iGCSE Chemistry 0620 Extended - 12.1 Experimental design- Exam Style Questions Paper 4- New Syllabus
Question
(i) Name the type of bonding in zinc.
(ii) Name the two types of particles held together by the bonding in (a)(i).
(iii) Name the type of particle whose movement allows zinc to conduct electricity.
(i) State the meaning of the term alloy.
(ii) Name the substance that is present in brass, other than zinc.
- An excess of powdered zinc carbonate is added to dilute sulfuric acid.
- Excess zinc carbonate is separated from aqueous zinc sulfate by filtration.
- Aqueous zinc sulfate is heated until a saturated solution is formed.
- The saturated solution is allowed to cool and crystallise.
- The crystals are removed and dried.
(ii) Name the filtrate in step 2.
(iii) Name a compound, other than zinc carbonate, that can be added to dilute sulfuric acid to produce aqueous zinc sulfate in step 1.
(iv) State what is meant by the term saturated solution.
(v) Step 1 is repeated using large pieces of zinc carbonate instead of powdered zinc carbonate.
All other conditions are the same.
The rate of reaction decreases.
Explain why the rate of reaction decreases. Give your answer in terms of particles.
(vi) Hydrated crystals form in step 4.
State what is meant by the term hydrated.
Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 2.7 — Metallic bonding (Part (a))
• Topic 9.3 — Alloys and their properties (Part (b))
• Topic 7.3 — Preparation of salts (Part (c))
• Topic 12.1 — Experimental design (Part (c)(iv))
• Topic 6.2 — Rate of reaction (Part (c)(v))
▶️ Answer/Explanation
(a)(i) Metallic (bonding).
(a)(ii) Positive ions and electrons.
Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a ‘sea’ of delocalised electrons.
(a)(iii) Electrons.
The delocalised electrons are free to move throughout the metal lattice, carrying charge.
(b)(i) A mixture of a metal with other elements.
An alloy is a homogeneous mixture formed by combining a metal with one or more other elements, typically to enhance properties like strength or hardness.
(b)(ii) Copper.
Brass is a common alloy made primarily of copper and zinc.
(c)(i) 1. Solid stops dissolving / disappearing. 2. No more bubbles / fizzing / effervescence on addition of solid.
When the acid is completely neutralised, excess solid zinc carbonate will remain unreacted at the bottom of the beaker.
(c)(ii) Aqueous zinc sulfate.
Filtration separates the solid residue (excess zinc carbonate) from the liquid, which is the aqueous zinc sulfate solution formed in the reaction.
(c)(iii) Zinc oxide OR zinc hydroxide.
Both zinc oxide and zinc hydroxide react with sulfuric acid to produce zinc sulfate and water.
(c)(iv) A solution containing the maximum concentration of a solute dissolved in the solvent at a specified temperature.
At saturation, the rate of dissolving equals the rate of crystallisation, and no more solute will dissolve.
(c)(v) Large pieces have a smaller surface area, so the frequency of collisions between zinc carbonate and acid particles decreases.
Smaller surface area means fewer reactant particles are exposed for collisions per unit time, slowing down the rate of reaction.
(c)(vi) (Crystals that are) chemically combined with water.
Hydrated crystals contain water of crystallisation within their crystal structure, e.g., $\mathrm{ZnSO_4 \cdot 7H_2O}$.