This question is about copper and copper compounds.
(a) Describe how you could prepare a pure sample of crystals of hydrated copper(II) sulfate using dilute sulfuric acid and an excess of copper(II) oxide. [3]
(b) Anhydrous copper(II) sulfate is used to test for water.
$\begin{aligned} & \mathrm{CuSO}_4+5 \mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O} \\ & \text{anhydrous} \quad \text{hydrated} \\ & \text{copper(II) sulfate} \quad \text{copper(II) sulfate} \end{aligned}$
(i) What is meant by the symbol $\rightleftharpoons$? [1]
(ii) How can hydrated copper(II) sulfate be changed into anhydrous copper(II) sulfate? [1]
(c) Complete the table to calculate the relative formula mass of anhydrous copper(II) sulfate, $\mathrm{CuSO}_4$.
relative formula mass = …………………………. [2]
(d) Complete the table to show the number of electrons, protons and neutrons in the sulfur atom and copper ion shown.
(e) Alloys of copper are used to make coins.
(i) What is meant by the term alloy? [1]
(ii) Suggest why an alloy of copper is used to make coins instead of using pure copper. [1]
▶️ Answer/Explanation
(a) Preparation method:
1. React excess CuO with dilute H₂SO₄ until no more dissolves (neutralization)
2. Filter to remove excess CuO, obtaining blue CuSO₄ solution
3. Heat solution to saturation point, then cool to crystallize hydrated CuSO₄·5H₂O
(b)(i) The symbol $\rightleftharpoons$ indicates a reversible reaction where the forward (hydration) and reverse (dehydration) processes can occur.
(b)(ii) Heat gently to about 200°C – This removes water of crystallization, converting the blue hydrated form to white anhydrous powder.
(c) Relative formula mass calculation:
Cu (63.5) + S (32) + 4×O (4×16) = 63.5 + 32 + 64 = 159.5 ≈ 160
(d) Particle counts:
Sulfur atom (¹⁶₃₂S): 16p⁺, 16e⁻, 16n⁰
Copper ion (⁶⁵₂₉Cu²⁺): 29p⁺, 27e⁻ (lost 2 electrons), 36n⁰ (65-29)
(e)(i) An alloy is a homogeneous mixture of a metal with other elements (metals or non-metals) to enhance properties.
(e)(ii) Copper alloys are used because they’re harder and more durable than pure copper, resisting wear better in circulation.
This question is about zinc and compounds of zinc.
(a) Zinc is a metal.
Give three physical properties of metals.[3]
(b) Zinc reacts with phosphorus to form zinc phosphide, Zn3P2.
Complete the equation for this reaction.[2]
Zn + P → Zn3P2
(c) Molten zinc chloride is electrolyzed.
The incomplete apparatus is shown.
(i) Complete the diagram by:[2]
completing the circuit to show the wires and power pack
labelling the anode.
(ii) Name the products formed at each electrode.[2]
positive electrode
negative electrode
(d) Zinc chloride reacts with water as shown. The solution formed is acidic.
\(ZnCl_{2}+2H_{2}O\rightleftharpoons Zn\left ( OH \right )_{2}+2HCl\)
(i) State the meaning \(\rightleftharpoons\) of the symbol .[1]
(ii) Choose the pH value which is acidic.
Draw a circle around your chosen answer.[1]
pH 3 pH 7 pH 9 pH 14
(e) A compound of zinc has the formula ZnC4H10.
Complete the table to calculate the relative molecular mass of ZnC4H10.
relative molecular mass = [2] [Total: 13]
▶️ Answer/Explanation
(a) Ans: Any three of:
- Good conductors of electricity (due to delocalized electrons)
- Malleable (atoms can slide over each other without breaking bonds)
- High melting and boiling points (strong metallic bonds)
- Shiny/lustrous surface (reflects light well)
- Ductile (can be drawn into wires)
(b) Ans: 3Zn + 2P → Zn3P2
Balancing the equation requires 3 zinc atoms (left) to match Zn3 (right), and 2 phosphorus atoms (left) to match P2 (right).
(c)(i) Ans: 
The anode (positive electrode) should be connected to the positive terminal of the power source.
(c)(ii) Ans:
Positive electrode: Chlorine gas (Cl2)
Negative electrode: Zinc metal (Zn)
In molten ZnCl2, Zn2+ ions are reduced at the cathode, while Cl– ions are oxidized at the anode.
(d)(i) Ans: Reversible reaction
The double arrow indicates the reaction can proceed in both forward and reverse directions.
(d)(ii) Ans: pH 3
Acidic solutions have pH < 7. The reaction produces HCl, a strong acid.
(e) Ans: 123
Calculation: Zn (65) + C (4×12=48) + H (10×1=10) = 65 + 48 + 10 = 123
The relative molecular mass is the sum of atomic masses of all atoms in the formula.