CCEA A Level Chemistry 1.10 Qualitative Tests Exam Questions

About CCEA A Level Chemistry 1.10 Qualitative Tests

Section 1.10 is a distinctive part of the CCEA Unit AS 1 specification: a set of qualitative tests you must know in detail. It covers tests for six gases, flame tests for six metal ions using a nichrome wire, the test for ammonium ions, tests for sulfate, chloride, bromide, iodide and carbonate ions, and starch as a test for iodine. These tests appear throughout the written papers and in the practical units, often in questions that ask you to identify an unknown compound from observations. Learn each test as a procedure with an exact positive result, because vague answers such as 'goes cloudy' without the reagent will not score.

What you need to know

• Gas tests Hydrogen: squeaky pop with a lighted splint. Oxygen: relights a glowing splint. Chlorine: bleaches damp blue litmus (turns red then white). Carbon dioxide: limewater turns milky. Hydrogen chloride: white smoke with concentrated ammonia, damp blue litmus turns red. Ammonia: damp red litmus turns blue, white smoke with HCl.
• Flame tests Clean a nichrome wire in concentrated HCl, dip in the sample and hold in a blue flame. Li+ crimson, Na+ yellow-orange, K+ lilac, Ca2+ brick red, Ba2+ apple green, Cu2+ blue-green.
• Ammonium ions Warm with sodium hydroxide solution; ammonia is released and turns damp red litmus blue.
• Sulfate Add dilute hydrochloric acid then barium chloride solution; a white precipitate of barium sulfate forms.
• Halides Add dilute nitric acid then silver nitrate. Cl- gives white AgCl, soluble in dilute ammonia; Br- gives cream AgBr, soluble in concentrated ammonia; I- gives yellow AgI, insoluble in concentrated ammonia.
• Carbonate and iodine Carbonate: add dilute acid, effervescence, gas turns limewater milky. Iodine: starch solution turns blue-black.

Common mistakes in 1.10 Qualitative Tests

• Forgetting to acidify before adding silver nitrate or barium chloride. Acid removes carbonate ions that would give a false positive precipitate.
• Using sulfuric acid to acidify before the sulfate test. It adds sulfate ions; use hydrochloric acid.
• Saying chlorine turns litmus white without stating it must be damp. The litmus must be damp for bleaching to occur.
• Writing 'goes cloudy' without naming limewater. State the reagent and the full result: limewater turns milky.
• Mixing up cream and yellow precipitates. Use the ammonia solubility test to confirm bromide or iodide.

Try three 1.10 Qualitative Tests exam-style questions