Tests for cations and anions

Test for ammonium ions (NH₄⁺)

• Add NaOH and gently warm

• Test gas with damp red litmus paper

• Result: Pungent-smelling gas turns red litmus blue → Ammonia gas released

Flame test for lithium (Li⁺)

• Dip nichrome wire in HCl, then sample

• Place in Bunsen flame

• Result: Crimson red flame

Flame test for sodium (Na⁺)

• Same method

• Result: Yellow-orange flame

Flame test for potassium (K⁺)

• Same method

• Result: Lilac flame

Flame test for calcium (Ca²⁺)

• Same method

• Result: Brick-red or orange-red flame

Flame test for copper(II) (Cu²⁺)

• Same method

• Result: Blue-green flame

Test for Cu²⁺ with NaOH

• Add NaOH dropwise to solution

• Result: Blue precipitate of Cu(OH)₂

Test for Fe²⁺ with NaOH

• Add NaOH

• Result: Green precipitate (Fe(OH)₂), darkens on standing

Test for Fe³⁺ with NaOH

• Add NaOH

• Result: Brown precipitate (Fe(OH)₃)

Test for carbonate (CO₃²⁻)

• Add dilute acid (e.g. HCl)

• Result: Effervescence → gas turns limewater milky (CO₂)

Test for sulfate (SO₄²⁻)

• Add dilute HCl (removes carbonates), then BaCl₂

• Result: White precipitate of BaSO₄

Test for chloride (Cl⁻)

• Add dilute nitric acid, then AgNO₃

• Result: White precipitate → dissolves in dilute ammonia

Test for bromide (Br⁻)

• Add dilute nitric acid, then AgNO₃

• Result: Cream precipitate → dissolves in concentrated ammonia

Test for iodide (I⁻)

• Add dilute nitric acid, then AgNO₃

• Result: Yellow precipitate → insoluble in ammonia

Order of anion tests

1. Carbonate (effervescence)

2. Sulfate (BaCl₂)

3. Halides (AgNO₃)
   👉 Prevents false positives due to precipitate formation