Thursday, 16 May 2013

2.37 describe tests for the cations

i) Li+, Na+, K+, Ca2+ using flame tests
  • Lithum: red
  • Sodium: orange (so strong can mask other colours)
  • Potassium: lilac
  • Calcium: brick red

ii) NH4+, using sodium hydroxide solution and identifying the ammonia evolved
  • NH4 + OH > NH3 + H2O
  • ammonium ions + hydroxide ions > ammonia + water
  • ammonia (pungent smelling gas) turns red litmus paper blue

iii) Cu2+, Fe2+ and Fe3+, using sodium hydroxide solution
  • Copper(ii) sulphate + sodium hydroxide > blue precipitate
  • Iron(ii) sulphate + sodium hydroxide > green precipitate
  • Iron(iii) sulphate + sodium hydroxide > brown precipitate


  1. For the ammonia detecting the red litmus has to be damp btw.

    Thanks for all the help! Your blog is a life saver :)

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