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WAEC (WASSCE) Chemistry10 questions

WAEC Chemistry practice questions

Ten objective questions in the style of WAEC WASSCE Chemistry: atomic structure, electron configuration, the periodic table, moles, pH, reactions of acids, organic chemistry, redox and separation techniques.

Original questions written by Studoli tutors in the style of the WAEC (WASSCE) exam. They are not official past questions.

  1. Topic: Atomic structure

    1. How many neutrons are in an atom of sodium with mass number 23 and atomic number 11?

    Solution

    B. 12

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

  2. Topic: Atomic structure

    2. What is the electronic configuration of oxygen (atomic number 8)?

    Solution

    B. 2, 6

    • The first shell holds up to 2 electrons.
    • The remaining 6 go into the second shell: 2, 6.

  3. Topic: Periodic table

    3. Which of these is an alkali metal?

    Solution

    C. Potassium

    • Alkali metals are in Group 1.
    • Potassium is in Group 1; calcium is Group 2, aluminium Group 3 and iron is a transition metal.

  4. Topic: Mole concept

    4. What is the molar mass of H₂SO₄? (H = 1, S = 32, O = 16)

    Solution

    C. 98 g/mol

    • (2 × 1) + 32 + (4 × 16).
    • 2 + 32 + 64 = 98 g/mol.

  5. Topic: Mole concept

    5. How many moles are in 4 g of sodium hydroxide, NaOH? (Na = 23, O = 16, H = 1)

    Solution

    A. 0.1 mol

    • Molar mass of NaOH = 23 + 16 + 1 = 40 g/mol.
    • Moles = mass ÷ molar mass = 4 ÷ 40 = 0.1 mol.

  6. Topic: Acids and bases

    6. A solution has a hydrogen ion concentration of 10⁻³ mol/dm³. What is its pH?

    Solution

    B. 3

    • pH = −log₁₀[H⁺].
    • −log₁₀(10⁻³) = 3, so the solution is acidic.

  7. Topic: Acids and bases

    7. Which gas is produced when zinc reacts with dilute hydrochloric acid?

    Solution

    C. Hydrogen

    • Metal + acid gives a salt and hydrogen.
    • Zn + 2HCl gives ZnCl₂ + H₂.

  8. Topic: Organic chemistry

    8. Hydrocarbons with the general formula CₙH₂ₙ₊₂ are called

    Solution

    C. alkanes

    • Alkanes are saturated hydrocarbons with the formula CₙH₂ₙ₊₂, for example methane, CH₄.
    • Alkenes are CₙH₂ₙ and alkynes are CₙH₂ₙ₋₂.

  9. Topic: Redox

    9. In terms of electrons, oxidation is

    Solution

    B. loss of electrons

    • Remember OIL RIG: oxidation is loss, reduction is gain of electrons.

  10. Topic: Separation techniques

    10. Which method is used to obtain pure water from salt solution?

    Solution

    B. Distillation

    • Distillation boils the water off and condenses the vapour back into pure water.
    • The salt stays behind. Filtration cannot remove dissolved salt.
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