This guide covers IGCSE Chemistry chemical tests. You will revise tests for cations (flame test; NaOH precipitate), anions (carbonate, chloride, sulfate, nitrate), gases (O2, H2, CO2, Cl2, NH3), and how to describe tests clearly in exams.

Key concepts to revise

• Flame test – Li red; Na yellow; K lilac; Ca brick red; Cu green/blue. Use clean wire; dip in sample; hold in flame.
• Cations + NaOH – Cu2+ blue precipitate; Fe2+ green; Fe3+ brown; Ca2+ white (insoluble in excess); Al3+ white (soluble in excess).
• Anions – Carbonate: acid → CO2 (limewater cloudy). Chloride: add HNO3 then AgNO3 → white precipitate (AgCl). Sulfate: add HNO3 then BaCl2 → white precipitate (BaSO4).
• Gases – O2: relight glowing splint. H2: pop with lighted splint. CO2: limewater cloudy. Cl2: bleaches damp litmus. NH3: turns damp red litmus blue.

Exam tips and command words

• Describe – The test for a given ion or gas (what you add; what you observe; positive result).
• State – The colour of a flame or precipitate for a given ion.
• Identify – An ion or gas from the result of a test (e.g. white precipitate with AgNO3 after HNO3 → chloride).
• Explain – Why HNO3 is added before AgNO3 for chloride (to remove carbonate; carbonate would also give precipitate).

Common mistakes

• Confusing cation tests (flame; NaOH) with anion tests (acid; AgNO3; BaCl2).
• Saying CO2 “turns limewater white” (limewater turns cloudy; white precipitate of CaCO3).
• Not stating that for chloride test you add dilute HNO3 first (to remove carbonate).

Revision checklist

• State the flame colour for Li, Na, K, Ca, Cu.
• Describe the test for chloride (HNO3; AgNO3; white precipitate) and for sulfate (HNO3; BaCl2; white precipitate).
• Describe the test for CO2 (limewater cloudy), O2 (relight splint), H2 (pop).
• Describe the precipitate formed when NaOH is added to Cu2+, Fe2+, Fe3+ (colour).

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise chemical test questions, or explore Tutopiya’s learning portal for more revision resources.