Unit 1 – Amount of Substance (2012)
Q1-6 (Jan 2012), Q7 – 13 (Jun 2012)
Unit 1 - Jan 2012
Q1.
(a) An impure sample of sodium hydrogencarbonate, NaHCO3, of mass 0.227 g, was reacted with an excess of hydrochloric acid. The volume of carbon dioxide evolved was measured at room temperature and pressure and found to be 58.4 cm3.

     The molar volume of any gas at the temperature and pressure of the experiment is 24 dm3 mol−1. The molar mass of sodium hydrogencarbonate is 84 g mol−1.
     (i) Calculate the number of moles of carbon dioxide given off.
(1)

     (ii) Calculate the mass of sodium hydrogencarbonate present in the impure sample.
(2)

     (iii) Calculate the percentage purity of the sodium hydrogencarbonate. Give your answer to two significant figures.
(2)

(b) (i) The total error in reading the gas syringe is ±0.4 cm3. Calculate the percentage error in measuring the gas volume of 58.4 cm3.
(1)

     (ii) Suggest why the carbon dioxide should not be collected over water in this experiment.
(1)
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(Total for question = 7 marks)

Q2.
Oxygen can be prepared using several different reactions. Which of those given below has the highest atom economy by mass?

(Total for question = 1 mark)
Q3.
A molecule is
   A      a group of atoms bonded by ionic bonds.
   B      a group of atoms bonded by covalent bonds.
   C      a group of ions bonded by covalent bonds.
   D      a group of atoms bonded by metallic bonds.
(Total for question = 1 mark)

Q4.
(a) On strong heating, calcium carbonate decomposes to calcium oxide and carbon dioxide:

     Owing to the conditions under which the reaction occurs, it is not possible to measure the enthalpy change directly.
     An indirect method employs the enthalpy changes when calcium carbonate and calcium oxide are neutralized with hydrochloric acid.
     (i) Write the equation for the reaction of calcium carbonate with hydrochloric acid.  State symbols are not required.  [ΔH1 is the enthalpy change for this reaction]
(1)
.............................................................................................................................................................................................. ΔH1
     (ii) The reaction of calcium oxide with hydrochloric acid is

          Use the equations in parts (i) and (ii) to complete the Hess's Law cycle below to show how you could calculate the enthalpy change for the decomposition of calcium carbonate, ΔHreaction. Label the arrows in your cycle.
(3)

     (iii) Complete the expression for ΔHreaction in terms of ΔH1 and ΔH2 .
(1)
                ΔHreaction = 
(b) Suggest two reasons why the value obtained by carrying out these two experiments and using the equation gives a value different to the data booklet value for the decomposition reaction of calcium carbonate.
(2)
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(Total for question = 7 marks)

Q5.
The definition of the mole is
   A      the amount of any substance which occupies a volume of 24 dm3 at room temperature and pressure.
   B      the amount of any substance containing the same number of identical entities as there are in exactly 12 g of the carbon-12 isotope.
   C      the number of atoms in exactly 12 g of the carbon-12 isotope.
   D      the number of molecules in exactly 2 g of hydrogen at room temperature and pressure.
(Total for question = 1 mark)

Q6.
The relative atomic mass is defined as
   A      the mass of an atom of an element relative to 1/12 the mass of a carbon-12 atom.
   B      the mass of an atom of an element relative to the mass of a hydrogen atom.
   C      the average mass of an element relative to 1/12 the mass of a carbon atom.
   D      the average mass of an atom of an element relative to 1/12 the mass of a carbon-12 atom.
(Total for question = 1 mark)

Unit 1 - Jun 2012
Q7.
 (a) Give the general formula for the homologous series of alkenes.
(1)
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(b) What is meant by the term unsaturated as applied to alkenes?
(1)
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 (c) (i) Name the alkene below using E-Z nomenclature.

(2)
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     (ii) Suggest why this alkene cannot be named using the cis-trans naming system. 
(1)
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 (d) Give the structural formula of the organic product of the reaction of ethene, CH2CH2, with
     (i) hydrogen.
(1)

     (ii) chlorine.
(1)

     (iii) acidified aqueous potassium manganate.(VII)
(1)

     (iv) bromine water.
(1)

(e) Draw the mechanism for the reaction of propene with hydrogen bromide to give the major product.
(4)

(f) The structure below shows two repeat units of a polymer.

     (i) Give the displayed formulae of two isomeric alkenes, either of which could have given rise to this polymer.
(2)

     (ii) State why the empirical formula of a poly(alkene) is the same as that of the monomer from which it is produced.
(1)
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     (iii) State, with a reason, the atom economy for the production of a poly(alkene) from an alkene.
(1)
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 (Total for question = 17 marks)

Q8.
Which of the following statements is true? The Avogadro constant is the number of
   A   grams of any element which contains 6.02 × 1023 atoms of that element.
   B   atoms contained in one mole of any element.
   C   atoms contained in one mole of any monatomic element.
   D   particles (atoms, molecules or ions) required to make one gram of a substance.
(Total for question = 1 mark)

Q9.
 Which of the following represents the electronic structure of a nitrogen atom?

(Total for question = 1 mark)

Q10.
 Sodium burns in oxygen to give a pale yellow solid X.
(a) (i)  1.73 g of sodium reacts with 1.20 g of oxygen.
           Calculate the empirical formula of X.
(2)

          (ii) The molar mass of X is 78 g mol−1. Give the molecular formula of X.
(1)
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          (iii) Write the equation, including state symbols, for the reaction of sodium with oxygen to produce X.
(2)

          (iv) Calculate the volume of oxygen in dm3 (at room temperature and pressure) which reacts with 1.73 g of sodium. (The molar volume of any gas at room temperature and pressure is 24 dm3 mol−1.)
(2)

          (v) Calculate the number of oxygen molecules that react with 1.73 g of sodium. (The Avogadro constant = 6.02 × 1023 mol−1.)
(1)

(b) If sodium is burnt in air, compound X is not the only product. Suggest why this is so.
(1)
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 (Total for question = 9 marks)

Q11.
 Complete combustion of 50 cm3 of a hydrocarbon vapour gave 350 cm3 of carbon dioxide, both gas volumes being measured at the same temperature and pressure. The formula of the hydrocarbon could be
   A   C8H18
   B   C7H16
   C   C6H14
   D   C5H12
(Total for question = 1 mark)

Q12.
 In which of the following series does the melting temperature of the element increase from left to right?
   A    Li, Na, K
   B    Al, Si, P
   C    Si, P, S
   D    Na, Mg, Al
(Total for question = 1 mark)

Q13.
 A solution contains 66 ppm of a solute. The mass of the solute dissolved in 1 kg of this solution is
   A   66 g
   B   0.66 g
   C   0.066 g
   D   0.000066 g
(Total for question = 1 mark)