Unit 1 – Amount of Substance (2014)
Q1.
 1.12 g of iron reacts with oxygen to form 1.60 g of an oxide of iron. Use relative atomic masses: Fe = 56, O = 16.
What is the formula of this oxide of iron?
   A    FeO5
   B    Fe2O10
   C    Fe3O2
   D    Fe2O3
(Total for question = 1 mark)

Q2.
Oxygen gas, O2, can be converted into ozone, O3, by passing it through an electric discharge.
3O2(g) → 2O3(g)
In an experiment, a volume of 300 cm3 of oxygen was used but only 10% of the oxygen was converted into ozone. All volumes were measured at the same temperature and pressure.
The total volume of gas present at the end of the experiment, in cm3, was
   A    200
   B    210
   C    290
   D    300
(Total for question = 1 mark)

Q3.
 Crude oil is composed mainly of alkanes, which are saturated hydrocarbons.
(a)  (i)  Define the term hydrocarbon.
(1)
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(ii)  State what is meant by the term saturated, as applied to a hydrocarbon.
(1)
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(b)  Crude oil can be separated into fractions.
(i)  What property allows crude oil to be separated by fractional distillation?
(1)
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(ii)  Many chemists are of the opinion that we should use fuels such as biodiesel rather than petrol and diesel.
Suggest one reason to support this opinion.
(1)
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(c)  A molecule of a hydrocarbon, X, can be cracked to form one molecule of pentane, C5H12, and two molecules of ethene only.
(i)  Deduce the molecular formula of X.
(1)

(ii)  Give one reason why cracking reactions are carried out in industry and suggest why high temperatures are used in this process other than to speed up the reaction.
(2)
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(d)  Butane, C4H10, is a hydrocarbon which is used as a fuel. It is a gas under standard conditions.
(i)  Explain what is meant by the term fuel.
(1)
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(ii)  Write an equation for the complete combustion of butane under standard conditions. Include state symbols in your answer.
(2)

(iii)  Write an equation for the incomplete combustion of butane to form carbon monoxide and water only. State symbols are not required.
(1)

(iv)  Under what conditions would you expect incomplete combustion to occur?
(1)
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(e)  Butane can react with bromine, in the presence of ultraviolet radiation, according to the following equation.
C4H10 + Br2 → C4H9Br + HBr
(i)  Calculate the atom economy by mass for the formation of C4H9Br. 
Use the expression

Use the Periodic Table as a source of data.
(2)

Final answer = ........................................................... %

*(ii)  Describe the mechanism of the reaction between butane and bromine that forms the products given in the equation below.
C4H10 + Br2 → C4H9Br + HBr
In your answer you should include
·	equations for each step of the mechanism (curly arrows are not required)
·	the name of each step occurring in the mechanism. 
(7)

  
(Total for question = 21 marks)

Q4.
 The recommended limit for safe exposure to sulfur dioxide in the air is 0.000025%. 
What is this concentration in parts per million, ppm?
   A    25
   B    0.25
   C    0.025
   D    0.0025
(Total for question = 1 mark)

Q5.
 Which of the following observations provides the best evidence for the presence of ionic bonding in an unknown substance?
The substance conducts electricity
   A    in the solid state.
   B    in the solid state and in aqueous solution.
   C    in the solid state and when molten.
   D    when molten but not in the solid state.
(Total for question = 1 mark)

Q6.
 When trichloromethane, CHCl3, reacts with chlorine, the organic product is tetrachloromethane, CCl4. The reaction proceeds by free radical substitution.
The equation for this reaction is
CHCl3 + Cl2 → CCl4 + HCl
(a)  State the essential condition for this reaction to occur at room temperature.
(1)
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(b)  The reaction mechanism involves free radicals. Explain what is meant by the term free radical.
(1)
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(c)  The reaction takes place in a series of steps.
(i)  The initiation step is
Cl2 → 2Cl•
Suggest why this initiation step is more likely than
CHCl3 → CCl3• + H•
(1)
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(ii)  Write equations for the two propagation steps.
(2)
First propagation step

Second propagation step

(iii)  Write an equation for the termination step in which tetrachloromethane is formed.
(1)

(d)  Tetrachloromethane can be manufactured using the by-products of chlorination reactions.
C2Cl6 + Cl2 → 2CCl4
Compare the atom economy of this process with that of the reaction which produces tetrachloromethane from trichloromethane and chlorine. A calculation is not required.
(1)
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 (Total for question = 7 marks)

Q7.
 Which of the following can be determined, for an unknown alkene, using only percentage composition by mass data?
   A    Molecular formula
   B    Empirical (simplest) formula
   C    Both the molecular formula and the empirical (simplest) formula
   D    Structural formula
(Total for question = 1 mark)

Q8.
What is the number of atoms in 2.8 g of ethene, C2H4?
DATA
 ·	The molar mass of C2H4 is 28 g mol−1
·	The Avogadro constant is 6.0 × 1023 mol−1 
   A    1.0 × 1022
   B    6.0 × 1022
   C    1.2 × 1023
   D    3.6 × 1023
(Total for question = 1 mark)

Q9.
In an experiment, 1.226 g of potassium chlorate(V), KClO3, was heated. A mass of 0.320 g of oxygen gas, O2, was collected.
2KClO3(s) → 2KCl(s) + 3O2(g)
Use the molar mass of KClO3 = 122.6 g mol−1 and relative atomic mass O = 16.
The percentage yield of oxygen in this experiment is
   A    17.4%
   B    26.1%
   C    66.7%
   D    100%
 (Total for question = 1 mark)

Q10.
 Nickel is an element in the d-block of the Periodic Table.
(a)  Complete the electronic configuration of a nickel atom using the s, p, d notation.
(1)
1s2 .................................................................................................................... 

(b)  A sample of nickel is made up of three isotopes. The percentage abundances are shown in the table below.

Calculate the relative atomic mass of nickel. Give your answer to two decimal places.
(2)

(c)  Nickel reacts with carbon monoxide, CO, to give the compound nickel carbonyl, Ni(CO)4.
Ni(s) + 4CO(g) → Ni(CO)4(g)
(i)  Calculate the volume of carbon monoxide, in dm3, measured at room temperature and pressure, that is required to react completely with 5.87 g of nickel.
[Relative atomic mass: Ni = 58.7 
Molar volume of a gas = 24 dm3 mol−1 at room temperature and pressure.]
(3)

(ii)  Calculate the number of carbon monoxide molecules present in the volume of gas you have calculated in (c)(i). 
[The Avogadro constant, L = 6.02 × 1023 mol−1]
(1)

(d)  Nickel(II) nitrate, Ni(NO3)2, can be made by several different methods.
Method 1
Nickel(II) oxide, NiO, was reacted with dilute nitric acid according to the equation
NiO(s) + 2HNO3(aq) → Ni(NO3)2(aq) + H2O(l)

(i)  Calculate the volume of 2.00 mol dm−3 dilute nitric acid, in cm3, that was required to exactly neutralize 1.494 g of nickel(II) oxide.
Use the relative atomic masses: Ni = 58.7, O = 16.0
(3)

Method 2
A volume of 25.0 cm3 of 2.00 mol dm−3 nitric acid, HNO3, was transferred to a beaker. Solid nickel(II) carbonate, NiCO3, was added until it was in excess.

(ii)  Why was excess nickel(II) carbonate used?
(1)
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(iii)  Why must the beaker be much larger than the volume of acid used?
(1)
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(iv)  Write a balanced equation for the reaction between nickel(II) carbonate and dilute nitric acid, including state symbols.
(2)

*(v)  For Method 2, describe the practical steps that you would take to obtain pure dry crystals of hydrated nickel(II) nitrate, Ni(NO3)2.6H2O, from a mixture of nickel(II) nitrate solution and unreacted solid nickel(II) carbonate.
(4)
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(Total for question = 18 marks)

Q11.
 In an experiment to make crystals of hydrated copper(II) nitrate, a sample of 5.60 g of copper(II) oxide was added to 50 cm3 of 2.50 mol dm−3 nitric acid. The following reaction occurred.
CuO(s) + 2HNO3(aq) → Cu(NO3)2(aq) + H2O(l)
(a)  Calculate the number of moles of each reactant present, and use this to show that the copper(II) oxide was in excess.
The molar mass of copper(II) oxide, CuO, is 79.5 g mol−1
(3)
Moles of copper(II) oxide added

Moles of nitric acid used

The copper(II) oxide is in excess because
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(b)  The copper(II) nitrate solution was heated gently to concentrate it, and then left to crystallize. The mass of hydrated copper(II) nitrate crystals, Cu(NO3)2.6H2O, obtained was 12.52 g.
Calculate the percentage yield.
The molar mass of Cu(NO3)2.6H2O is 295.6 g mol−1.
(3)

(c)  Give one reason why the percentage yield is less than 100%, even though the nitric acid was completely reacted.
(1)
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*(d)  (i)  The nitrate ion, NO3−, contains both covalent and dative covalent bonds.
What is the difference between these types of bond?
(2)
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(ii)  Complete the dot and cross diagram to show the bonding in the nitrate ion. 
Only the outer electron shells for each atom need to be shown.
Represent the nitrogen electrons with crosses (×), and oxygen electrons with dots, (•). The symbol * on the diagram represents the extra electron giving the ion its charge.
(3)

 (Total for question = 12 marks)

Q12.
 A compound has the following percentage composition by mass.
C 61.0%     H 15.3%     N 23.7%
The empirical formula of the compound is
   A    CH3N
   B    C3H9N
   C    C6H9N2
   D    C8H2N3
(Total for question = 1 mark)

Q13.
 Carbon monoxide and oxygen react together as follows.
2CO(g) + O2(g) → 2CO2(g)
If all volumes of gas are measured at the same temperature and pressure, the volume of carbon dioxide produced after 50 cm3 of carbon monoxide react with 25 cm3 of oxygen is
   A    100 cm3
   B    75 cm3
   C    50 cm3
   D    25 cm3
(Total for question = 1 mark)

Q14.
 Potassium chlorate(V), KClO3, decomposes on heating as follows.
2KClO3(s) → 2KCl(s) + 3O2(g)
What is the maximum volume of oxygen, measured in dm3 at room temperature and pressure, which could be obtained by heating 0.50 mol potassium chlorate(V)?
[Molar volume of a gas = 24 dm3 mol−1 at room temperature and pressure.]
   A    8
   B    18
   C    36
   D    72
(Total for question = 1 mark)