IGCSEChemistryCIETopic Questions3. StoichiometryThe Mole & the Avogadro Constant

The Mole & the Avogadro Constant (CIE IGCSE Chemistry)

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The Mole & the Avogadro Constant

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11 mark

Extended Only

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  6.02 x 1023 atoms, molecules or formula units
C the substances relative atomic or molecular mass in grams  12.04 x 1023 atoms, molecules or formula units
D the substances atomic number in grams  12.04 x 1023 atoms, molecules or formula units



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    21 mark

    Extended Only

    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

    Extended Only

    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

    Extended Only

    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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    51 mark

    Separate: Chemistry and Extended Only

    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

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    11 mark

    Separate: Chemistry and Extended Only

    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

    Separate: Chemistry and Extended Only

    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

    Separate: Chemistry and Extended Only

    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

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    41 mark

    Separate: Chemistry and Extended Only

    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

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    51 mark

    Separate: Chemistry and Extended Only

    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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    61 mark

    Separate: Chemistry and Extended Only

    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 + 2 HCl → CaCl2 + CO2 + H2O

    What is the percentage purity of the chalk?

    • 75 %

    • 88 %

    • 90 %

    • 98 %

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    11 mark

    Extended Only

    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

    Extended Only

    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

    Extended Only

    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

    Separate: Chemistry and Extended Only

    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

    Extended Only

    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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