Core Practical 7 – Identify Unknown Organic Liquids and Inorganic Solids

Safety Notes

• Wear eye protection at all times.
• Treat all unknown organic liquids as harmful and flammable.
• Inorganic solids may be harmful.
• Reagents used include:
  • Potassium dichromate – corrosive, carcinogenic, oxidising
  • Potassium manganate(VII) – oxidising
  • Silver nitrate – corrosive
  • Chlorine water – toxic
  • Ethanol – flammable
  • Dilute ammonia – irritant gas
  • Barium chloride – harmful

Part 1 – Organic Identification (A, B, C)

Test 1 – Unsaturation (Alkenes)

• Add bromine water to 10 drops of the liquid.
• Positive result: Decolorisation → presence of C=C.

Test 2 – Oxidation (Alcohols)

• Add acidified potassium dichromate and warm.
• Positive result: Orange → green = primary or secondary alcohol.

Test 3 – Aldehyde Test

• Add Fehling’s solution and heat.
• Positive result: Blue → red/orange ppt = aldehyde.

Test 4 – Halogenoalkane Test

• Add ethanol and dilute NaOH, warm, then acidify and add silver nitrate.
• Positive result: Precipitate = halide ion (white = Cl⁻, cream = Br⁻, yellow = I⁻).

Part 2 – Inorganic Identification (X, Y, Z)

Step 1 – Flame Test

• Use a platinum or nichrome wire loop.
• Dip into concentrated hydrochloric acid and place in non-luminous Bunsen flame until no colour observed.
• Dip into sample and place back in flame.
• Observe flame colour:
  • Red-orange = calcium
  • Yellow = sodium
  • Lilac = potassium

Step 2 – Dissolve in water and divide into three portions

(a) Halide test

• Add dilute nitric acid + silver nitrate → ppt forms.
• Add ammonia to check solubility:
  • Cl⁻ = white ppt (soluble in dilute NH₃)
  • Br⁻ = cream ppt (insoluble in dilute NH₃)
  • I⁻ = yellow ppt (insoluble)

(b) Sulfate test

• Add dilute nitric acid + barium chloride.
• Positive result: White ppt = SO₄²⁻.

(c) Halide displacement with chlorine water

• Add chlorine water.
• Positive result: Colour change indicates displacement (e.g. Br⁻ → orange solution, I⁻ → dark brown/purple in solvent).

Sample Results

Organic Liquids

Inorganic Solids

Key Reactions

• Carbonate test: CO₃²⁻ + 2H⁺ → CO₂ + H₂O
• Halide test: Ag⁺ + Br⁻ → AgBr (ppt)
• Sulfate test: Ba²⁺ + SO₄²⁻ → BaSO₄ (white ppt)
• Halide displacement: 2Br⁻ + Cl₂ → Br₂ + 2Cl⁻