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WAEC (WASSCE) الكيمياء10 أسئلة

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.

أسئلة أصلية كتبها مدرّسو Studoli بأسلوب امتحان WAEC (WASSCE). ليست أسئلة رسمية.

  1. الموضوع: Atomic structure

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

    الحل

    B. 12

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

  2. الموضوع: Atomic structure

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

    الحل

    B. 2, 6

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

  3. الموضوع: Periodic table

    3. Which of these is an alkali metal?

    الحل

    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. الموضوع: Mole concept

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

    الحل

    C. 98 g/mol

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

  5. الموضوع: Mole concept

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

    الحل

    A. 0.1 mol

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

  6. الموضوع: Acids and bases

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

    الحل

    B. 3

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

  7. الموضوع: Acids and bases

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

    الحل

    C. Hydrogen

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

  8. الموضوع: Organic chemistry

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

    الحل

    C. alkanes

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

  9. الموضوع: Redox

    9. In terms of electrons, oxidation is

    الحل

    B. loss of electrons

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

  10. الموضوع: Separation techniques

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

    الحل

    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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