This topic summary covers Topic Summary: Ion Tests within Tests for Ions for GCSE Chemistry. Revise Tests for Ions in Chemical Analysis for GCSE Chemistry with 20 exam-style questions and 14 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 14 of 14
Practice
20 questions
Recall
14 flashcards
Topic Summary: Ion Tests
NaOH Tests (Cations)
- Cu²⁺ = Blue precipitate
- Fe²⁺ = Green precipitate
- Fe³⁺ = Brown/orange precipitate
- Al³⁺ = White; redissolves in excess
- Ca²⁺ = White; stays cloudy
Anion Tests
- CO₃²⁻: add HCl → fizzing + milky limewater
- SO₄²⁻: BaCl₂ + HCl → white precipitate BaSO₄
- Cl⁻: AgNO₃ + HNO₃ → white AgCl
- Br⁻: AgNO₃ + HNO₃ → cream AgBr
- I⁻: AgNO₃ + HNO₃ → yellow AgI
Why Add Acid?
- BaCl₂ test: HCl removes CO₃²⁻ → prevents false white ppt
- AgNO₃ test: HNO₃ removes CO₃²⁻ → prevents false ppt
- Always acidify BEFORE adding the test reagent
Key Ionic Equations
- Ba²⁺ + SO₄²⁻ → BaSO₄(s)
- Ag⁺ + Cl⁻ → AgCl(s)
- Cu²⁺ + 2OH⁻ → Cu(OH)₂(s)
- CO₃²⁻ + 2H⁺ → CO₂ + H₂O