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Qualitative Analysis

Learn how to identify cations and anions through reactions producing insoluble salts. Understand testing methods for ions such as Li+, Na+, Cu2+, Cl-, CO32-, and more using specific chemical reactions. Enhance your knowledge of qualitative analysis in chemistry.

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Qualitative Analysis

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  1. Qualitative Analysis • Reactions that produce an INSOLUBLE SALT

  2. Cations and Anions • When ionic compounds are dissolved into a solutionthey form cationsand anions • Cations(like metalsions) have a positivecharge • Anions(like non-metalgroups) have negativecharges

  3. Remember! • You will need to remember the colour of the precipitate formed for these metals? • REMEMBER: Common hydroxides are INSOLUBLE so they form precipitates Pale blue precipitate of Cu(OH)2 Dirty green precipitate of Fe(OH)2 Rusty brown precipitate of Fe(OH)3

  4. Tests for cations (+ve ions) • Li+, Na+, K+, Ca2+ using flame tests • NH4+ using NaOH(aq) • Cu2+, Fe2+ and Fe3+ using NaOH(aq)

  5. Testing for NH4+ (“ammonium ion”) • Add NaOH (aq) • Warm gently • Test gas given off with dampred litmus paper • Ammonia gas is given off which turns the damp red litmus paper BLUE Does anyone know why the litmus paper changes colour?

  6. Testing for Cl- ions • Add SMALL amounts of silvernitratesolution to salts containing halogenions that have been dissolvedindilutenitricacid.

  7. Testing for sulphate ions SO42-(aq) • Add SMALL amounts of bariumchloridesolutionto salts containing sulphate ions that have been dissolvedindilutehydrochloricacid. • If sulphate ions are present, a whiteprecipitate of barium sulphate is formed.

  8. Testing for NO3- (nitrate ions) • Add NaOH (aq) • Add some SMALL pieces of aluminium foil • Warm gently • Test gas given off with dampred litmus paper • Ammonia gas is given off which turns the damp red litmus paper BLUE

  9. Testing for carbonate ions CO32-(aq) • Add dilutehydrochloricacid • See if it is effervescent (fizzes due to carbondioxide gas being given off)

  10. Testing for anions - Summary • Chloride (Cl-) using dilute nitric acid and silver nitrate solution • Sulphate (SO42-) using dilute hydrochloric acid and barium chloride solution • Carbonate (CO32-) using dilute hydrochloric acid and identifying the carbon dioxide evolved • Nitrate (NO3-) using NaOH and aluminum, then warming gently

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