2.7.8Inorganic Chemistry
Practical: Prepare Copper(II) Sulfate — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions
5 min read 6 parts Lesson 22 of 23 Unit quiz
Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
Section 1 of 6The Chemistry
An insoluble base plus an acid forms a soluble salt and water.
Reaction
- Reaction Copper(II) oxide is an insoluble base: CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l).
Excess base
- Excess base The solid is added in excess so that all of the acid is used up and the final product is not acidic.
Product
- Product The salt crystallises as bright blue hydrated crystals, CuSO₄·5H₂O.
Warming
- Warming The acid is warmed gently to speed up the reaction, which is slow in the cold.
Section 2 of 6Method
Each step removes a possible impurity.
1
Measure 50 cm³ of dilute sulfuric acid into a beaker and warm gently with a Bunsen burner.
2
Add copper(II) oxide a little at a time, stirring, until no more dissolves and some black solid remains.
3
Filter the mixture to remove the excess copper(II) oxide, collecting the blue filtrate in an evaporating basin.
4
Heat the filtrate gently to evaporate some water until a drop on a cold glass rod forms crystals.
5
Leave the saturated solution in a warm place to crystallise.
6
Decant the remaining liquid and dry the crystals.
Section 3 of 6Apparatus and Safety
Apparatus and Safety
Apparatus
- Apparatus Beaker, spatula, glass rod, funnel and filter paper, evaporating basin, Bunsen burner, tripod, gauze and heatproof mat.
Safety
- Safety Wear eye protection, as sulfuric acid and copper salts are harmful, and do not heat the acid strongly.
Why not evaporate to dryness
- Why not evaporate to dryness Strong heating would remove the water of crystallisation and could decompose the salt.
Crystals
- Crystals Allowing the solution to cool slowly gives larger and more regular crystals.
| Observation | Explanation |
|---|---|
| Black solid disappears | CuO reacts with acid to form soluble CuSO₄ |
| Blue solution forms | Copper(II) ions are present in solution |
| Black solid left | The base is in excess, so the acid is used up |
Section 4 of 6Evaluating the Preparation
Evaluating the Preparation
Percentage yield
- Percentage yield Percentage yield is actual mass divided by theoretical mass, multiplied by 100.
Losses
- Losses Some product is lost in transfers, on filter paper, in remaining solution and by incomplete crystallisation.
Purity
- Purity The crystals are pure if the excess solid was fully removed and washed away.
Section 5 of 6Worked Example
Question
- 50 cm³ of 1.0 mol/dm³ sulfuric acid reacts with excess copper(II) oxide and 9.0 g of CuSO₄·5H₂O is obtained.
- Calculate the percentage yield.
- (Ar: Cu = 63.5, S = 32, O = 16, H = 1)
- Moles of H₂SO₄ = 1.0 × 50 ÷ 1000 = 0.050 mol, so moles of CuSO₄·5H₂O = 0.050 mol.
- Mr of CuSO₄·5H₂O = 63.5 + 32 + 64 + (5 × 18) = 249.5.
- Theoretical mass = 0.050 × 249.5 = 12.5 g.
- Percentage yield = 9.0 ÷ 12.5 × 100 = 72%.
Answer Percentage yield = 72% (to 2 s.f.)
Section 6 of 6Exam Checklist & Tips
2.7.8 – Key Points for the Exam
- Insoluble base A base that does not dissolve in water, such as copper(II) oxide.
- Excess More than is needed to react completely.
- Hydrated Containing water of crystallisation within the crystal structure.
- Filtrate The solution that passes through the filter paper.
Common Mistakes
- Adding too little copper(II) oxide, leaving acid in the final solution.
- Evaporating all the water instead of leaving the solution to crystallise.
- Forgetting the water of crystallisation when calculating the relative formula mass.
- Describing the excess solid as a precipitate rather than unreacted base.
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