| Ion | Reagent | Positive Result | Key Equation |
|---|---|---|---|
| Cu²⁺ | NaOH(aq) | Blue precipitate | Cu²⁺ + 2OH⁻ → Cu(OH)₂(s) |
| Fe²⁺ | NaOH(aq) | Green precipitate | Fe²⁺ + 2OH⁻ → Fe(OH)₂(s) |
| Fe³⁺ | NaOH(aq) | Brown/orange precipitate | Fe³⁺ + 3OH⁻ → Fe(OH)₃(s) |
| Al³⁺ | NaOH(aq) | White precipitate; redissolves in excess | Al³⁺ + 3OH⁻ → Al(OH)₃(s) |
| Ca²⁺ | NaOH(aq) | White precipitate (stays) | Ca²⁺ + 2OH⁻ → Ca(OH)₂(s) |
| CO₃²⁻ | Dilute HCl | Fizzing; gas turns limewater milky | CO₃²⁻ + 2H⁺ → CO₂ + H₂O |
| SO₄²⁻ | BaCl₂ + HCl | White precipitate of BaSO₄ | Ba²⁺ + SO₄²⁻ → BaSO₄(s) |
| Cl⁻ | AgNO₃ + HNO₃ | White precipitate of AgCl | Ag⁺ + Cl⁻ → AgCl(s) |
| Br⁻ | AgNO₃ + HNO₃ | Cream precipitate of AgBr | Ag⁺ + Br⁻ → AgBr(s) |
| I⁻ | AgNO₃ + HNO₃ | Yellow precipitate of AgI | Ag⁺ + I⁻ → AgI(s) |
This comparison covers All Ion Tests: Full Reference 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 is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 6 of 15 in this topic. Use this comparison to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Tests for Ions
Which reagents are used to test for carbonate ions in a solution?
Describe how sodium hydroxide solution can be used to distinguish between iron(II) ions and iron(III) ions in solution, including the expected observations.
Quick recall flashcards
How do you test for sulfate ions (SO₄²⁻)?
Add barium chloride solution + dilute HCl. White precipitate of BaSO₄ forms. Equation: Ba²⁺ + SO₄²⁻ → BaSO₄(s)
What is a precipitation reaction?
A reaction where two soluble ionic compounds react to form an insoluble precipitate. General form: A⁺(aq) + B⁻(aq) → AB(s)