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WA2 Practice Paper: Weighted Assessment 2 — question paper

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QQ/S3CH/WA2

Secondary 3 · Chemistry (G2 / G3)

WA2 Practice Paper

Weighted Assessment 2

Duration: 55 minutes
Total: 40 marks
Name:
Class:
Register No.:
Date:

READ THESE INSTRUCTIONS FIRST

  • Write your name, class and register number in the spaces at the top of this page.
  • Answer all questions.
  • Give numerical answers correct to 3 significant figures unless stated otherwise, with units where a quantity is calculated.
  • Chemical equations should be balanced, with state symbols shown where the question asks for them.
  • The number of marks is given in brackets [ ] at the end of each question or part question.
  • The total number of marks for this paper is shown on its cover.

Original practice material written for the MOE Chemistry syllabus. It is not an official MOE or school examination paper. Chapters 3–5 (atomic structure, chemical bonding and structure, mole concept and stoichiometry).

For Examiner’s Use
Section A/ 10
Section B/ 30
Total/ 40

Section A: Multiple-choice questions[10 marks]

Answer all questions. For each question, write the letter (A, B, C or D) of the correct answer.

  1. 1

    An atom of element Z has 11 protons and 12 neutrons. What is the electronic configuration of Z?

    1. A2.8.3
    2. B2.8.2
    3. C2.8.1
    4. D2.10.1
    ( )
  2. 2

    The atoms ³⁵₁₇X and ³⁷₁₇Y are

    1. Aatoms of different elements
    2. Bisotopes of the same element
    3. Cions of the same element
    4. Dthe same isotope written two ways
    ( )
  3. 3

    How many electrons are present in the Ca²⁺ ion? (proton number of Ca = 20)

    1. A20
    2. B22
    3. C2
    4. D18
    ( )
  4. 4

    Which molecule contains a triple covalent bond?

    1. AN₂
    2. BO₂
    3. CH₂O
    4. DCH₄
    ( )
  5. 5

    Solid potassium chloride does not conduct electricity, but molten potassium chloride does, because melting

    1. Acreates free electrons
    2. Bfrees the ions to move
    3. Cbreaks the ions into atoms
    4. Dlowers the boiling point
    ( )
  6. 6

    Which substance has a giant covalent structure and does not conduct electricity?

    1. Agraphite
    2. Bsodium chloride
    3. Csilicon dioxide
    4. Dcopper
    ( )
  7. 7

    Iodine is a solid at room temperature but melts at only 114 °C. This is because

    1. Athe I—I covalent bonds are weak
    2. Bthe forces between the I₂ molecules are weak
    3. Ciodine atoms share electrons unequally
    4. Diodine has a giant molecular structure
    ( )
  8. 8

    How many moles of carbon dioxide are present in 4.4 g of CO₂? (Mr of CO₂ = 44)

    1. A0.2 mol
    2. B44 mol
    3. C0.01 mol
    4. D0.1 mol
    ( )
  9. 9

    What volume does 0.25 mol of hydrogen occupy at room temperature and pressure? (molar volume = 24 dm³/mol)

    1. A24 dm³
    2. B48 dm³
    3. C6 dm³
    4. D96 dm³
    ( )
  10. 10

    0.05 mol of sodium hydroxide is dissolved in water and made up to 250 cm³ of solution. The concentration is

    1. A0.2 mol/dm³
    2. B0.0125 mol/dm³
    3. C5 mol/dm³
    4. D20 mol/dm³
    ( )

Section B: Structured questions[30 marks]

Answer all questions in the spaces provided. Show all necessary working. Give numerical answers to 3 significant figures where appropriate, with units.

  1. 1

    Element Z has the electronic configuration 2.8.8.2 and a nucleon number of 40.

    1. (a)

      State the group and period of the Periodic Table in which Z is placed.

      [2]
    2. (b)

      Write the formula and charge of the ion that Z forms.

      [1]
    3. (c)

      State the number of neutrons in one atom of Z.

      [1]
    4. (d)

      Explain why all isotopes of Z have identical chemical properties.

      [1]
  2. 2

    Magnesium burns in oxygen to form magnesium oxide, MgO.

    1. (a)

      Describe, in terms of electron transfer, how the ionic bond in MgO forms.

      [3]
    2. (b)

      State two physical properties of MgO that follow from its ionic structure.

      [2]
    3. (c)

      Write the formula of magnesium nitrate.

      [1]
  3. 3

    Diamond, graphite, iodine and silicon dioxide have very different physical properties.

    1. (a)

      Explain why graphite conducts electricity but diamond does not.

      [2]
    2. (b)

      State why graphite is used as a lubricant in locks.

      [1]
    3. (c)

      Explain why iodine has a low melting point while silicon dioxide melts at about 1600 °C.

      [3]
    4. (d)

      Name the type of particles that make up silicon dioxide.

      [1]
  4. 4

    Show your working for each calculation. (Mr: CH₄ = 16; CaCO₃ = 100; Avogadro constant = 6.0 × 10²³ per mol)

    1. (a)

      Calculate the number of moles in 8.0 g of methane, CH₄.

      moles of CH₄ =mol[2]
    2. (b)

      Calculate the mass of 0.25 mol of calcium carbonate, CaCO₃.

      mass =g[2]
    3. (c)

      Calculate the number of molecules in 0.25 mol of carbon dioxide.

      molecules =[2]
  5. 5

    Limestone is mainly calcium carbonate. A student heats 50 g of pure calcium carbonate strongly until there is no further change: CaCO₃ → CaO + CO₂. (Mr: CaCO₃ = 100; CO₂ = 44; molar volume of gas at r.t.p. = 24 dm³/mol)

    1. (a)

      Calculate the moles of calcium carbonate heated.

      moles of CaCO₃ =mol[2]
    2. (b)

      Calculate the mass of carbon dioxide given off.

      mass of CO₂ =g[2]
    3. (c)

      Calculate the volume of carbon dioxide given off, measured at room temperature and pressure.

      volume of CO₂ =dm³[2]

— End of paper —