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WAEC WASSCE Chemistry 2020 past questions and answers

This 2020 WAEC WASSCE Chemistry set has 40 practice questions. Try these 5 free sample questions, tap a question to reveal the answer and explanation. Then practise the whole 2020 set with instant marking.

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Sample WAEC WASSCE Chemistry 2020 questions

1. Which change would increase the rate of reaction between calcium carbonate and dilute hydrochloric acid?
  1. Using powdered calcium carbonate instead of large chips
  2. Using a more dilute acid at the same temperature
  3. Cooling the reaction mixture
  4. Removing the acid while the reaction proceeds

Answer: A. Using powdered calcium carbonate instead of large chips

Powdering calcium carbonate increases its exposed surface area for effective collisions.

2. In the equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g), what is the effect of increasing the pressure at constant temperature?
  1. The equilibrium shifts to the left because the left side has fewer gas molecules.
  2. The equilibrium shifts to the right because the right side has fewer gas molecules.
  3. The equilibrium position does not change because pressure affects only solids.
  4. The equilibrium shifts to the left because the right side has fewer gas molecules.

Answer: B. The equilibrium shifts to the right because the right side has fewer gas molecules.

Higher pressure favors the side with fewer gaseous molecules, which is the ammonia side.

3. A reaction releases heat to its surroundings; what is the sign of its enthalpy change, ΔH?
  1. Positive, because the products contain more heat than the reactants
  2. Zero, because heat is transferred to the surroundings
  3. Negative, because the reacting system loses heat
  4. Positive, because the reacting system loses heat

Answer: C. Negative, because the reacting system loses heat

An exothermic reaction transfers heat out of the system and therefore has a negative enthalpy change.

4. Aqueous copper(II) sulfate is electrolysed using inert electrodes; which substance is deposited at the cathode?
  1. Oxygen
  2. Sulfur
  3. Hydrogen
  4. Copper

Answer: D. Copper

Copper(II) ions gain electrons at the cathode and form copper metal.

5. In a redox reaction, what happens to an oxidizing agent?
  1. It gains electrons and is reduced.
  2. It loses electrons and is oxidized.
  3. It gains oxygen and is reduced only if hydrogen is present.
  4. It donates electrons to the reducing agent and remains unchanged.

Answer: A. It gains electrons and is reduced.

An oxidizing agent accepts electrons from another substance and is itself reduced.

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