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WAEC WASSCE Chemistry 2002 past questions and answers

This 2002 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 2002 set with instant marking.

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Sample WAEC WASSCE Chemistry 2002 questions

1. An element has two isotopes of mass numbers 35 and 37, with natural abundances of 75% and 25% respectively. What is its relative atomic mass?
  1. 35.5
  2. 36.0
  3. 36.5
  4. 37.0

Answer: A. 35.5

The weighted mean is (35 × 0.75) + (37 × 0.25) = 35.5.

2. Which description best explains the formation of magnesium oxide from magnesium and oxygen?
  1. Magnesium and oxygen share one pair of electrons
  2. Magnesium transfers electrons to oxygen to form oppositely charged ions
  3. Oxygen transfers electrons to magnesium to form neutral atoms
  4. Magnesium and oxygen form a metallic bond

Answer: B. Magnesium transfers electrons to oxygen to form oppositely charged ions

Magnesium loses two electrons and oxygen gains them, producing Mg2+ and O2- ions held by electrostatic attraction.

3. What volume would 0.25 mol of an ideal gas occupy at standard temperature and pressure, given a molar gas volume of 22.4 dm^3 mol^-1?
  1. 2.80 dm^3
  2. 4.48 dm^3
  3. 5.60 dm^3
  4. 22.4 dm^3

Answer: C. 5.60 dm^3

The volume is 0.25 × 22.4 = 5.60 dm^3.

4. A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass. What is its empirical formula?
  1. C2H4O2
  2. C2H2O
  3. CH4O
  4. CH2O

Answer: D. CH2O

For 100 g, the mole ratio is approximately 3.33:6.7:3.33, which simplifies to 1:2:1.

5. A fixed mass of gas occupies 300 cm^3 at 27°C. What volume will it occupy at 127°C if its pressure remains constant?
  1. 400 cm^3
  2. 350 cm^3
  3. 300 cm^3
  4. 200 cm^3

Answer: A. 400 cm^3

At constant pressure, V is proportional to absolute temperature, so V2 = 300 × 400/300 = 400 cm^3.

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