Question 1 · MCQ · Analyse · 1 mark
Choosing a displacement reaction
Reactivity series
Which pair should produce a displacement reaction in aqueous solution under ordinary school-lab conditions?
(A) Copper strip in zinc sulphate
(B) Silver strip in copper sulphate
(C) Zinc strip in copper sulphate
(D) Gold strip in zinc sulphate
Show answer and solution
Answer: (C) Zinc strip in copper sulphate
Worked solution: Zinc lies above copper in the reactivity series and displaces it: Zn + CuSO₄ → ZnSO₄ + Cu. The other listed solid metals are less reactive than the metal ions they would need to displace.
Question 2 · MCQ · Analyse · 1 mark
A conducting salt sample
Ionic compounds
Solid sodium chloride does not conduct electricity, but molten sodium chloride does. What changes on melting?
(A) The ions become mobile.
(B) Electrons are produced by destroying sodium atoms.
(C) The salt becomes a covalent compound.
(D) The ions disappear.
Show answer and solution
Answer: (A) The ions become mobile.
Worked solution: In the solid lattice the ions are fixed in position. In the melt they can move and carry charge.
Question 3 · MCQ · Analyse · 1 mark
A scratched zinc coating
Corrosion prevention
A zinc-coated iron sheet is scratched. Why can nearby zinc still help protect the iron?
(A) Zinc prevents every possible reaction permanently.
(B) Zinc is more reactive and oxidises preferentially.
(C) Zinc is less reactive than iron.
(D) Zinc converts iron into stainless steel.
Show answer and solution
Answer: (B) Zinc is more reactive and oxidises preferentially.
Worked solution: Zinc is more reactive than iron, so it can be oxidised preferentially and provide sacrificial protection while enough zinc remains.
Question 4 · MCQ · Analyse · 1 mark
Selecting an electrical cable
Properties of metals and non-metals
Which combination makes copper suitable for a wire in an ordinary electric cable?
(A) Brittleness and poor conductivity
(B) Low melting point and solubility in water
(C) High reactivity with cold water
(D) Good electrical conductivity and ductility
Show answer and solution
Answer: (D) Good electrical conductivity and ductility
Worked solution: Copper conducts current well and can be drawn into thin wires because it is ductile. Insulation is added separately for safety.
Question 5 · A-R · Analyse · 1 mark
High melting point of salt
Ionic compounds
Assertion (A): Many ionic compounds have high melting points.
Reason (R): Strong electrostatic attractions between oppositely charged ions require considerable energy to overcome.
(a) Both A and R are true, and R correctly explains A.
(b) Both A and R are true, but R does not correctly explain A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show answer and solution
Answer: (A) Both A and R are true, and R correctly explains A.
Worked solution: The ionic lattice is held by strong attractions. Substantial heat is needed to loosen the lattice sufficiently for melting.
Question 6 · A-R · Analyse · 1 mark
Copper and dilute acid
Reactivity series
Assertion (A): Copper readily liberates hydrogen from dilute hydrochloric acid.
Reason (R): Copper lies below hydrogen in the reactivity series.
(a) Both A and R are true, and R correctly explains A.
(b) Both A and R are true, but R does not correctly explain A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show answer and solution
Answer: (D) A is false, but R is true.
Worked solution: Copper is below hydrogen, so it does not normally displace hydrogen from dilute non-oxidising hydrochloric acid.
Question 7 · VSA · Apply · 2 marks
A metal stored under oil
Properties of metals and non-metals
Sodium is stored under kerosene rather than in an open tray. Explain the choice.
Show answer and solution
Answer: Kerosene reduces contact with air and moisture, with which sodium reacts vigorously.
Worked solution: Sodium is highly reactive. Keeping it under a suitable non-reactive oil prevents rapid reaction with oxygen and water vapour.
Question 8 · VSA · Apply · 2 marks
Predicting an ion pair
Ionic compounds
An atom X loses two electrons and an atom Y gains one electron to complete their outer shells. What is the simplest ratio of X ions to Y ions in a neutral compound?
Show answer and solution
Answer: 1:2; the formula is XY₂.
Worked solution: Each X becomes X²⁺ and each Y becomes Y⁻. Two Y⁻ ions balance one X²⁺ ion.
Question 9 · SA · Analyse · 3 marks
Ranking unknown metals
Reactivity series
Metal P displaces Q from Q sulphate solution. Q displaces R from R sulphate solution. R does not displace Q. Rank P, Q and R by reactivity and justify the order.
Show answer and solution
Answer: P > Q > R.
Worked solution: Displacement occurs when the solid metal is more reactive than the metal in the salt. P displacing Q establishes P > Q; Q displacing R establishes Q > R. R failing to displace Q is consistent with that order.
Question 10 · SA · Analyse · 3 marks
Why carbon is not always enough
Extraction of metals
A student proposes extracting both zinc and aluminium by heating their oxides with carbon. Explain why the same method is unsuitable for aluminium and name its usual extraction principle.
Show answer and solution
Answer: Carbon can reduce zinc oxide under suitable conditions, but aluminium oxide is too stable for that method; aluminium is extracted electrolytically.
Worked solution: Aluminium is more reactive than carbon and holds oxygen strongly. Its oxide is reduced by electrolysis of a suitable molten mixture. Metals below carbon, such as zinc, can be obtained by carbon reduction of their oxides.
Question 11 · LA · Analyse · 5 marks
From electron transfer to properties
Ionic compounds
Sodium has electron arrangement 2,8,1 and chlorine 2,8,7. Explain (i) the ion formed by each, (ii) their combining ratio, (iii) the bond formed, (iv) why solid NaCl does not conduct, and (v) why its aqueous solution does.
Show answer and solution
Answer: Na⁺ and Cl⁻; 1:1; ionic bonding; fixed ions in the solid; mobile ions in solution.
Worked solution: Sodium loses one electron and chlorine gains it. Their charges are equal and opposite, giving NaCl. Electrostatic attraction forms an ionic lattice. Fixed lattice ions cannot carry current through solid salt. Dissolving separates the ions so that they move through the solution and carry charge.
Question 12 · Case Study · Analyse · 4 marks
Choosing a coating for a railing
Corrosion prevention
Three identical iron railings are exposed to rain. P is uncoated, Q is painted with an intact coating, and R is coated with zinc but has a small scratch.
Answer the following:
(i) Which railing has no protective coating? [1 mark]
(ii) What is the main role of intact paint on Q? [1 mark]
(iii) Why may R remain protected even near the scratch? [2 marks]
Show answer and solution
Answer: (i) P. (ii) It limits contact with oxygen and water. (iii) More reactive zinc oxidises preferentially and can protect exposed iron.
Worked solution: Uncoated iron has direct access to moisture and oxygen. Paint supplies a physical barrier. Zinc supplies a barrier plus sacrificial protection, so protection can continue at small scratches while sufficient zinc remains.
