AS & A Level Chemistry - 9701 Paper 4 2012 Winter Zone 2

(a) Write down what you would see, and write equations for the reactions that occur, when silicon(IV) chloride and phosphorus(V) chloride are separately mixed with water.

silicon(IV) chloride
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phosphorus(V) chloride
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(b) Iron(III) chloride, FeCl₃, is used to dissolve unwanted copper from printed circuit boards (PCBs) by the following reaction.

$$2FeCl_3(aq) + Cu(s) \rightarrow 2FeCl_2(aq) + CuCl_2(aq)$$

A solution in which $[Fe^{3+}(aq)]$ was originally equal to $1.50 \text{mol dm}^{-3}$ was re-used several times to dissolve copper from the PCBs, and was then titrated as follows.

A $2.50 \text{cm}^3$ sample of the partially-used-up solution was acidified and titrated with $0.0200 \text{mol dm}^{-3} \text{ KMnO}_4$.
This oxidised any FeCl₂ in the solution back to FeCl₃.
It was found that $15.0 \text{cm}^3$ of $\text{KMnO}_4(aq)$ was required to reach the end point.

(i) Construct an ionic equation for the reaction between $\text{Fe}^{2+}$ and $\text{MnO}_4^{-}$ in acid solution.
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(ii) State here the $\text{Fe}^{2+}: \text{MnO}_4^{-}$ ratio from your equation in (i).
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(iii) Calculate the number of moles of $\text{MnO}_4^{-}$ used in the titration.
(iv) Calculate the number of moles of $\text{Fe}^{2+}$ in $2.50 \text{cm}^3$ of the partially-used-up solution.
(v) Calculate the [$\text{Fe}^{2+}$] in the partially-used-up solution.
(vi) Calculate the mass of copper that could still be dissolved by $100 \text{cm}^3$ of the partially-used-up solution.
mass of copper = ................................ g

(c) When $\text{SiCl}_4$ vapour is passed over Si at red heat, $\text{Si}_2\text{Cl}_6$ is formed. $\text{Si}_2\text{Cl}_6$ contains a Si-Si bond.
The reaction of $\text{Si}_2\text{Cl}_6$ and $\text{Cl}_2$ re-forms $\text{SiCl}_4$.
$$\text{Si}_2\text{Cl}_6(g) + \text{Cl}_2(g) \rightarrow 2\text{SiCl}_4(g)$$
Use bond energy data from the Data Booklet to calculate $\Delta H^\circ$ for this reaction.
$$\Delta H^\circ = ..................... \text{kJ mol}^{-1}$$

(d) Calcium forms three calcium silicides, $\text{Ca}_2\text{Si}$, $\text{CaSi}$ and $\text{CaSi}_2$. The first of these reacts with water as follows.
..........$\text{Ca}_2\text{Si}$ + .........$\text{H}_2\text{O}$ $\rightarrow$ .......$\text{Ca(OH)}_2$ + ......$\text{SiO}_2$ + .....$\text{H}_2$
(i) Balance this equation. You may find the use of oxidation numbers helpful.
(ii) During this reaction, state
which element(s) have been oxidised, .................................................................
which element(s) have been reduced. .................................................................

(a) The diagram below shows an incomplete experimental set-up needed to measure the $E_{cell}$ of a cell composed of the standard $\text{Cu}^{2+}/\text{Cu}$ electrode and an $\text{Ag}^+/\text{Ag}$ electrode.

(i) State the chemical composition of
solution A, .........................................................
electrode B. .........................................................
(ii) Complete the diagram to show the whole experimental set-up.

(b) The above cell is not under standard conditions, because the $[\text{Ag}^+]$ in a saturated solution of $\text{AgCl}$ is much less than 1.0 $\text{mol dm}^{-3}$. The $E_{electrode}$ is related to $[\text{Ag}^+]$ by the following equation.
equation 1 $E_{electrode} = E^°_{electrode} + 0.06 \log[\text{Ag}^+]$
(i) Use the Data Booklet to calculate the $E^°_{cell}$ if the cell was operating under standard conditions.

$E^°_{cell} = ....................... \text{V}$

In the above experiment, the $E_{cell}$ was measured at +0.17V.
(ii) Calculate the value of $E_{electrode}$ for the $\text{Ag}^+/\text{Ag}$ electrode in this experiment.
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(iii) Use equation 1 to calculate $[\text{Ag}^+]$ in the saturated solution.
$[\text{Ag}^+] = ....................... \text{mol dm}^{-3}$

(c) (i) Write an expression for $K_{sp}$ of silver sulfate, $\text{Ag}_2\text{SO}_4$, including units.
$K_{sp} = .................................$ units .........................................
Using a similar experimental set-up to that illustrated opposite, it is found that $[\text{Ag}^+]$ in a saturated solution of $\text{Ag}_2\text{SO}_4$ is $1.6 \times 10^{-2} \text{ mol dm}^{-3}$.
(ii) Calculate the value of $K_{sp}$ of silver sulfate.
$K_{sp} = .................................$

(d) Describe how the colours of the silver halides, and their relative solubilities in $\text{NH}_3(\text{aq})$, can be used to distinguish between solutions of the halide ions $\text{Cl}^-$, $\text{Br}^-$ and $\text{I}^-$.
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(e) Describe and explain the trend in the solubilities of the sulfates of the elements in Group II.
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(a) Catalysts can be described as homogeneous or heterogeneous.

(i) What is meant by the terms homogeneous and heterogeneous?
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(ii) By using iron and its compounds as examples, outline the different modes of action of homogeneous and heterogeneous catalysis. Choose one example of each type, and for each example you should
• state what the catalyst is, and whether it is acting as a homogeneous or a heterogeneous catalyst,
• write a balanced equation for the reaction,
• outline how the catalyst you have chosen works to decrease the activation energy.
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(b) The reaction between $\text{SO}_2$, $\text{NO}_2$ and $\text{O}_2$ occurs in two steps.

\[\begin{align*} \text{NO}_2 + \text{SO}_2 &\rightarrow \text{NO} + \text{SO}_3 \quad \Delta H^\circ_1 = -88\text{ kJ mol}^{-1}\\ \text{NO} + \frac{1}{2} \text{O}_2 &\rightarrow \text{NO}_2 \quad \Delta H^\circ_2 = -57\text{ kJ mol}^{-1} \end{align*}\]

The activation energy of the first reaction, $E_{a_1}$, is higher than that of the second reaction, $E_{a_2}$.

Use the axes below to construct a fully-labelled reaction pathway diagram for this reaction, labelling $E_{a_1}$, $E_{a_2}$, $\Delta H^\circ_1$ and $\Delta H^\circ_2$.

(a) Suggest reagents and conditions for reaction 3.
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(b) What \textit{type of reaction} is reaction 4?
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(c) Suggest reagents and conditions for reaction 5.
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(d) Name the functional group in C that has reacted with hot concentrated acidified KMnO_4.
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(e) Suggest the name of the functional group in capsaicin that has reacted in reaction 1.
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(f) Work out structures for compounds C-F and capsaicin, and draw their structural formulae in the boxes opposite. [5]

Compound G is a naturally occurring aromatic compound that is present in raspberries.

(a) Identify the functional groups present in compound G.
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(b) Complete the following table with information about the reactions of the three stated reagents with compound G.
[Table_1]


(c) The dye H can be made from compound G by the route shown below.

(i) Draw the structures of the amine J and the intermediate K in the boxes above.
(ii) Suggest reagents and conditions for
step 1, ..................................................................................................................................................
step 2. .................................................................................................................................................. [5]


(d) Suggest a reaction scheme by which compound G and propanoic acid could be converted into compound L.

Proteins are complex molecules made up from long chains that are folded to give a three-dimensional structure.
(a) Study the table which describes aspects of bonding in proteins. For each description of a bonding type, indicate whether it contributes to the primary, secondary or tertiary structure of a protein.

| bonding type | structure involved |
| ---------------------------------------- | -------------------|
| disulfide bonds between parts of the chain | |
| hydrogen bonds in a β-pleated sheet | |
| ionic bonds between parts of the chain | |
| peptide links between amino acids | |

(b) Explain, with the use of diagrams as appropriate, the difference between competitive and non-competitive inhibition of enzymes.

(c) The diagram shows one strand of DNA. Draw a matching strand showing clearly, with labels, the bonds holding the two strands together. Name the bases in your strand, indicating clearly which base bonds to each base in the strand shown.

names of bases .........................................................................................

DNA fingerprinting has become an important analytical technique, largely due to its use in ‘screening’ crime suspects. It also has a range of applications in modern analysis including determining family links, medicine and archaeology.
(a) (i) DNA fingerprinting uses an analytical technique you have studied. What is the name of that technique? ..............................................................................................
(ii) In order to carry out DNA fingerprinting, the DNA must first be broken down into shorter lengths of polynucleotides. How is this accomplished? .............................................................................................
(iii) What part of the DNA fragments enables them to move in an electric field? .............................................................................................. [3]
(b) The DNA fingerprints shown were obtained from a crime scene. DNA samples were recovered from two rooms in the house where the crime took place. The victim’s DNA and that of two possible suspects were included in the analysis.


(i) Indicate with an X on the diagram, which lines from suspect 1 and from suspect 2 cannot distinguish which of them was present in the house.
(ii) Based on this evidence one suspect was arrested. Which suspect would you expect this to be? Explain your reasoning. ..................................................................................................... [2]
(c) A sample of a liquid, P, was found at the scene of the crime and was analysed using mass spectrometry and NMR spectroscopy.
The mass spectrum has M and M+1 peaks in the ratio of 5.1:0.22 with the M peak at $m/e = 88$.
The NMR spectrum is shown

Use the data to suggest a structure for $P$, explaining your answer. ........................................................................................... structure of $P$ ................................................................ [5]

(a) The raw material for the polymer, lactic acid (2-hydroxypropanoic acid), is formed by the fermentation of corn starch using enzymes from bacteria.
(i) Calcium hydroxide is added to the fermentation tanks to prevent the production of lactic acid from slowing down. Why might high acidity reduce the effectiveness of the enzymes?
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(ii) The structure of lactic acid is shown.

What type of reaction takes place in this polymerisation?
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(b) Lactic acid exists in two stereoisomeric forms. Draw the other form in the box.


(c) One of the reasons PLA has attracted so much attention is that it is biodegradable. This does, however, restrict some potential uses. The simple polymer has a melting point of around 175°C, but softens between 60-80°C. However, its thermoplastic properties enable it to have a range of uses in fibres and in food packaging.
(i) Explain why PLA would not be a suitable packaging material for foods pickled in vinegar.
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(ii) PLA containers are not used for hot drinks. Suggest why.
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(d) Lactic acid can also be co-polymerised with glycolic acid.

(i) Draw a section of the co-polymer showing one repeat unit.
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(ii) Suggest what type(s) of bonding will occur between chains of this co-polymer, indicating the groups involved.
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(iii) Suggest one property in which the co-polymer differs from PLA.
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