Qualitative Analysis and Cation Tests

Page 1: Qualitative Analysis

Flame Tests

• Li⁺: Red (scarlet)

• Na⁺: Yellow/orange

• K⁺: Lilac

• Mg²⁺: No colour

• Ca²⁺: Brick red

• Sr²⁺: Red (crimson)

• Ba²⁺: Apple-green

Anion Tests

• Sulfate (SO4 ^2-):

  • Ba²⁺: White ppt

• Carbonate (CO₃ ^2-):

  • Any acid: Fizzes (produces CO₂, tested with limewater)

• Hydroxide (OH^-):

  • Mg²⁺: White ppt

• Chloride (Cl^-):

  • AgNO₃: White ppt

• Bromide (Br^-):

  • AgNO₃: Cream ppt

• Iodide (I^-):

  • AgNO₃: Yellow ppt

Note: Carbonate ions can also be identified with group 2 ions in the appropriate context.

Page 2: Cation Tests

Group 2 Tests

• Mg²⁺:

  • OH^-: White ppt

  • SO₄ ^2-: No ppt

  • CO₃ ^2-: White ppt

• Ca²⁺:

  • OH^-: Thin white ppt

  • SO₄ ^2-: Thinner white ppt

  • CO₃ ^2-: White ppt

• Sr2+:

  • OH^-: Thinner white ppt

  • SO4 ^2-: Thin white ppt

  • CO₃ ^2-: White ppt

• Ba2+:

  • OH^-: No ppt

  • SO₄ ^2-: White ppt

  • CO₃ ^2-: White ppt

Notes:

• Be is ignored due to anomalous behaviour.

• All Group 1 compounds are soluble.

NaOH Tests: Appearance of Solution

• Pb²⁺: Colourless, forms white ppt that redissolves in excess reagent (indicates amphoteric nature)

• Al³⁺: Colourless, white ppt that redissolves in excess

• Zn²⁺: Colourless, white ppt that redissolves in excess

• Cr³⁺: Green, forms grey-green ppt that redissolves in excess

• Cu²⁺: Blue, forms blue ppt that does not redissolve in excess (not amphoteric)

• Fe ²⁺: Pale green, grey-green ppt that does not redissolve (turns brown at top)

  Fe ³⁺: Pale brown/orange, orange-brown ppt that does not redissolve

Other reactions to note:

• Pb²⁺ with Cl^-: White ppt

• Pb²⁺ with I^-: Bright yellow ppt

• Cu²⁺ with I^-: White ppt (CuI) with brown solution (iodine)