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WAEC WASSCE 2021

WAEC Chemistry 2021 past questions

6 objective questions from the 2021 WAEC Chemistry paper. Answer each one, then reveal the answer and explanation.

All WAEC Chemistry past questions

  1. Question 1

    Mole concept

    How many moles are in 44 g of carbon(IV) oxide? (C = 12, O = 16)

    1. Option A: 0.5
    2. Option B: 1
    3. Option C: 2
    4. Option D: 44
    Show the answer to question 1

    Answer: B, 1

    The molar mass of CO₂ is 12 + 32 = 44 g/mol, so 44 g is 1 mole.

  2. Question 2

    Electronic configuration

    What is the electronic configuration of magnesium (atomic number 12)?

    1. Option A: 2, 8, 1
    2. Option B: 2, 8, 3
    3. Option C: 2, 8, 4
    4. Option D: 2, 8, 2
    Show the answer to question 2

    Answer: D, 2, 8, 2

    Fill the shells in order, 2 then 8 then 8: magnesium has 12 electrons, arranged 2, 8, 2.

  3. Question 3

    Chemical symbols

    What is the chemical symbol of tungsten?

    1. Option A: Tu
    2. Option B: W
    3. Option C: T
    4. Option D: Tn
    Show the answer to question 3

    Answer: B, W

    Tungsten is W, from its other name wolfram.

  4. Question 4

    Organic chemistry

    What is the molecular formula of decane?

    1. Option A: C₁₀H₂₀
    2. Option B: C₁₀H₁₈
    3. Option C: C₁₀H₂₂
    4. Option D: C₁₀H₂₁
    Show the answer to question 4

    Answer: C, C₁₀H₂₂

    Alkanes follow CₙH₂ₙ₊₂, so decane with 10 carbon atoms is C₁₀H₂₂.

  5. Question 5

    Periodic table

    In which group of the periodic table is phosphorus found?

    1. Option A: Group III
    2. Option B: Group V
    3. Option C: Group IV
    4. Option D: Group VI
    Show the answer to question 5

    Answer: B, Group V

    Phosphorus (configuration 2, 8, 5) is in Group V.

  6. Question 6

    Mole concept

    How many moles are there in 75 g of calcium trioxocarbonate(IV) (CaCO₃)? [Ca = 40, C = 12, O = 16]

    1. Option A: 1.5 mol
    2. Option B: 0.38 mol
    3. Option C: 0.75 mol
    4. Option D: 7.5 mol
    Show the answer to question 6

    Answer: C, 0.75 mol

    Moles = mass ÷ molar mass = 75 ÷ 100 = 0.75 mol.

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