Exam Focus

🎯 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.