2.6.6Inorganic Chemistry
Practical: Prepare Copper(II) Sulfate — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions
5 min read 6 parts Lesson 33 of 52
Part 1 of 4Overview
Aim
- Aim To make a pure, dry sample of blue hydrated copper(II) sulfate crystals.
Equation
- Equation CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)
- Black copper(II) oxide neutralises the acid to give a blue solution.
Apparatus
- Apparatus Beaker, measuring cylinder, spatula and glass rod for the reaction;
- Bunsen burner, tripod, gauze and heatproof mat for heating;
- filter funnel, filter paper and conical flask for filtering;
- evaporating basin for crystallising.
Part 2 of 4Method
1
Pour about 50 cm3 of dilute sulfuric acid into a beaker and warm it gently over a Bunsen burner, without boiling.
2
Add copper(II) oxide a little at a time, stirring after each addition, until the black solid stops dissolving and an excess remains.
3
Filter the mixture into an evaporating basin, so that the excess oxide stays in the filter paper and a clear blue solution passes through.
4
Heat the blue solution gently, or use a water bath, to evaporate some of the water.
5
Test whether it is saturated by dipping a cold glass rod in; crystals forming on the rod show that it is ready.
6
Leave the concentrated solution in a warm place to crystallise slowly, then pour off the leftover solution and dry the crystals with filter paper.
Part 3 of 4Why each step matters
Reasoning
Excess copper(II) oxide
- Excess copper(II) oxide Uses up every drop of acid.
- Unreacted acid would become dangerously concentrated and contaminate the crystals during evaporation.
Warming the acid
- Warming the acid The reaction with oxide is slow in the cold, so gentle heating speeds it up.
Filtering
- Filtering Removes the unreacted solid so that the solution contains only copper(II) sulfate and water.
Slow crystallisation
- Slow crystallisation Gives larger, regularly shaped crystals; fast cooling gives small ones.
Part 4 of 4Results and safety
| Aspect | Details |
|---|---|
| Expected product | Bright blue, regularly shaped crystals of hydrated copper(II) sulfate. |
| Hazard: acid | Dilute sulfuric acid irritates skin and eyes; wear eye protection. |
| Hazard: heating | Do not boil the solution, as hot liquid can spit; use a water bath if possible. |
| Hazard: copper compounds | Copper(II) salts are harmful if swallowed and toxic to aquatic life, so wash hands and dispose of waste carefully. |
| Exam tip | Learn the names of the apparatus so that you can label a diagram. |
Key terms
| Term | Meaning |
|---|---|
| Hydrated | Containing water of crystallisation within the crystal structure. |
| Excess | More of a reactant than is needed to react with all of the other. |
| Filtrate | The solution that passes through the filter paper. |
| Evaporating basin | A shallow dish used for heating a solution to drive off water. |
| Water bath | A beaker of hot water used as a gentle, controlled heat source. |
Avoid these mistakes
1
Adding too little copper(II) oxide so some acid is left over. A suspension of black solid must remain at the end.
2
Evaporating to dryness, which gives a powder rather than crystals.
3
Stating that the filter paper holds the copper sulfate. The salt is dissolved in the filtrate; the paper holds the excess oxide.
4
Boiling the acid vigorously before adding the oxide, which is unsafe and unnecessary.
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