O LevelChemistryCambridgeExam Questions3. Stoichiometry3.3 The Mole & the Avogadro Constant

The Mole & the Avogadro Constant (Cambridge O Level Chemistry)

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3.3 The Mole & the Avogadro Constant

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3.3 The Mole & the Avogadro Constant

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11 mark

Which row correctly describes the mole and the value of Avogadro’s constant?

 

one mole of a substance is equal to

 one mole of a substance contains
A the substances relative atomic or molecular mass in grams 6.02 x 1023 atoms, molecules or formula units
B the substances atomic number in grams 12.02 x 1023 atoms, molecules or formula units
C the substances relative atomic or molecular mass in grams 6.02 x 1022 atoms, molecules or formula units
D the substances atomic number in grams 12.02 x 1023 atoms, molecules or formula units

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    21 mark

    The complete combustion of methane produces carbon dioxide and steam.

    CH4(g) + 2 O2(g) → 2 H2O(g) + CO2(g)

    Which statements are about the reaction correct?

    1 The empirical formula of methane is CH4
    2 The number of atoms in 1 mole of methane is 4 x Avogadro’s constant
    3 1 mole of methane produces 72 dm3 of gaseous products at r.t.p
    4 1 mole of methane occupies a volume of 12 dm3 at r.t.p

    • 1, 2 and 3

    • 1 and 2

    • 1 and 3

    • 2 and 4

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    31 mark

    Magnesium carbonate and hydrochloric acid react to produce salt, water and carbon dioxide.

    MgCO3 (s) + 2HCl (aq) → MgCl2 (aq) + H2O (l) + CO2 (g) 

    What is the volume of CO2 produced when 21 g of magnesium carbonate (Mr = 84) reacts completely with excess hydrochloric acid?

    One mole of gas occupies 24.0 dm3 at room temperature and pressure.

    • 4 dm3

    • 8 dm3

    • 6 dm3

    • 2 dm3

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    41 mark

    Calcium carbonate undergoes thermal decomposition at high temperatures to form calcium oxide and carbon dioxide.

    CaCO3 → CaO + CO2

    What mass of calcium oxide (Mr = 56) is formed when 60 g of calcium carbonate (Mr = 100) is completely decomposed?

    • 28 g

    • 18.5 g

    • 60 g

    • 33.6 g

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    11 mark

    What is the concentration in mol dm-3 of a solution of sodium hydroxide that contains 16 g of NaOH in 200 cm3 of distilled water?

    • 2 mol dm-3

    • 2.5 mol cm-3

    • 0.2 mol dm-3

    • 1 mol cm-3

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    21 mark

    A student was given a sample of hydrochloric acid and asked to find its concentration in mol / dm3. She titrated 25 cm3 of the acid against a standard solution of sodium hydroxide of 0.1 mol dm-3. The average titre of sodium hydroxide was 30 cm3.

    What is the concentration of the acid?

    • 0.50 mol dm-3

    • 0.12 mol dm-3

    • 1.25 mol dm-3

    • 1.0 mol dm-3

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    31 mark

    A student thermally decomposes 24.8 g of copper carbonate and obtains 11.2 g of copper(II) oxide and carbon dioxide gas which is released.

    CuCO3 → CuO + CO2

    What is the percentage yield of CuO?

    • 55 %

    • 70 %

    • 82 %

    • 90 %

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    41 mark

    A sample of chalk (limestone) with a mass of 1.70 g was reacted with excess HCl and the amount of carbon dioxide given off was measured using a gas syringe. 0.36 dm3 of CO2 gas was collected at r.t.p.

    CaCO3 + 2HCl → CaCl2 + CO2 + H2O

    What is the percentage purity of the chalk?

    • 75 %

    • 88 %

    • 90 %

    • 98 %

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    51 mark

    A chemist wants to make calcium nitrate. They start with 8.00 g of pure calcium oxide and an excess of dilute nitric acid. They produce 12.65 g of pure, dry anhydrous calcium nitrate crystals.

    What is the percentage yield of calcium nitrate?

    [relative atomic masses, Ar: Ca, 40; N, 14; H, 1; O, 16]

    • 54.0

    • 63.2

    • 67.1

    • 86.8

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    61 mark

    The relative formula masses of four compounds are given.

    A student has a 1.0 g sample of each compound.

    Which sample contains the highest number of moles of oxygen atoms?

     

    compound

    relative formula mass

    A

    Al2O3

    102

    B

    CuO

    80

    C

    H2SO4

    98

    D

    HNO3

    63

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      71 mark

      A compound contains 70% by mass of iron and 30% by mass of oxygen.

      What is its empirical formula? [Ar: O, 16; Fe, 56]

      • FeO

      • Fe2O3

      • Fe3O2

      • Fe3O4

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      81 mark

      25.0 g of hydrated copper(II) sulfate crystals are heated to produce anhydrous copper(II) sulfate and water.

      CuSO4•5H2O(s) → CuSO4(s) + 5H2O(g)

      What is the mass of anhydrous copper(II) sulfate formed?

      [Mr: CuSO4, 160; H2O, 18]

      • 9.0 g

      • 16.0 g

      • 22.5 g

      • 25.0 g

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      91 mark

      The relative formula masses of four compounds are given.

      A student has a 1.0 g sample of each compound.

      Which sample contains the highest number of moles of oxygen atoms?

       

       

      compound

      relative formula mass

      A

      Al2O3

      102

      B

      CuO

      80

      C

      H2SO4

      98

      D

      HNO3

      63

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        101 mark

        50.0 cm3 of 0.10 mol/dm3 silver nitrate, AgNO3, is added to 150.0 cm3 of 0.05 mol/dm3 sodium iodide, NaI, in a beaker.

        After the reaction, solid silver iodide is present in the beaker.

        What else is present?

        • aqueous silver nitrate and aqueous sodium nitrate

        • aqueous sodium iodide and aqueous sodium nitrate

        • aqueous sodium iodide only

        • aqueous sodium nitrate only

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        111 mark

        When 0.1 mol of the hydrocarbon, C5H12, is completely combusted it produces carbon dioxide, CO2, and water, H2O.

        C5H12(l) + 8O2(g) → 5CO2(g) + 6H2O(g)

        What is the volume of carbon dioxide produced when measured at room temperature and pressure?

        • 0.5 dm3

        • 2.4 dm3

        • 5.0 dm3

        • 12 dm3

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        121 mark

        Which compound has the lowest percentage by mass of nitrogen?

        • (NH2)2CO [Mr: 60]

        • (NH4)2SO4 [Mr: 132]

        • (NH4)3PO4 [Mr: 149]

        • NH4NO3 [Mr: 80]

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        11 mark

        Calcium carbide and water react to produce ethyne and calcium hydroxide.

        CaC2 (s) + 2H2O (l) → C2H2 (g) + Ca(OH)2 (s)

        What is the volume of C2H2 produced, at standard temperature and pressure, when 45 g of water reacts completely with calcium carbide?

        • 72 dm3

        • 30 dm3

        • 24 dm3

        • 6 dm3

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        21 mark

        Aluminium and oxygen react to produce aluminium oxide.

        4 Al + 3 O2 → 2 Al2O3

        How many kilograms of aluminium oxide are formed when 5.4 kg of aluminium react with excess oxygen?

        • 5.4 kg

        • 88 kg

        • 10.2 kg

        • 33.6 kg

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        31 mark

        Magnesium nitride and water react to produce a precipitate of magnesium hydroxide and ammonia gas.

        Mg3N2 + 6 H2O → 3 Mg(OH)2 + 2 NH3

        How much magnesium nitride is needed to produce 87 g of the precipitate in excess water?

        • 24 g

        • 50 g

        • 30 g

        • 12 g

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        41 mark

        A student was asked to find the concentration in g / dm3 of a solution of sulfuric acid. She transferred 25 cm3 of the acid to a 250 cm3 volumetric flask and made it up to the mark. She titrated 25 cm3 of the diluted acid against a standard solution of sodium hydroxide of 0.1 mol dm-3. The average titre of sodium hydroxide was 18 cm3.

        What is the concentration of the original acid in grams per decimetre?

        • 9.85 g dm-3

        • 12.25 g dm-3

        • 98 g dm-3

        • 35.28 g dm-3

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        51 mark

        A chemist reacted 0.6 g of magnesium with 0.6 dm3 of oxygen in a sealed container to produce magnesium oxide.

        2Mg + O2 → 2MgO

        Which row correctly describes the limiting reactant?

          limiting reactant reason
        A Mg in excess
        B Mg is used up first
        C O2 is used up first
        D O2 in excess

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