3.1.4

Test for ions

(a)(i)→test for carbonates:

  • 1cm³ of dilute HCl and NaCO3 added to test tube via pipette

  • attach test tube to a delivery tube

  • transfer gas formed into different test tube w small amount of limewater

  • if carbonate present then gas produced is CO2 and white precipitate of calcium carbonate [image]

  • CO32- (aq) + 2H+ (aq) → CO2 (g) + H2O (l)

  • CO2 (g) + Ca(OH)2 (aq) → CaCO3 (s) + H2O (l)

→test for sulfates:

  • acidify sample with dilute HCl

  • add few drops of aq BaCl

  • if sulphate present then white precipitate of BaSO4 formed

(ii)→test for ammonium ions NH4+:

  • reacting w warm aq NaOH forming ammonia gas

  • NH4+ (aq) + OH- (aq) → NH3 (g) + H2O (l)

  • ammonia gas identified by pungent smell or by turning red litmus paper blue