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WAEC WASSCE 2019

WAEC Chemistry 2019 past questions

7 objective questions from the 2019 WAEC Chemistry paper. Answer each one, then reveal the answer and explanation.

All WAEC Chemistry past questions

  1. Question 1

    Atomic structure

    An atom has atomic number 11 and mass number 23. How many neutrons does it have?

    1. Option A: 11
    2. Option B: 12
    3. Option C: 23
    4. Option D: 34
    Show the answer to question 1

    Answer: B, 12

    Neutrons = mass number − atomic number = 23 − 11 = 12.

  2. Question 2

    Periodic table

    In which group of the periodic table is potassium found?

    1. Option A: Group II
    2. Option B: Group III
    3. Option C: Group IV
    4. Option D: Group I
    Show the answer to question 2

    Answer: D, Group I

    Potassium (configuration 2, 8, 8, 1) is in Group I.

  3. Question 3

    Mole concept

    How many moles are there in 17.6 g of carbon(IV) oxide (CO₂)? [C = 12, O = 16]

    1. Option A: 0.4 mol
    2. Option B: 0.8 mol
    3. Option C: 0.2 mol
    4. Option D: 4 mol
    Show the answer to question 3

    Answer: A, 0.4 mol

    Moles = mass ÷ molar mass = 17.6 ÷ 44 = 0.4 mol.

  4. Question 4

    Acids, bases and salts

    Which gas is given off when an acid reacts with a trioxocarbonate(IV)?

    1. Option A: Carbon(IV) oxide
    2. Option B: Hydrogen
    3. Option C: Oxygen
    4. Option D: Nitrogen
    Show the answer to question 4

    Answer: A, Carbon(IV) oxide

    Acid + carbonate → salt + water + carbon(IV) oxide.

  5. Question 5

    Gas laws

    A fixed mass of gas occupies 840 cm³ at a pressure of 6 atm. What volume will it occupy at 4 atm if the temperature stays constant?

    1. Option A: 560 cm³
    2. Option B: 1260 cm³
    3. Option C: 840 cm³
    4. Option D: 20160 cm³
    Show the answer to question 5

    Answer: B, 1260 cm³

    By Boyle's law, P₁V₁ = P₂V₂, so V₂ = 6 × 840 ÷ 4 = 1260 cm³.

  6. Question 6

    Electronic configuration

    What is the electronic configuration of calcium (atomic number 20)?

    1. Option A: 2, 8, 8, 1
    2. Option B: 2, 8, 8, 3
    3. Option C: 2, 8, 8, 4
    4. Option D: 2, 8, 8, 2
    Show the answer to question 6

    Answer: D, 2, 8, 8, 2

    Fill the shells in order, 2 then 8 then 8: calcium has 20 electrons, arranged 2, 8, 8, 2.

  7. Question 7

    Chemical symbols

    What is the chemical symbol of gold?

    1. Option A: Au
    2. Option B: Ag
    3. Option C: Go
    4. Option D: Gd
    Show the answer to question 7

    Answer: A, Au

    Gold is Au, from its Latin name aurum.

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