SASS Chem P3 Tests for Known Anions

Sec 4 Chem Experiment 5.3: Tests for Known Anions 1 St Andrew’s Secondary School Department of Science, Chemistry Name: ________________________( ) Class: _______ Date: __________ Aim: To conduct anion tests to deduce the anion present in each solution Test for aqueous anions Anion Test Observations Chloride (Cl -) Add nitric acid and then silver nitrate NOTE: Lead(II) nitrate is not used because the white ppt formed could either by PbCl2 or PbSO4. Lead(II) nitrate test is therefore inconclusive. White ppt is formed. Implications: White ppt formed is AgCl Ionic equation is: Cl- (aq) + Ag+ (aq)  AgCl (s) aq. Chloride ions (from the unknown solution) will react with aq Silver ions (from silver nitrate) to form an insoluble ppt AgCl. This is a precipitation reaction. Iodide (I - ) Add nitric acid and then silver nitrate Light yellow ppt is formed. Implications: Pale yellow ppt formed is AgI Ionic equation: I- (aq) + Ag+ (aq)  AgI (s) aq. Iodide ions (from the unknown solution) will react with aq Silver ions (from silver nitrate) to form an insoluble ppt AgI. This is a precipitation reaction. Add nitric acid and then lead (II) nitrate solution Bright yellow ppt is formed. Implications: Bright yellow ppt formed is PbI2 Ionic equation: I- (aq) + Pb2+ (aq)  PbI2 (s) aq. Iodide ions (from the unknown solution) will react with aq lead ions (from lead(II) nitrate) to form an insoluble ppt PbI2. This is a precipitation reaction.

Sec 4 Chem Experiment 5.3: Tests for Known Anions 2 St Andrew’s Secondary School Department of Science, Chemistry Nitrate (NO3-) Add Aluminium powder/foil and warm with sodium hydroxide Or Add Devarda’s Alloy (alloy containing Al, Zn and Cu) and warm with sodium hydroxide A colourless, pungent gas is evolved. Gas turns moist red litmus paper blue. Implications: Gas formed is ammonia gas. Sulfate (SO42-) Add nitric acid and barium nitrate Or Add hydrochloric acid and barium chloride White ppt is formed. Implications: White ppt is BaSO4 Ionic equation: Ba2+ (aq) + SO42- (aq)  BaSO4 (s) aq. Iodide ions (from the unknown solution) will react with aq lead ions (from lead(II) nitrate) to form an insoluble ppt PbI2. This is a precipitation reaction. Carbonate (CO32-) Add any acid A colourless, odourless gas is evolved. Gas forms a white ppt with limewater. Implications: Gas formed is carbon dioxide. Metal carbonate + Acid  Salt + H2O + CO2

Sec 4 Chem Experiment 5.3: Tests for Known Anions 3 St Andrew’s Secondary School Department of Science, Chemistry Solutions of Anion Tests Observations nitrate NO3- To 2cm3 of the solution, add dilute aqueous sodium hydroxide. Add 2 small pieces of aluminium foil. Warm the mixture gently and test the gas produced with a piece of damp/moist red litmus paper. carbonate CO32-