Chemical Tests

1. Tests for Gases

• Hydrogen:

  • Test: Insert a lit splint into the gas.

  • Result: A squeaky pop sound indicates hydrogen.

• Oxygen:

  • Test: Insert a glowing splint into the gas.

  • Result: The splint relights in the presence of oxygen.

• Carbon Dioxide:

  • Test: Bubble the gas through limewater (calcium hydroxide solution).

  • Result: Limewater turns cloudy/milky.

• Chlorine:

  • Test: Hold damp litmus paper in the gas.

  • Result: The litmus paper is bleached white.

2. Tests for Positive Ions (Cations)

Flame Tests

• Lithium (Li⁺): Crimson-red flame

• Sodium (Na⁺): Yellow-orange flame

• Potassium (K⁺): Lilac flame

• Calcium (Ca²⁺): Brick-red flame

• Copper (Cu²⁺): Green flame

Precipitation Reactions with Sodium Hydroxide (NaOH)

• Calcium (Ca²⁺): White precipitate (does not dissolve in excess NaOH)

• Copper(II) (Cu²⁺): Blue precipitate

• Iron(II) (Fe²⁺): Green precipitate

• Iron(III) (Fe³⁺): Brown precipitate

• Aluminium (Al³⁺): White precipitate (dissolves in excess NaOH)

• Magnesium (Mg²⁺): White precipitate (does not dissolve in excess NaOH)

3. Tests for Negative Ions (Anions)

Carbonates (CO₃²⁻):

• Test: Add dilute acid (e.g., HCl).

• Result: Effervescence (bubbles of carbon dioxide). Confirm CO₂ with limewater.

Sulfates (SO₄²⁻):

• Test: Add dilute HCl, then barium chloride (BaCl₂).

• Result: White precipitate of barium sulfate.

Halides (Cl⁻, Br⁻, I⁻):

• Test: Add dilute nitric acid (HNO₃), then silver nitrate (AgNO₃).

  • Chloride (Cl⁻): White precipitate

  • Bromide (Br⁻): Cream precipitate

  • Iodide (I⁻): Yellow precipitate

4. Tests for Water

• Anhydrous Copper(II) Sulfate:

  • Test: Add to suspected water.

  • Result: White powder turns blue.

• Cobalt(II) Chloride Paper:

  • Test: Hold in the sample.

  • Result: Blue paper turns pink.