Practise identifying common laboratory gases from splint tests, litmus or limewater changes and decolourisation of acidified manganate(VII).

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • identify hydrogen by a squeaky pop with a lighted splint and oxygen by relighting a glowing splint
  • identify ammonia with damp red litmus, carbon dioxide with limewater and chlorine by bleaching damp litmus
  • identify sulfur dioxide by decolourising acidified potassium manganate(VII) from purple to colourless

12.5.3—Gas tests: NH3 with damp red litmus question 1

[Maximum number: 2]

Hydrogen can be manufactured from methane by steam reforming.

CH4( g)+H2O( g)⇌CO( g)+3H2( g)\mathrm{CH}_{4}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \rightleftharpoons \mathrm{CO}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g})

The reaction is carried out using a nickel catalyst at temperatures between 700∘C700^{\circ} \mathrm{C} and 1100∘C1100^{\circ} \mathrm{C} and using a pressure of one atmosphere.

The forward reaction is endothermic.

Hydrogen can also be manufactured by electrolysis. The electrolyte is concentrated aqueous sodium chloride. The electrodes are inert.

The products of electrolysis are hydrogen, chlorine and sodium hydroxide.

Describe a test for chlorine.
test
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