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1.
Consider the following graph of ln k against
1
(temperature in Kelvin) for the second order
T
decomposition of N2O into N2 and O.
N2O → N2 + O
1
/ 10 3 K–1
T
(a)
State how the rate constant, k varies with temperature, T.
(1)
(b)
Determine the activation energy, Ea, for this reaction.
(3)
(c)
The rate expression for this reaction is rate = k [N2O]2 and the rate constant is
0.244 dm3 mol–1 s–1 at 750 °C.
A sample of N2O of concentration 0.200 mol dm–3 is allowed to decompose. Calculate
the rate when 10 % of the N2O has reacted.
(2)
(Total 6 marks)
2.
(a)
Explain why the relative atomic mass of cobalt is greater than the relative atomic mass of
nickel, even though the atomic number of nickel is greater than the atomic number of
cobalt.
(1)
(b) Deduce the numbers of protons and electrons in the ion Co2+.
(1)
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(c)
Deduce the electron configuration for the ion Co2+.
(1)
(d) Identify a radioactive isotope of cobalt and state one of its uses.
(1)
(Total 4 marks)
3.
Alex and Hannah were asked to investigate the kinetics involved in the iodination of propanone.
They were given the following equation by their teacher.

H ( aq)
CH3COCH3(aq) + I2(aq) 

 CH2ICOCH3(aq) + HI(aq)
Alex’s hypothesis was that the rate will be affected by changing the concentrations of the
propanone and the iodine, as the reaction can happen without a catalyst. Hannah’s hypothesis
was that as the catalyst is involved in the reaction, the concentrations of the propanone, iodine
and the hydrogen ions will all affect the rate.
They carried out several experiments varying the concentration of one of the reactants or the
catalyst while keeping other concentrations and conditions the same, and obtained the results
below.
Composition by volume of mixture / cm3
Experiment
1.00 mol dm–3
CH3COCH3(aq)
Water
1.00 mol dm–3
H+(aq)
5.00 × 10–3
mol dm–3 I2 in KI
Initial rate
/ mol dm–3
s–1
1
10.0
60.0
10.0
20.0
4.96 × 10–6
2
10.0
50.0
10.0
30.0
5.04 × 10–6
3
5.0
65.0
10.0
20.0
2.47 × 10–6
4
10.0
65.0
5.0
20.0
2.51 × 10–6
(a)
Explain why they added water to the mixtures.
(1)
(b) (i)
Deduce the order of reaction for each substance and the rate expression from the
results.
(2)
(ii) Comment on whether Alex’s or Hannah’s hypothesis is correct.
(1)
(c)
Using the data from Experiment 1, determine the concentration of the substances used
and the rate constant for the reaction including its units.
(3)
(d)
(i)
This reaction uses a catalyst. Sketch and annotate the Maxwell-Boltzmann energy
distribution curve for a reaction with and without a catalyst on labelled axes below.
(3)
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(ii)
Describe how a catalyst works.
(1)
(Total 11 marks)
4.
A table of standard electrode potentials can be found in Table 14 of the Data Booklet.
(a)
Describe the materials and conditions used in the standard hydrogen electrode.
(5)
(b)
Define the term oxidizing agent in terms of electron transfer and identify the strongest
oxidizing agent in Table 14 of the Data Booklet.
(2)
(c)
A cell was set up using tin in tin(II) sulfate solution and copper in copper(II) sulfate
solution, with both solutions under standard conditions.
(i)
Calculate the cell potential.
(1)
(ii) Write an equation for the spontaneous cell reaction.
(2)
(Total 10 marks)
5.
(a)
(i)
Draw the shape of the pz orbital using the coordinates shown.
(1)
(ii)
State the electron configuration of Fe3+.
(1)
(iii) Define the term ligand.
(1)
(iv)
Explain why the complex [Fe(H2O)6]3+ is coloured.
(3)
(v)
The element selenium (Z = 34) has electrons in the 4s, 3d and 4p orbitals. Draw an
orbital box diagram (arrow-in-box notation) to represent these electrons. (1)
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(Total 7 marks)
6.
(a)
The production of ammonia is an important industrial process.
N2(g) + 3H2(g)
(i)
2NH3(g)
Using the average bond enthalpy values in Table 10 of the Data Booklet, determine
the standard enthalpy change for this reaction.
(3)
(ii)
The standard entropy values, S, at 298 K for N2(g), H2(g) and NH3(g) are 193, 131
and 192 JK–1 mol–1 respectively. Calculate ∆SO for the reaction and with reference
to the equation above, explain the sign of ∆SO.
(4)
(iii)
Calculate ∆GO for the reaction at 298 K.
(1)
(iv)
Describe and explain the effect of increasing temperature on the spontaneity of the
reaction.
(2)
(b)
The reaction used in the production of ammonia is an equilibrium reaction. Outline the
characteristics of a system at equilibrium.
(2)
(c)
Deduce the equilibrium constant expression, Kc, for the production of ammonia.
(1)
(d)
(i)
0.20 mol of N2(g) and 0.20 mol of H2(g) were allowed to reach equilibrium in a
1 dm3 closed container. At equilibrium the concentration of NH3(g) was
0.060 mol dm–3. Determine the equilibrium concentrations of N2(g) and H2(g) and
calculate the value of Kc.
(3)
(ii)
Predict and explain how increasing the temperature will affect the value of Kc.
(2)
(e)
Describe how increasing the pressure affects the yield of ammonia.
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(2)
(f)
In practice, typical conditions used in the Haber process are a temperature of 500 °C and
a pressure of 200 atmospheres. Outline why these conditions are used rather than those
that give the highest yield.
(2)
(g)
A catalyst of iron is used in the Haber process. State and explain how the catalyst affects
Kc and the position of equilibrium.
(3)
(Total 25 marks)
7.
Nitrogen(II) oxide reacts with hydrogen according to the following equation:
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
The table shows how the rate of reaction varies as the concentrations of the reactants are
changed.
(a)
Experiment
Initial [NO] /
mol dm–3
Initial [H2] /
mol dm–3
Initial rate /
mol (N2) dm–3 s–1
1
0.100
0.100
2.53×10–6
2
0.100
0.200
5.05×10–6
3
0.200
0.100
1.01×10–5
4
0.300
0.100
2.28×10–5
Determine the order of reaction with respect to H2 and with respect to NO.
H2 ................................................................................................................................
NO ..............................................................................................................................
(2)
(b)
Write the rate expression for the reaction.
(1)
(c)
Calculate the value for the rate constant, and state its units using the data from
experiment 1.
(2)
(d) A suggested mechanism for this reaction is as follows.
H2 + NO
X
X + NO → Y + H2O
Y + H2 → N2 + H2O
fast step
slow step
fast step
State and explain whether this mechanism agrees with the experimental rate expression in
(b).
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(4)
(e)
Explain why a single step mechanism is unlikely for a reaction of this kind.
(2)
(f)
Deduce and explain how the initial rate of formation of H2O compares with that of N2.
(2)
(Total 13 marks)
8.
(a)
Below are four structural isomers with molecular formula C4H9Br. State the name of
each of the isomers A, B, C and D.
(4)
(b)
(i)
Identify the isomer(s) which will react with aqueous sodium hydroxide almost
exclusively by an SN1 mechanism. State the meaning of the symbols in the term
SN1 mechanism.
(2)
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(ii)
Using the formula RBr to represent a bromoalkane, state an equation for the rate
determining step of this SN1 reaction.
(1)
(iii)
Identify one isomer that will react with aqueous sodium hydroxide almost
exclusively by an SN2 mechanism. Draw the mechanism for this reaction using
curly arrows to represent the movement of electron pairs. Include the structural
formulas of the transition state and the organic product.
(4)
(c)
State and explain how the rates of the reactions in parts (b) (i) and (b) (iii) are affected
when the concentration of the sodium hydroxide is doubled.
(2)
(d)
State and explain how the rate of reaction of 1-bromobutane with sodium hydroxide
compares with that of 1-chlorobutane with sodium hydroxide.
(2)
(e)
Identify the isomer of C4H9Br that can exist as stereoisomers. Outline how a polarimeter
will distinguish between the isomers, and how their physical and chemical properties
compare.
(5)
(f)
(i)
State the type of reaction that occurs when isomer B, CH3CHBrCH2CH3, reacts
with a hot alcoholic solution of sodium hydroxide.
(1)
(ii)
Explain how the reaction in part (f) (i) occurs by drawing the mechanism, using
curly arrows to represent the movement of electron pairs and identify the two
possible organic products.
(4)
(Total 25 marks)
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9.
(a)
The pKa value for propanoic acid is given in Table 15 of the Data Booklet.
(i)
State the equation for the reaction of propanoic acid with water.
(1)
(ii)
Calculate the hydrogen ion concentration (in mol dm–3) of an aqueous solution of
0.100 mol dm–3 propanoic acid.
(2)
(b)
The graph below shows a computer simulation of a titration of 25.0 cm3 of
0.100 mol dm–3 hydrochloric acid with 0.100 mol dm–3 sodium hydroxide and the pH
range of phenol red indicator.
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Sketch the graph that would be obtained for the titration of 25.0 cm3 of 0.100 mol dm–3
propanoic acid with 0.100 mol dm–3 potassium hydroxide using bromophenol blue as an
indicator. (The pH range of bromophenol blue can be found in Table 16 of the Data
Booklet).
(3)
(Total 6 marks)
10.
Existence of isomers leads to diversity of organic compounds.
(a)
Describe what is meant by the term stereoisomers.
(2)
(b)
1,3-dichlorocyclobutane exists as geometrical isomers, a form of stereoisomers.
(i)
Draw and name the two geometrical isomers of 1,3-dichlorocyclobutane.
(2)
(ii)
Identify the isomer with the higher boiling point and explain your reasoning.
(3)
(Total 7 marks)
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