6.3.1 — Reversible Reactions & Salts
Cambridge IGCSE Chemistry 0620 · Papers 2 & 4
Quick Reference
Quick Reference
🧠 The Golden Memory Trick
🔵→⬜
CuSO₄
Anhydrous = White
Hydrated = Blue
🩷→🔵
CoCl₂
Anhydrous = Blue
Hydrated = Pink
Q1.State the colour of anhydrous copper(II) sulfate.
Q2.State the colour of hydrated copper(II) sulfate, CuSO₄·5H₂O.
Q3.State the colour change observed when water is added to anhydrous copper(II) sulfate.
Q4.What type of reaction occurs when hydrated copper(II) sulfate crystals are heated?
Q5.Write the equation for the reversible dehydration of hydrated copper(II) sulfate.
Q6.State the colour of anhydrous cobalt(II) chloride.
Q7.State the colour of hydrated cobalt(II) chloride, CoCl₂·6H₂O.
Q8.State the colour change when anhydrous cobalt(II) chloride is exposed to moisture in the air.
Q9.Cobalt chloride paper is used as an indicator. Describe the test and result that shows water is present.
Q10.Write the equation for the reversible hydration of anhydrous cobalt(II) chloride.
Q11.What does the symbol ⇌ represent in a chemical equation?
Q12.What substance are the reactions of copper(II) sulfate and cobalt(II) chloride commonly used to test for?
Q13.A student adds a few drops of liquid from a bottle to blue cobalt chloride paper. The paper turns pink. What conclusion can the student draw?
Q14.Explain why the conversion of anhydrous copper(II) sulfate to hydrated copper(II) sulfate is described as a reversible reaction.
Q15.A technician needs to check whether a gas produced in an experiment contains water vapour. Describe the test, including the reagent used, the method, and the expected result if water is present.
📊 Exam Summary
5
CuSO₄ Questions
5
CoCl₂ Questions
5
Symbols & Uses
Total: 24 marks · Cambridge IGCSE 0620 · Topic 6.3.1
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