AS & A Level Chemistry - 9701 Paper 4 2013 Summer Zone 1

(a) What is meant by the term standard electrode potential, SEP?
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[Image of question part (a)]

(b) Draw a fully labelled diagram of the apparatus you could use to measure the SEP of the $\text{Fe}^{3+}/\text{Fe}^{2+}$ electrode.
[Image of question part (b)]

(c) The reaction between $\text{Fe}^{3+}$ ions and $\text{I}^-$ ions is an equilibrium reaction.
$$2\text{Fe}^{3+}(\text{aq}) + 2\text{I}^-(\text{aq}) \rightleftharpoons 2\text{Fe}^{2+}(\text{aq}) + \text{I}_2(\text{aq})$$
(i) Use the \textit{Data Booklet} to calculate the $E^\circ_{\text{cell}}$ for this reaction.
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(ii) Hence state, with a reason, whether there will be more products or more reactants at equilibrium.
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(iii) Write the expression for $K_c$ for this reaction, and state its units.
$K_c =$ units ...........................................[Image of question part (c)(iii)]
An experiment was carried out using solutions of $\text{Fe}^{3+}(\text{aq})$ and $\text{I}^-(\text{aq})$ of equal concentrations. 100 cm$^3$ of each solution were mixed together, and allowed to reach equilibrium. The concentrations at equilibrium of $\text{Fe}^{3+}(\text{aq})$ and $\text{I}_2(\text{aq})$ were as follows.
[$\text{Fe}^{3+}(\text{aq})$] = $2.0 \times 10^{-4}$ mol dm$^{-3}$
[$\text{I}_2(\text{aq})$] = $1.0 \times 10^{-2}$ mol dm$^{-3}$
(iv) Use these data, together with the equation given in (c), to calculate the concentrations of $\text{Fe}^{2+}(\text{aq})$ and $\text{I}^-(\text{aq})$ at equilibrium.
[$\text{Fe}^{2+}(\text{aq})$] = ................................... mol dm$^{-3}$
[$\text{I}^-(\text{aq})$] = ................................... mol dm$^{-3}$
(v) Calculate the $K_c$ for this reaction.
$K_c =$ ..............................................
[Image of question part (c)]

Ethyl ethanoate is hydrolysed slowly by water in the following acid-catalysed reaction.
$$\text{CH}_3\text{CO}_2\text{CH}_2\text{CH}_3 + \text{H}_2\text{O} \xrightarrow{\text{H}^+} \text{CH}_3\text{CO}_2\text{H} + \text{CH}_3\text{CH}_2\text{OH}$$
The concentration of ethyl ethanoate was determined at regular time intervals as the reaction progressed.
Two separate experiments were carried out, with different HCl concentrations.
The following graph shows the results of an experiment using [HCl] = 0.1 mol dm^{-3}.


(a) When the experiment was carried out using [HCl] = 0.2 mol dm^{-3}, the following results were obtained.
[Table_1]

(i) Plot these data on the axes above, and draw a line of best fit.

(ii) Use one of the graphs to show that the reaction is first order with respect to $\text{CH}_3\text{CO}_2\text{CH}_2\text{CH}_3$.
Show all your working, and show clearly any construction lines you draw on the graphs.

(iii) Use the graphs to calculate the order of reaction with respect to HCl.
Show all your working, and show clearly any construction lines you draw on the graphs.

(iv) Write the rate equation for this reaction, and calculate the value of the rate constant.
rate =
[7]

(b) (i) Why is it not possible to determine the order of reaction with respect to water in this experiment?
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(ii) Although $[\text{CH}_3\text{CO}_2\text{CH}_2\text{CH}_3]$ decreases during each experiment, [HCl] remains the same as its initial value.
Why is this?
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[2]

(a) (i) What is meant by the density of a substance?
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(ii) Use data from the Data Booklet to explain why the density of iron is greater than that of calcium.
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(b) In general, reactions of the compounds of transition elements can be classified under one or more of the following headings.
acid-base
ligand exchange
precipitation
redox
Choose the most suitable heading to describe each of the following reactions, by placing a tick (✓) in the appropriate column in the table below.
Only one tick should be placed against each reaction.

[Table_1]
\begin{array}{cccc}\hline \text{reaction} & \text{acid-base} & \text{ligand exchange} & \text{precipitation} & \text{redox} \\ \hline \text{[Cu(H}_2\text{O)}_6]^{2+} + 4\text{NH}_3 \rightarrow [\text{Cu(NH}_3)_4]^{2+} + 6\text{H}_2\text{O} \\ \text{[Cu(H}_2\text{O)}_6]^{2+} + 4\text{HCl} \rightarrow [\text{CuCl}_4]^{2-} + 4\text{H}^{+} + 6\text{H}_2\text{O} \\ \text{2FeCl}_2 + \text{Cl}_2 \rightarrow 2\text{FeCl}_3 \\ \text{[Fe(H}_2\text{O)}_6]^{2+} + 2\text{OH}^{-} \rightarrow \text{Fe(OH)}_2 + 6\text{H}_2\text{O} \\ \text{2Fe(OH)}_2 + \frac{1}{2}\text{O}_2 + \text{H}_2\text{O} \rightarrow \text{2Fe(OH)}_3 \\ \text{CrO}_3 + 2\text{HCl} \rightarrow \text{CrO}_2\text{Cl}_2 + \text{H}_2\text{O} \\ \text{Cr(OH)}_3\text{(OH)}_{3} + \text{OH}^{-} \rightarrow [\text{Cr(H}_2\text{O)}_2(\text{OH})_4]^{-} + \text{H}_2\text{O} \\ \text{[Cr(OH)}_{4}^{-} + \frac{1}{2}\text{H}_2\text{O}_2 + \text{OH}^{-} \rightarrow \text{CrO}_4^{2-} + 4\text{H}_2\text{O} \\ \hline\end{array}

(c) Alloys of aluminium, titanium and vanadium are used in aerospace and marine equipment, and in medicine.
When a powdered sample of one such alloy is heated with an excess of aqueous NaOH, only the aluminium reacts, according to the following equation.
\[ 2\text{Al}(s) + 2\text{OH}^{-}(aq) + 6\text{H}_2\text{O}(l) \rightarrow 2\text{[Al(OH)}_4]^{-}(aq) + 3\text{H}_2(g) \]
Reacting 100 g of alloy in this way produced 8.0 dm³ of hydrogen, measured under room conditions.
Calculate the percentage by mass of aluminium in the alloy.
percentage = ...................... %

Because of the lack of reactivity of the nitrogen molecule, extreme conditions need to be used to synthesise ammonia from nitrogen in the Haber process.
(a) Suggest an explanation for the lack of reactivity of the nitrogen molecule, $N_2$. [1]

(b) Under conditions of high temperature, nitrogen and oxygen react together to give oxides of nitrogen.
(i) Write an equation for a possible reaction between nitrogen and oxygen.
(ii) State two situations, one natural and one as a result of human activities, in which nitrogen and oxygen react together.
(iii) What is the main environmental effect of the presence of nitrogen oxides in the atmosphere? [4]

(c) Describe and explain how the basicities of ethylamine and phenylamine compare to that of ammonia. [4]

(d) Compound $X$ is a useful intermediate in the synthesis of pharmaceuticals. $X$ can be synthesised from chloromethylbenzene according to the following scheme.

(i) What \textit{type of reaction} is each of the following?
step 1 .......................................................
step 2 .......................................................
(ii) Suggest reagents and conditions for
step 1, .......................................................
step 2. .......................................................
(iii) Draw the structures of the intermediates $T$ and $W$ in the boxes above. [6]

(a) A series of experiments is carried out in which the reagent shown at the top of the column of the table is mixed, in turn, with each of the reagents at the side. Complete the following table by writing in each box the formula of any gas produced. Write x in the box if no gas is produced. The first column has been completed as an illustration.

[Table with chemical structures and reagents: Na, KOH(aq), Na2CO3(aq) crossed against H2O, OH (Benzene), CO2H (Benzene), OH (Cyclohexanol)]

(b) Compound C is responsible for the pleasant aroma of apples. It can be prepared from phenol by the following 3-step synthesis.

[Image of reaction sequence: Phenol to Compound A, B, C shown with steps 1, 2, 3]

(i) The only by-product of step 1 is HCl. Suggest the reagent that was used to react with phenol to produce compound A.
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(ii) What type of reaction is occurring in step 2?
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(iii) What reagents and conditions are required for step 3?
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(iv) State the reagent and conditions needed to convert C back to B, the reverse of step 3.
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(c) (i) Either compound A or compound B, or both, react with the following reagents. For each reagent draw the structure of the organic product formed with A, and with B. If no reaction occurs, write 'no reaction' in the relevant box.

[Table with reagents: an excess of Br2(aq), heat with HBr, pass vapour over heated Al2O3, heat with acidified K2Cr2O7, crossed against product with A, product with B]

(ii) Choose one of the above reactions to enable you to distinguish between A and B. State below the observations you would make with each compound.

[Table with columns: reagent, observation with A, observation with B]

There are two important polymerisations that occur within living organisms – protein synthesis and the formation of DNA.
(a) Complete the table placing a tick (✓) in the correct column to indicate in which process each substance could be used.

Modern methods of analysis have had far-reaching effects on a number of branches of science including medicine, forensic science, environmental monitoring and archaeology.

(a) Outline, in simple terms, the technique of DNA fingerprinting.
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[4]

(b) Complete the table by indicating whether the items can be used for DNA fingerprinting. Use a tick (✔) for items which can be used for DNA fingerprinting and a cross (✖) for items which cannot.

[Table_1]

item for testing suitable for DNA fingerprinting
human hair
piece of a flint tool
piece of Iron Age pot
piece of Roman leather

[3]

(c) Various forms of chromatography can be used to separate and analyse mixtures. HPLC (high performance liquid chromatography) can be used to separate each of the following mixtures. State another method of chromatography which would separate each mixture.

insecticides in a sample of water ...............................................................
dyes present in a foodstuff ...............................................................
drug residue in an athlete's urine ...............................................................
[3]

(a) (i) Draw a section of the polymer of propenoic acid showing \textbf{two} repeat units.
[Image of propenoic acid structure]
(ii) By what type of chemical reaction is this polymer formed?
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(iii) By what type of bonding is water held on the polymer?
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(b) For some disposable nappies (diapers), the monomer is a mixture of propenoic acid and sodium propenoate. The properties of the polymer are influenced by the proportion of sodium salt in the monomer mixture.
(i) Suggest and explain how the difference in the structure of this polymer compared to one formed only from propenoic acid might affect the water absorbing properties of the polymer.
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(ii) Suggest a property the polymer should have in order to be used in disposable products.
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(c) A variation on the gel used for disposable nappies (diapers) containing more sodium propenoate has been used to treat soils contaminated by heavy metals such as lead (Pb$^{2+}$) and cadmium (Cd$^{2+}$). Suggest why the gel is effective.
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(d) Another variation on this type of polymer is used in hair gels. In these, the polymer chains are cross-linked by a compound known as pentaerythritol.
[Image of pentaerythritol structure]
(i) By what type of chemical reaction are the cross-links in this polymer formed?
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(ii) It is important that the gel should be easily washed out of hair. What is it about the structure of the polymer that allows this to happen?
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