Precipitation Reactions

Cards made for GCSE OCR gateway science chemistry on Precipitation Reactions

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  • Created by: Lucy :)
  • Created on: 31-05-13 11:49

Precipitation Reactions

  • 2 solutions react together to make an insoluble substance - precipitate
  • the precipitate makes the solution turn cloudy
  • most precipitate reactions involve ions

barium chloride + sodium sulfate -> barium sulfate + sodium chloride

     BaCl2 (aq)   +  Na2SO4 (aq)   ->    BaSO4 (s)   + 2NaCl (aq)

  • sodium and chloride ions were dissolved in solution before the reaction = they're still dissolved afterwards
  • ^ called spectator ions - as they don't change during the reaction
  • An ionic equation ignores the spectator ions:

Ba^2+ (aq) + SO4^2- (aq) --> BaSO4 (s)

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Testing for sulfates and halides

Test for Sulfate ions, SO4^-

  • add dilute HCl
  • then barium chloride, BaCl2
  • white precipitate of barium sulfate means the origninal compound was a sulfate

Test for Chloride (Cl^-), Bromide (Br^-) or Iodide (I^-) ions

  • add dilute nitric acid
  • followed by lead nitrate
  • Chorlide = white percipitate of lead chloride
  • Bromide = cream precipitate of lead bromide
  • Iodide = yellow precipitate of lead iodide
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