O LevelChemistryCambridge (CIE)Exam Questions3. Stoichiometry3.3 The Mole & the Avogadro Constant

The Mole & the Avogadro Constant (Cambridge (CIE) O Level Chemistry): Exam Questions

Exam code: 5070

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3.3 The Mole & the Avogadro Constant

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1
1 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

    Choose your answer

    2
    1 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

    Choose your answer

    3
    1 mark

    Substance X was analysed and found to contain 40.00% carbon, 6.67% hydrogen and 53.33% oxygen by mass.

    What is the empirical formula of X?

    • C4H8O4

    • C6H12O8

    • C2H4O2

    • CH2O

    Choose your answer

    4
    1 mark

    A solution of sodium carbonate, Na2CO3, has a concentration of 0.50 mol / dm3.

    What is this concentration in g / dm3?

    [Mr: Na2CO3, 106]

    • 0.0047 g / dm3

    • 53 g / dm3

    • 106 g / dm3

    • 212 g / dm3

    Choose your answer

    5
    1 mark

    One mole of any substance contains 6.02 × 1023 particles.

    How many molecules are there in 2.0 mol of oxygen gas, O2?

    • 3.01 × 1023

    • 6.02 × 1023

    • 1.20 × 1024

    • 2.41 × 1024

    Choose your answer

    6
    1 mark

    A sample of a compound contains 0.20 mol of carbon atoms, 0.40 mol of hydrogen atoms and 0.10 mol of oxygen atoms.

    What is the empirical formula of the compound?

    • CHO

    • CH2O

    • C2H4O

    • C4H8O2

    Choose your answer

    1
    1 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

    Choose your answer

    2
    1 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

    Choose your answer

    3
    1 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 %

    Choose your answer

    4
    1 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 %

    Choose your answer

    5
    1 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

    Choose your answer

    6
    1 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

    Choose your answer

    7
    1 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

    Choose your answer

    8
    1 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

      Choose your answer

      9
      1 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

      Choose your answer

      10
      1 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

      Choose your answer

      11
      1 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]

      Choose your answer

      12
      1 mark

      A substance was analysed and found to contain 26.57 % potassium, 35.36 % chromium, and 38.07 % oxygen by mass.

      What is the empirical formula of the substance?

      • KCr2O7

      • K2CrO7

      • K2Cr2O5

      • K2Cr2O7

      Choose your answer

      13
      1 mark

      Substance X was analysed and found to contain 40.00 % carbon, 6.67 % hydrogen and 53.33 % oxygen by mass. The compound has a relative molecular mass of 60.0 g mol-1.

      What is the molecular formula of X?

      • C4H8O4

      • C6H12O8

      • C2H4O2

      • CH2O

      Choose your answer

      14
      1 mark

      The empirical formula of compound X is CH2 and the relative molecular mass, Mr, of X is 70.

      What is the molecular formula of X?

      • CH2

      • C2H4

      • C5H10 

      • CnH2n

      Choose your answer

      15
      1 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

      Choose your answer

      16
      1 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

      Choose your answer

      1
      1 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 room temperature and pressure, when 45 g of water reacts completely with calcium carbide?

      • 72 dm3

      • 30 dm3

      • 24 dm3

      • 6 dm3

      Choose your answer

      2
      1 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

      Choose your answer

      3
      1 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

      Choose your answer

      4
      1 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

      Choose your answer

      5
      1 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

        Choose your answer

        6
        1 mark

        How many oxygen atoms are there in 10.0 g of magnesium nitrate, Mg(NO3​)2​?

        (The Avogadro constant, L, is 6.02 x 1023 mol−1)

        • 4.07 x 1022

        • 8.14 x 1022

        • 1.22 x 1023

        • 2.44 x 1023

        Choose your answer

        7
        1 mark

        What is the volume of hydrogen gas produced, measured at room temperature and pressure (r.t.p.), when 5.0 g of magnesium reacts with an excess of dilute hydrochloric acid?

        (The volume of one mole of any gas is 24 dm3 at r.t.p.)

        • 0.21 dm3

        • 2.5 dm3

        • 5.0 dm3

        • 120 dm3

        Choose your answer