AQA GCSE Chemistry Unit 3 - Identifying Substances

Outlines the different tests you need to know.

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Flame Tests

Used to identify metal ions.

  • Barium - green
  • Calcium - brick red
  • Lithium - red
  • Potassium - lilac
  • Sodium - yellow
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Test for carbonates

  • add hydrochloric acid
  • carbon dioxide gas produced
  • carbon dioxide turns limewater cloudy/milky
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Thermal decomposition reactions

  • Strongly heating copper carbonate in a combustion tube causes it to go black as copper oxide is formed.
  • Strongly heating zinc carbonate in a combustion tube causes it to go yellow as zinc oxide is formed.
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Precipitation of metal ions

Adding sodium hydroxide solution to metal ions forms coloured precipitates (insolube solids)

  • Add sodium hydroxide solution:
  • Aluminium - white
  • Calcium - white
  • Magnesium - white
  • Copper - blue
  • Iron II - green
  • Iron III - brown
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Test for sulfate ions

  • add dilute hydrochloric acid
  • add barium chloride solution
  • white precipitate of barium sulfate is formed
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Test for ammonium ions

  • add sodium hydroxide
  • ammonia gas given off
  • damp red litmus paper turns blue
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Test for nitrate ions

  • add aluminium powder (reduces the ions)
  • add sodium hydroxide solution
  • ammonia is formed
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Test for halide ions

  • add dilute nitric acid
  • add silver nitrate solution
  • precipitates formed:
  • silver chloride - white
  • sliver bromide - cream
  • silver nitride - yellow
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Tests for organic compounds

The surfaces of organic compounds will char if they are burned in air. Black marks can be seen on the surface of organic compounds which are burned as carbon is made.

Bromine water can be used to identify whether organic compounds are saturated or unsaturated:

  • Unsaturated - bromine water goes form brown to colourless
  • Saturated - bromine water stays brown
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haha my one about organic compunds is exactly the same word for word lol x

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