Preparing a Soluble Salt

IGCSE Edexcel Chemistry
2.39 Preparing a pure, dry soluble salt
Key Concept: Use an insoluble base in excess, filter, then crystallise the salt solution to obtain a pure, dry sample.

Section A: Method

1. Outline the steps to prepare copper(II) sulfate crystals from copper(II) oxide and sulfuric acid. [4]
2. Why is the base added in excess? [1]
3. Why is the mixture filtered before evaporation? [1]
4. How do you obtain dry crystals at the end? [2]

Total marks: 8

Mark Scheme

1. Warm acid, add excess CuO until no more reacts, filter, evaporate to concentrate, cool to crystallise [4]
2. To ensure all acid is used up so no acid remains [1]
3. To remove excess, unreacted solid [1]
4. Filter crystals and dry between filter paper / in warm place [2]