Test for Ions

• Ions: Charged atoms; cations are positively charged, anions are negatively charged.

Testing Aqueous Cations

• Common Cations: Calcium (Ca²⁺), Aluminium (Al³⁺), Zinc (Zn²⁺), Copper (Cu²⁺), Iron(II) (Fe²⁺), Iron(III) (Fe³⁺).

Using Aqueous Sodium Hydroxide

1. Procedure: Add a few drops of NaOH to the cation solution.
2. Observations:
   • Copper sulfate (Cu²⁺): Blue precipitate (insoluble).
   • Iron(II) chloride (Fe²⁺): Pale green precipitate (insoluble).
   • Aluminium sulfate (Al³⁺): White precipitate (dissolves in excess).
   • Magnesium sulfate (Mg²⁺): White precipitate (insoluble).
   • Calcium sulfate (Ca²⁺): White precipitate (insoluble).
   • Zinc sulfate (Zn²⁺): White precipitate (dissolves in excess).

Using Aqueous Ammonia

1. Procedure: Add a few drops of ammonia to the cation solution.
2. Observations:
   • Calcium (Ca²⁺): White precipitate (insoluble).
   • Aluminium (Al³⁺): White precipitate (insoluble).
   • Zinc (Zn²⁺): White precipitate (dissolves in excess).
   • Copper (Cu²⁺): Blue precipitate (dissolves in excess).
   • Iron(II) (Fe²⁺): Green precipitate (insoluble).
   • Iron(III) (Fe³⁺): Red-brown precipitate (insoluble).
   • Lead (Pb²⁺): White precipitate (insoluble).

Testing for Anions

• Common Anions: Sulphates, halides, nitrates.

Testing for Sulphate Ions (SO₄²⁻)

• Procedure: Add dilute hydrochloric acid and barium chloride.
• Observation: White precipitate indicates the presence of sulphate ions.

Testing for Halide Ions

• Procedure: Add dilute nitric acid and dilute silver nitrate.
• Observations:
  • Fluoride ions (F⁻): No precipitate.
  • Chloride ions (Cl⁻): White precipitate.
  • Bromide ions (Br⁻): Pale yellow precipitate.
  • Iodide ions (I⁻): Yellow precipitate.

Testing for Nitrates (NO₃⁻)

• Detection Method:
  1. Add aqueous sodium hydroxide to a small amount of the nitrate solution.
  2. Introduce aluminum foil into the mixture.
  3. Warm gently.
• Observation: If nitrate ions are present, ammonia gas will be released. This gas will turn damp red litmus paper blue.

Testing for Gases

Commonly Tested Gases: Ammonia, Carbon Dioxide, Hydrogen, Chlorine, Oxygen, Sulphur Dioxide

1. Testing for Ammonia (NH₃):
   • Method: Introduce damp red litmus paper into a jar containing ammonia.
   • Observation: The damp red litmus paper turns blue.
2. Testing for Carbon Dioxide (CO₂):
   • Method: Bubble the gas through lime water (calcium hydroxide solution).
   • Observation: Lime water turns milky if carbon dioxide is present.
3. Testing for Hydrogen (H₂):
   • Method: Introduce a burning splint at the mouth of a gas jar containing hydrogen.
   • Observation: A ‘pop’ sound indicates the presence of hydrogen.
4. Testing for Chlorine (Cl₂):
   • Method: Hold damp blue litmus paper at the mouth of a test tube containing chlorine gas.
   • Observation: The damp blue litmus paper gets bleached.
5. Testing for Oxygen (O₂):
   • Method: Introduce a glowing splint into a gas jar containing oxygen gas.
   • Observation: The glowing splint relights (bursts into flames).
6. Testing for Sulphur Dioxide (SO₂):
   • Method: Bubble the gas through acidified potassium dichromate (VII) solution.
   • Observation: The solution changes from purple to colorless if sulphur dioxide is present.

Testing for the Presence of Water

Using Anhydrous Copper (II) Sulphate and Anhydrous Cobalt (II) Chloride

1. Anhydrous Copper (II) Sulphate (CuSO₄):
   • Observation: Anhydrous copper (II) sulphate is white and turns blue upon the addition of water, indicating the presence of water.
2. Anhydrous Cobalt (II) Chloride (CoCl₂):
   • Observation: Anhydrous cobalt (II) chloride is blue and turns pink when water is added, confirming the presence of water.