Page 51 - ACE YR IGCSE A TOP APPROACH TO CHEM

12 C (ii) Sodium is a very reactive metal. [1]
Steel is used as the core of an overhead cable to prevent
sagging. This is because steel is strong. Aluminium is a (e) MgO + H O [1]
2
better electrical conductor than steel. CuO + CO [1]
2
13 C 3 (a) Zn + 2HCl ➞ ZnCl + H [1]
2
2
Rusting can be prevented by stopping oxygen from (b) Lighted splint [1]
reacting with iron. Attaching copper to the shipʼs hull Pop sound [1]
cannot prevent rusting because copper is less reactive
than iron. Iron will be reduced to form iron ion and react (c) No reaction [1]
with oxygen. Copper metal is unreactive. It cannot react with
14 A dilute hydrochloric acid. [1]
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X can be zinc. Galvanising is a process of coating steel 4 (a) (i) Carbon is more reactive than zinc. [1]
with zinc.
The metal used to coat steel should be more reactive. (ii) Blast / roast in oxygen to react with zinc
The more reactive metal will lose electrons first. The sulfide. [1]
metal is oxidised. 2ZnS + 3O ➞ 2ZnO + 2SO 2
2
Carbon reacts with oxygen. [1]
Part 2: Structured Questions C + O ➞ CO
2 2
1 (a) (i) Z > X > Y > W [1] Carbon dioxide reacts with more carbon.
(ii) Displacement reaction [1] [1]
(iii) Copper [1] CO + C ➞ 2CO
2
Zinc oxide is reduced by CO. [1]
(b) (i) Sodium hydroxide + hydrogen [1] ZnO + CO ➞ Zn + CO
2
(ii) 2Li + 2HCl ➞ 2LiCl + H 2 Calcium carbonate is added to neutralise
Correct formula for products [1] silicon dioxide. [1]
Balanced equation [1] CaCO + SiO ➞ CaSiO + CO
3 2 3 2
(iii) 2Mg + O ➞ 2MgO (iii) Sulfur dioxide [1]
2
Correct formula for product [1] Carbon dioxide [1]
Balanced equation [1] (iv) The temperature in the blast furnace is
(iv) K + Ag [2] higher than the boiling point of zinc. [1]
+
(c) (i) Any two from: [2] (d) (i) Zinc is more reactive than iron. [1]
• Conduct electricity / heat Zinc loses electrons to form zinc ions. [1]
• Malleable / Ductile Zinc ions react with water and oxygen
• Solid at room temperature instead of iron. [1]
(ii) Any three from: [3] (ii) Sacrificial protection [1]
• Chromium can form coloured Magnesium blocks are also commonly used to
compounds, but calcium does not. protect steel ships.
• Chromium has catalytic activity, but (e) Any one from: [1]
calcium does not. • Coins
• Chromium has variable oxidation states, • Musical instruments
but calcium does not. • Doorknobs
• Chromium can form complex ions, but • Ornaments
calcium does not.
• Chromium is less reactive than calcium. (f) Atoms are of different sizes. [1]
(iii) Add sodium hydroxide. [1] The layers of atoms cannot slide over each other
Chromium turned into a grey-green easily. [1]
precipitate. Calcium turned into a white 5 (a) Any one from:
precipitate. [1] Use: Overhead cable [1]
2 (a) Lead(II) oxide [1] Property: Good conductor of electricity /
Nitrogen oxide [1] Ductile [1]
Or
(b) 2Pb(NO ) ➞ 2PbO + 4NO + O 2 Use: Cooking foil [1]
2
3 2
Correct formula for products [1] Property: Resistant to corrosion [1]
Balanced equation [1] Or
(c) Thermal decomposition [1] Use: Drinks cans [1]
Property: Resistant to corrosion / Light [1]
(d) (i) Sodium nitrite + oxygen [2]

Answers 163

Answers.indd 163 3/4/22 3:54 PM