4 - TEST TUBE REACTIONS FOR CATIONS/ ANIONS

• IDENTIFICATION OF GROUP 2 CATIONS?

  1. Add ammonia solution
  2. Mg (2+): white precipitate (Mg(OH)2)
  3. Ca (2+): no observation
  4. Ba (2+): no observation
  5. Add sodium hydroxide solution
  6. Mg (2+): white precipitate (Mg(OH)2)
  7. Ca (2+): white precipitate (Ca(OH)2)
  8. Ba (2+): no observation
  9. Add sulfuric acid
  10. Mg (2+): no observation
  11. Ca (2+): no observation
  12. Ba (2+): white precipitate (BaSO4)
• IDENTIFICATION OF AMMONIUM CATION?

  • add sodium hydroxide solution
  • warm
  • gas evolved with choking smell
  • will turn damp red litmus paper blue
  • NH4+ (aq) + OH- (aq) ⇌ NH3 (g) + H2O (l)
• IDENTIFICATION OF GROUP 7 ANIONS?

  1. Add acidified silver nitrate
  2. F- : no change (AgF is soluble)
  3. Cl- : white precipitate (AgCl)
  4. Br- : cream precipitate (AgBr)
  5. I- : pale yellow precipitate (AgI)
  6. Add dilute ammonia solution
  7. F- : no change
  8. Cl- : white precipitate dissolves
  9. Br- : no change
  10. I- : no change
  11. Add concentrated ammonia solution
  12. F- : no change
  13. Cl- : no change
  14. Br- : white precipitate dissolves
  15. I- : no change
• WHAT IS SILVER NITRATE ACIDIFIED WITH AND WHY?

  • nitric acid
  • removes other present ions
  • e.g. CO3 (2-) or OH-
• OTHER TEST FOR GROUP 7 ANIONS?

  • add sulfuric acid to solid halide compound

  1. F- : steamy acidic fumes of HF
  2. Cl- : steamy acidic fumes of HCl
  3. Br- : orange fumes of Br2 (g)
  4. I- : purple fumes of I2 (g)
• IDENTIFICATION OF HYDROXIDE IONS?

  • add small amount of ammonium chloride
  • gas evolved with choking smell
  • turns damp red litmus paper blue
  • NH4+ (aq) + OH- (aq) ⇌ NH3 (g) + H2O (l)
• IDENTIFICATION OF CARBONATE IONS?

  • add dilute HCl
  • bubble evolved gas through limewater
  • effervescence, limewater turns cloudy due to white precipitate
  • 2H+ (aq) + CO3 (2-) (aq) -> CO2 (g) + H2O (l)
  • CO2 (g) + Ca(OH)2 (aq) -> CaCO3 (s) + H2O (l)
• IDENTIFICATION OF SULFATE IONS?

  • add dilute HCl
  • add BaCl2 solution
  • white precipitate of BaSO4 forms
  • Ba (2+) (aq) + SO4 (2-) (aq) -> BaSO4 (s)