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WAEC WASSCE Chemistry 2018 past questions and answers

This 2018 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 2018 set with instant marking.

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Sample WAEC WASSCE Chemistry 2018 questions

1. Across a period from left to right, what generally happens to the atomic radius of the elements?
  1. It decreases because nuclear charge increases while shielding changes little.
  2. It increases because the atoms gain electron shells.
  3. It remains constant because the proton number is unchanged.
  4. It increases because nuclear attraction becomes weaker.

Answer: A. It decreases because nuclear charge increases while shielding changes little.

Across a period, increasing nuclear charge pulls the electrons closer without adding a new occupied shell.

2. A neutral atom of chlorine-35 has atomic number 17; how many protons, electrons and neutrons does it contain, respectively?
  1. 17, 18 and 17
  2. 17, 17 and 18
  3. 18, 17 and 17
  4. 35, 17 and 18

Answer: B. 17, 17 and 18

The atom has 17 protons, 17 electrons because it is neutral, and 35 - 17 = 18 neutrons.

3. Which statement best describes the bond between hydrogen and chlorine in a hydrogen chloride molecule?
  1. A pair of electrons is transferred completely from hydrogen to chlorine.
  2. Both atoms contribute electrons to a mobile metallic electron cloud.
  3. The atoms share a pair of electrons unequally.
  4. The atoms are held together only by weak intermolecular forces.

Answer: C. The atoms share a pair of electrons unequally.

Hydrogen and chlorine form a polar covalent bond by sharing an electron pair that is attracted more strongly by chlorine.

4. A fixed mass of gas occupies a rigid container at 100 kPa and 27°C; what pressure will it exert at 127°C if its volume remains constant?
  1. 75 kPa
  2. 100 kPa
  3. 125 kPa
  4. 133 kPa

Answer: D. 133 kPa

At constant volume, pressure is proportional to kelvin temperature, so P2 = 100 x 400/300 = 133 kPa.

5. How many moles are present in 11.0 g of carbon dioxide, CO2, given that its molar mass is 44.0 g mol-1?
  1. 0.250 mol
  2. 0.500 mol
  3. 2.00 mol
  4. 4.00 mol

Answer: A. 0.250 mol

The amount is mass divided by molar mass, so 11.0/44.0 = 0.250 mol.

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