Required Practical 7 & Instrumental Methods [Chemistry only]

Required Practical 7: identifying the ions in an unknown compound

• The task: use the chemical tests to identify both ions in an unknown single ionic compound
• A sensible order:
  • Flame test a little of the solid on a clean nichrome wire. A clear colour identifies Li, Na, K, Ca or Cu
  • Dissolve some of the solid in distilled water and add sodium hydroxide dropwise, then in excess: coloured precipitates for Cu, Fe(II), Fe(III); white for Al, Ca, Mg, with only Al redissolving
  • Add dilute acid to a fresh portion: fizzing means a carbonate; confirm with limewater
  • To a fresh solution add nitric acid then silver nitrate: white, cream or yellow means chloride, bromide or iodide
  • To a fresh solution add hydrochloric acid then barium chloride: a white precipitate means sulfate
• Use a fresh sample for each test, and clean the wire between flame tests so colours are not carried over
• Safety: eye protection; silver nitrate stains skin; barium compounds are toxic; keep the Bunsen on a blue flame only while testing