Chemical Tests and Flame Tests

Metal Ion Flame Colours

• Li⁺ : Red

• Na⁺ : Yellow/orange

• K⁺ : Lilac

• Rb⁺ : Red/purple

• Cs⁺ : Blue/violet

• Be²⁺ : No colour

• Mg²⁺ : No colour

• Ca²⁺ : Brick red

• Sr²⁺ : Crimson red

• Ba²⁺ : Apple green

• Cu²⁺ : Blue/green

• Pb²⁺ : Greyish white

Tests for Halides

• Method:

1. Add HNO₃.

2. Then add AgNO₃.

• Results:

  • Chloride: White precipitate - dissolves in DILUTE NH₃.

  • Bromide: Cream precipitate - dissolves in CONCENTRATED NH₃.

  • Iodide: Yellow precipitate - does not dissolve in any NH₃.

Test for Ammonium Ions (NH₄⁺)

• Method:

1. Add NaOH solution and warm.
   NH₄^+ + OH⁻ \rightarrow NH₃ + H₂O
   Ammonia gas should turn red litmus paper blue.
   Alternatively, use hydrogen chloride gas:
   NH₃ + HCl \rightarrow NH₄Cl
   Forms white fumes of ammonium chloride.

Test for Carbonates (CO₃²⁻)

• Method:

1. Add HCl (or any other acid).
   Produces CO₂ which turns limewater cloudy.
   The reverse can also be used for testing acids: add carbonate.

Test for Sulphates (SO₄²⁻)

Method:

1. Add barium chloride and dilute HCl.

2. A white precipitate (BaSO₄) forms.

Tests for Alcohols

Method:

1. Add PCl₅: white misty fumes form.
   OR add acidified dichromate and heat under distillation.
   Results:

• Orange solution turns green (primary and secondary alcohols only).

Test for Alkenes

Test:
Add bromine water.

Result:

• Orange → colourless.

Test for Haloalkanes

Method:

1. Dissolve in ethanol.

2. Add water, then complete the test for halides.

Methyl-Ketone Test (Iodoform Test)

Method:

• Add NaOH and I₂ and warm.

Result:

• Yellow precipitate forms.

Test for Aldehydes

Method:

1. Use Tollen's reagent:
   Silver nitrate, 1 drop of sodium hydroxide, ammonia solution dropwise (until precipitate dissolves).

2. Add unknown organic substance and wait 5 minutes.

Result:

• A silver mirror should form.

Test for Carboxylic Acids

Method:

1. Mix equal volumes of unknown substance and ethanol.

2. Add a few drops of sulfuric acid.

3. Heat mixture in hot water, then pour into a boiling tube containing aqueous sodium carbonate.

Result:

• Should smell like an ester (sweet, fruity smell).