Unit 1 – Amount of Substance (2013)
Q1-7 (Jan 2013), Q8 – 10 (Jun 2013)
Unit 1 - Jan 2013
Q1.
 Which of the following processes has the highest atom economy?
   A     Making poly(ethene) from ethene.
   B     Making ethene from eicosane, C20H42.
   C     Making chloromethane from methane.
   D     Making magnesium chloride from magnesium and hydrochloric acid.
(Total for question = 1 mark)

Q2.
 How many molecules are present in 16 g of oxygen gas, O2(g)?
[Avogadro constant = 6 × 1023 mol−1]
   A     96 × 1023
   B     12 × 1023
   C     6 × 1023
   D     3 × 1023
(Total for question = 1 mark)

Q3.
 When 0.635 g of copper (relative atomic mass, RAM = 63.5) is added to an excess of silver nitrate solution, 2.158 g of silver (RAM = 107.9) form.  The ionic equation for the reaction is
   A     Cu(s)    +  Ag2+(aq)  →  Cu2+(aq) +  Ag(s)
   B     Cu(s)    + Ag+(aq)    →  Cu+(aq)   +  Ag(s)
   C     2Cu(s) +  Ag2+(aq)  →  2Cu+(aq) +  Ag(s)
   D     Cu(s)    +  2Ag+(aq) →  Cu2+(aq)  +  2Ag(s)
(Total for question = 1 mark)

Q4.
 Hydrogen has three isotopes, 1H, known as protium, 2H, deuterium, and 3H, tritium.
(a)  In terms of sub-atomic particles, give the similarities and differences between atoms of these three isotopes of hydrogen.
(3)
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(b)  When a nitrogen atom collides with a high energy neutron, one atom of tritium and one atom of another element are formed.  Complete the equation below.
(1)

(c)  Tritium-deuterium gas, consisting of molecules each containing one deuterium atom and one tritium atom, is used in some nuclear warheads.  Typically, each warhead has about 4.0 g of the gas added.
(i)   Calculate the number of moles of tritium-deuterium in 4.0 g.
(2)

(ii)   Calculate the volume, in cm3, of 4.0 g of tritium-deuterium gas.

        [Molar volume of a gas under these conditions = 24 000 cm3 mol−1]
(1)

(d)  Tritium is not usually included in calculations of the relative atomic mass of hydrogen, because it is radioactive and has a relatively short half-life.
        Calculate the relative atomic mass of hydrogen with the following isotopic composition.  Give your answer to four decimal places.
(2)

(e)  The electronic energy levels in hydrogen are shown below.

(i)   Mark on the energy level diagram, with an arrow, the transition that represents the ionization energy of hydrogen.
(1)
(ii)   In some versions of the Periodic Table, hydrogen is placed in the same group as sodium.  Give the electronic configurations for both a hydrogen atom and a sodium atom, using the s and p notation.
        Use these electronic configurations to suggest why this is a reasonable grouping.
(2)
H
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Na
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*(f)  Which element in the Periodic Table has the highest first ionization energy?  Justify your answer.
(3)
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Q5.
 When aqueous solutions of barium chloride and potassium sulfate are mixed, a white precipitate forms.  The ionic equation for the reaction is
   A     K+(aq)     +    Cl− (aq)     →  KCl(s)
   B     K2+(aq)    +    2Cl− (aq)   →  KCl2(s)
   C     Ba+(aq)    +    SO4− (aq)  →  BaSO4(s)
   D     Ba2+(aq)  +  SO42− (aq)   →  BaSO4(s)
(Total for question = 1 mark)

Q6.
 This question is about the preparation of the alum, potassium aluminium sulfate, KAl(SO4)212H2O.  It is a double salt consisting of potassium ions, aluminium ions and sulfate ions, and water of crystallization.
(a)  The first step of the preparation involves adding an excess of aluminium foil to 10 cm3 of 2 mol dm−3 potassium hydroxide to form potassium aluminate.
The equation for this reaction is

(i)   Write a balanced ionic equation for this reaction.
(1)

(ii)   Calculate the number of moles of potassium hydroxide used.
(1)

(iii)   Hence state the number of moles of aluminium that react with the potassium hydroxide.
(1)

(iv)   Use your answer to (iii) to calculate the mass of aluminium that reacts with the potassium hydroxide. Use the Periodic Table as a source of data.
(1)

(v)   Calculate the total mass of aluminium added to the potassium hydroxide if a 10% excess of aluminium is required.
(1)

(vi)   Identify two hazards in this first step of the preparation.
(2)
Hazard 1
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Hazard 2
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(b)  The second step of the reaction is the addition of a slight excess of 1 mol dm−3 sulfuric acid.
(i)   Balance the following equation for the reaction
(1)

(ii)   Calculate the volume of the 1 mol dm−3 sulfuric acid that reacts with the potassium aluminate.
(1)

(iii)   State how you would show that the acid had been added in excess.
(2)
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*(iv)   State and explain the steps necessary to obtain pure, dry crystals from the mixture.
(4)
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 (v)   Suggest the colour of the crystals.
(1)
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(vi)   Suggest the formula of another metal ion which could form an alum, in combination with potassium and sulfate ions.
(1)
(Total for question = 17 marks)

Q7.
 Nickel(II) sulfate is prepared by adding an excess of nickel(II) carbonate to 0.010 mol of dilute sulfuric acid.

Solid nickel(II) sulfate crystals are produced with a 20% yield.  How many moles of nickel(II) sulfate crystals are obtained?
   A     0.001
   B     0.002
   C     0.010
   D     0.050
(Total for question = 1 mark)

Unit 1 - Jun 2013
Q8.
Crude oil is a complex mixture of hydrocarbons. Initial separation is achieved by fractional distillation of the crude oil. The separate fractions are further refined to produce hydrocarbons such as decane, C10H22.
(a)  Give the general formula of alkanes.
(1)

(b)  Carbon monoxide, CO, is formed during the incomplete combustion of decane.

(i)  Write an equation for the incomplete combustion of decane, forming carbon monoxide and water only.
(1)

(ii)  Explain why incomplete combustion can occur.
(1)
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(c)  'Low-sulfur fuel' is now supplied to petrol stations. The removal of sulfur from diesel and petrol reduces the emission of toxic oxides of sulfur from vehicle exhausts. One such oxide is sulfur dioxide, SO2.
The bonding in sulfur dioxide may be represented as shown below.
O = S → O
Complete the dot and cross diagram below for the SO2 molecule, showing only outer shell electrons. Use dots to represent the oxygen electrons and crosses to represent the sulfur electrons.
(3)

(d)  Another alkane produced from crude oil is heptane, C7H16. The reforming of heptane produces methylcyclohexane and only one other product. A methylcyclohexane molecule is made from a ring of six carbon atoms bonded to a methyl group.
(i)  Use the information given above to give the skeletal formula of methylcyclohexane.
(1)

(ii)  Write a balanced equation, using molecular formulae, for the reforming of heptane into methylcyclohexane and one other product. State symbols are not required.
(1)

(iii)  Suggest a reason why oil companies reform alkanes such as heptane.
(1)
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(e)  Five branched-chain isomers of heptane are shown in the boxes below.

(i)  Give the systematic name of isomer A.
(1)
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(ii)  In the empty boxes above, draw skeletal formulae for two other branched-chain isomers of C7H16, with no side-chain having more than one carbon atom.
(2)

(f)  Butane, C4H10, reacts with chlorine, Cl2, at room temperature and pressure.
C4H10 + Cl2 → C4H9Cl + HCl

(i)  What other condition is essential for this reaction?
(1)
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(ii)  Write an equation for the initiation step of the mechanism for the above reaction. Curly arrows are not required.
(1)

(iii)  State the type of bond fission involved in the initiation step.
(1)
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(iv)  Write equations for the two propagation steps of this mechanism. Curly arrows are not required.
(2)
First propagation step:

Second propagation step:

(v)  Write one equation for a reaction that would terminate this mechanism.
(1)
(Total for Question = 18 marks)
Q9.
Alkenes are unsaturated hydrocarbons. They are used in the industrial production of many organic compounds.
(a)  Add structural formulae to the flowchart below to show the organic product formed in each addition reaction of 2-methylpropene.
(4)

(b)  Suggest a mechanism for the reaction of 2-methylpropene with bromine, Br2(l). Include curly arrows.
(3)

(c)  Ethene, C2H4, was prepared from ethanol, C2H5OH, by the following reaction
C2H5OH → C2H4 + H2O
A chemist reacted 9.2 g of ethanol, C2H5OH, and obtained 4.2 g of ethene.
Calculate the percentage yield of ethene in the reaction.
(2)

(Total for Question = 9 marks)

Q10.
In the ethene molecule, the CC double bond is made up of
   A    two sigma bonds.
   B    one pi bond.
   C    two pi bonds.
   D    one sigma bond and one pi bond.

(Total for Question = 1 mark)