This exam focus covers Exam Focus 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 13 of 15 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
🎯 Exam Focus
Very High Frequency
What Examiners Ask About Ion Tests
- "Describe tests to identify the ions present in an unknown compound" — state reagent and expected result for each test (4–6 marks)
- "Explain why dilute HCl is added before BaCl₂" — prevents false positive from carbonate ions (2 marks)
- "What colour precipitate forms when NaOH is added to Fe²⁺?" — green (1 mark)
- "How would you distinguish Al³⁺ from Ca²⁺?" — add excess NaOH; only Al(OH)₃ redissolves (2 marks)
- Write ionic equations for precipitation reactions (2 marks)
- "A student observes a yellow precipitate with AgNO₃/HNO₃. Which halide is present?" — iodide (1 mark)
Edexcel 1CH0: Examined in Paper 2 (1CH0/2). Edexcel CP12 also covers precipitation reactions for metal ions and tests for carbonate, sulfate, halide, and ammonium ions — systematic identification questions are common. In Edexcel-style questions, the command word "Suggest" appears frequently — use your chemistry knowledge to apply to an unfamiliar context.
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.