Specification Point 2.44:
Describe the tests for these gases: Hydrogen, Oxygen, Carbon Dioxide, Ammonia and Chlorine

Test for Hydrogen

Test for hydrogen

The test for Hydrogen


  • Collect gas into a boiling tube
  • Put lit splint inside


  • Burns with a ‘Squeaky Pop’ if hydrogen is present


2H2 (g)    +    O2 (g)     →     2H2O (l)

Test for Oxygen

test for oxygen

The test for Oxygen


  • Collect gas into a boiling tube
  • Insert glowing splint


  • Splint relights if oxygen is present

Test for Carbon Dioxide

Test for carbon dioxide

The test for Carbon Dioxide


  • Bubble gas through limewater
  • Observe colour change


  • Limewater turns milky and cloudy if carbon dioxide is present


Ca(OH)2 (aq)    +    CO2 (g)     →     CaCO3 (s)     +    H2O (l)

*The white solid, CaCO3, turns the limewater milky

Test for Ammonia

Ammonia test, Edexcel IGCSE Chemistry

The test for Ammonia


  • Lower damp red litmus paper or damp universal indicator (pH) paper into test solution


  • Damp red litmus paper turns blue if Ammonia is present
  • Damp universal indicator (pH) paper turns purple if Ammonia is present


NH3 (g)    +    H2O (l)     →     NH4+ (aq)     +    OH (aq)

*The Hydroxide Ions, OH, turns the Litmus Blue

Test for Chlorine

The test for Chlorine


  • Lower damp litmus paper or moist starch-iodide paper into test solution


  • Damp litmus paper is bleached white if chlorine is present
  • Moist starch-iodide paper turns blue if chlorine is present

Equation for moist starch-iodide Paper:

Cl2 (g)    +    2l (aq)     →     2Cl (aq)     +    I2 (aq)

*The iodine formed turns the starch blue

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Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.