Chemistry 3 Chemistry in action/C3: Topic 1-Qualitative analysis/C3.1 Water testing

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  • Food is tested for purity and safety in chemical analysis.
  • Qualitative analysis checks the type of substances in the sample.
  • Quantitative analysis measures the amount of the substances in the sample.
  • Water sometimes contains ionic compounds which are made of cations and anions.
  • An analyst must test for each ion to identify an unknown ionic compound. Both anion and cation must be identified.
  • Ion tests must only give one positive result to identify the compound.
  • Flame tests can detect some cations.

Calcium:

  • Symbol: Ca2+
  • Flame colour: Brick red

Sodium:

  • Symbol: Na+
  • Flame colour: Yellow

Potassium:

  • Symbol: K+
  • Flame colour: Lilac

Copper:

  • Symbol: Cu2+
  • Flame colour: Green/Blue
  • Sodium hydroxide can be added to the solution to find the unknown cations
  • Many metal hydroxides are insoluble so a precipitation reaction can occur.
  • The precipitate formed can identify the ion.

Aluminium:

  • Symbol: Al3+(aq)
  • Effect: White precipitate

Calcium:

  • Symbol: Ca2+(aq)
  • Effect…

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