AS & A Level Chemistry - 9701 Paper 4 2015 Summer Zone 1

(a) Complete the electronic configurations of the following atoms.
oxygen: $1s^2$...........................................
fluorine: $1s^2$...........................................
[1]

(b) A compound of fluorine and oxygen contains three atoms in each molecule.
(i) Predict its formula.
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(ii) Draw a 'dot-and-cross' diagram to show its bonding.
[1]
(iii) Suggest the shape of this molecule.
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(c) (i) Use $E^\circ$ values from the *Data Booklet* to predict the relative oxidising abilities of fluorine and chlorine.
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(ii) Predict the *type of reaction* that would occur between the interhalogen compound chlorine fluoride, $ClF$, and potassium bromide solution.
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(iii) Construct an equation for this reaction.
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(a) Both chloroalkanes and acyl chlorides react with water, but only acyl chlorides fume in moist air.
(i) State which product causes the fumes in this reaction.
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(ii) Explain why the reactivities of chloroalkanes and acyl chlorides differ.
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(b) Compound R is a useful intermediate in the synthesis of pharmaceutical compounds. It can be made from compound P by the following route.



(i) Suggest structures for the starting material P and the intermediate Q. [2]
(ii) Suggest reagents and conditions for the following steps in the above scheme.
step 1 .........................................................................................................................
step 2 .........................................................................................................................
step 4 ......................................................................................................................... [3]

(a) The mass spectrum of the element magnesium is shown below.
(i) From the mass spectrum, complete the table with the relative abundances of the three isotopes.
[Table_1]
isotope relative abundance
$^{24}Mg$
$^{25}Mg$
$^{26}Mg$ [1]
(ii) Use your values in (i) to calculate the relative atomic mass, $A_r$, of magnesium to two decimal places.
$$A_r \text{(Mg)} = \text{.........................} [1]$$

(b) (i) Describe and explain the trend in the thermal stabilities of the nitrates of the Group II elements down the group.
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When lithium nitrate, $\text{LiNO}_3$, is heated, it readily decomposes giving off a brown gas. This reaction is similar to that which occurs when magnesium nitrate is heated, but it does not occur with other Group I nitrates.
(ii) Suggest an equation for the action of heat on $\text{LiNO}_3$.
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(iii) Suggest why the Group I nitrates other than $\text{LiNO}_3$ do not decompose in this way when heated.
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(a) Silver sulfate, $\text{Ag}_2\text{SO}_4$, is sparingly soluble in water. The concentration of its saturated solution is $2.5 \times 10^{-2} \text{mol dm}^{-3}$ at 298 K.
(i) Write an expression for the solubility product, $K_{sp}$, of $\text{Ag}_2\text{SO}_4$, and state its units.
$$K_{sp} = \text{.....................}\hspace{10mm} \text{units: .....................}$$ \hspace{10mm} [1]
(ii) Calculate the value for $K_{sp}(\text{Ag}_2\text{SO}_4)$ at 298 K.
$$K_{sp} = \text{..............................................}$$
[1]
(b) Using $\text{Ag}_2\text{SO}_4$ as an example, complete the following Hess' Law energy cycle relating the
• lattice energy, $\Delta H^{\circ}_{latt}$,
• enthalpy change of solution, $\Delta H^{\circ}_{sol}$, and
• enthalpy change of hydration, $\Delta H^{\circ}_{hyd}$.
On your diagram:
• include the relevant species in the two empty boxes,
• label each enthalpy change with its appropriate symbol,
• complete the remaining two arrows showing the correct direction of enthalpy change.

[4]

(c) An electrochemical cell is set up as follows.
(i) Use the \textit{Data Booklet} to calculate the value of $E^\circ_{cell}$ under standard conditions, stating which electrode is the positive one.
$$E^\circ_{cell} = \text{................................} \hspace{5mm} \text{positive electrode: .........................}$$ [1]
(ii) How would the actual $E_{cell}$ of the above cell compare to the $E^\circ_{cell}$ under standard conditions? Explain your answer.
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[1]
(iii) How would the $E_{cell}$ of the above cell change, if at all, if a few $\text{cm}^3$ of concentrated $\text{Na}_2\text{SO}_4$(aq) were added to
• the beaker containing $\text{Fe}^{3+}$(aq) + $\text{Fe}^{2+}$(aq),
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• the beaker containing $\text{Ag}_2\text{SO}_4$(aq)?
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[2]
(iv) Explain any changes in $E_{cell}$ you have stated in (iii).
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[1]

(d) Solutions of iron(III) sulfate are acidic due to the following equilibrium.
$$[\text{Fe(H}_2\text{O})_6]^{3+}(\text{aq}) \rightleftharpoons [\text{Fe(H}_2\text{O})_5(\text{OH})]^{2+}(\text{aq}) + \text{H}^{+}(\text{aq}) \hspace{3mm} K_a = 8.9 \times 10^{-4} \text{mol dm}^{-3}$$
Calculate the pH of a 0.1 $\text{mol dm}^{-3}$ solution of iron(III) sulfate, $\text{Fe}_2(\text{SO}_4)_3$.
$$\text{pH} = \text{..........................}$$
[2]

(a) Atoms and ions of elements are made up from the three subatomic particles, protons, electrons and neutrons, in varying amounts.
Complete the following table to show the number of each particle in $^{14}C^{2-}$.

[Table with headers: protons, electrons, neutrons and row: $^{14}C^{2-}$]

(b) Describe the observations you would make during the reactions, if any, of the following chlorides with water. Write equations for any reactions that occur.

$CCl_4$ observation .........................................................................
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equation ..........................................................

$GeCl_4$ observation .........................................................................
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equation ..........................................................

$SnCl_4$ observation ..........................................................................
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equation ..........................................................

(c) Suggest a reason for any difference in the reactivities of the chlorides given in (b).
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(d) Use data from the Data Booklet to explain why an aqueous solution of $SnCl_2$ reacts with $Cl_2(g)$ but an aqueous solution of $PbCl_2$ does not.
Write an equation for the reaction.
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(e) (i) State the relationship between the Faraday constant and the Avogadro constant.
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(ii) When a current of 1.2A was passed through dilute sulfuric acid for 30 minutes, it was found that 130 cm³ of oxygen, measured at 25°C and 1 atm, was collected at the anode. The following reaction takes place.

$2H_2O(l) → 4H^+(aq) + O_2(g) + 4e^-$

Use these data and data from the Data Booklet to calculate a value for the Avogadro constant, $L$, by calculating
• the number of moles of oxygen produced,
• the number of moles of electrons needed for this,
• the number of coulombs passed,
• the number of electrons passed,
• the number of electrons in one mole of electrons $(L)$.

$L = ....................................................$ mol⁻¹

1,3-dimethylbenzene is a useful starting material for several commercially important compounds.
(a) The artificial 'musk ketone', A, is a perfume agent added to many cosmetics and detergents. It is made from 1,3-dimethylbenzene by the following route.

1,3-dimethylbenzene
(i) The only by-product of step 2 is HCl.
Suggest the reagent that was used in this step.
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(ii) Suggest the $\textit{type of reaction}$ that is occurring during both step 2 and step 3.
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(iii) State the reagents and conditions needed for step 3.
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(iv) Suggest the structures of the two products formed when A is reacted with alkaline aqueous iodine.
[2]

1,3-dimethylbenzene is also a starting material for the synthesis of the polymer $\textit{Nomex}$, used in fireproof protective clothing worn by firefighters, military pilots and racing car drivers. The polymer is made from 1,3-dimethylbenzene and 1,3-dinitrobenzene by the following route.

1,3-dimethylbenzene
(i) Draw the structure of one repeat unit of $\textit{Nomex}$ in the box above. [1]
(ii) What $\textit{type of polymer}$ is $\textit{Nomex}$?
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(iii) Suggest the by-product formed during step 3.
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(iv) Suggest reagents and conditions for step 2.
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(v) Suggest how and why the properties of the polymer might change if some of the diamine monomer were replaced with 1,3,5-triaminobenzene.

1,3,5-triaminobenzene
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(a) Long chain alkanes such as 4-methylheptane can be 'cracked' to produce shorter chain hydrocarbons.

(i) State the conditions necessary for this reaction to take place.
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(ii) Suggest the structure of B.

[1]
(iii) Compounds C, D and E are isomers with the molecular formula $C_5H_{10}$.
On heating with concentrated acidified $KMnO_4$,
• compound C gives $CO_2$ and compound F $(C_4H_8O_2)$,
• D and E each give a 1:1 mixture of compounds G $(C_2H_4O_2)$ and H $(C_3H_6O_2)$.
Suggest structures for compounds C - H.

[3]
(iv) Name the type of isomerism shown between D and E.
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(b) Propene, $CH_3CH=CH_2$, reacts with bromine to give 1,2-dibromopropane.
(i) How is this reaction usually carried out?
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(ii) State the $\textit{type of reaction}$ that is occurring here.
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(iii) Draw the mechanism of this reaction, including the structures of any intermediates, and any dipoles, lone pairs and curly arrows to show the movements of electrons.
[2]

Proteins are formed by the polymerisation of amino acids.
(a) (i) State the type of chemical reaction used to form these polymer chains.
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(ii) The amino acids serine and valine can combine together to form a dipeptide.

Draw the skeletal structure of the dipeptide 'val-ser'.
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(iii) Suggest how the type of amino acids in a protein determines its three-dimensional structure.
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(b) Using labelled diagrams or words as appropriate, explain
(i) why a particular enzyme may only catalyse a specific reaction on a specific substrate,
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(ii) how non-competitive inhibition of an enzyme-catalysed reaction can occur.
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(a) DNA fingerprinting has become a very important technique for analysing samples from living or once-living organisms.

(i) After extraction and purification, what is the first step in analysing a sample of DNA?
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[1]

(ii) What can be done to increase the amount of DNA for analysis?
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[1]

(iii) During electrophoresis, it is observed that amino acids can move in \textit{different} directions or not at all, whilst DNA fragments always move in the \textit{same} direction.

Explain these two observations.
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[2]

(iv) DNA fingerprinting can also be useful in archaeology.

Which of the following would \textit{not} be suitable for analysis by DNA fingerprinting?
Put a cross (x) in the appropriate box(es).

a piece of leather from an Egyptian tomb [ ]
a sample of skin from a mummified body [ ]
a fragment of ancient pottery [ ]
a piece of wood from a Roman chariot [ ]
[1]

(b) (i) X-ray crystallography can be used to help analyse the structure of macromolecules.

What does this technique tell us about a particular macromolecule?
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[1]

(ii) Which element will show up most strongly in the X-ray crystallography of a biological polymer of general formula $C_xH_wP_yN_zO_2$? Explain your answer.
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[1]

(c) (i) Explain what is meant by a \textit{partition coefficient}.
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[1]

(ii) The partition coefficient of a particular pesticide between hexane and water is 6.0.
A solution contains 0.0042 g of the pesticide dissolved in 25 cm$^3$ of water. The solution is shaken with 25 cm$^3$ of hexane.

Calculate the mass of pesticide that will be dissolved in the hexane layer at equilibrium.
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[2]

(a) One of the problems associated with using shale gas is its variable composition.
Table 1 shows the percentage composition of shale gas from four different sources J, K, L and M.

source | CH₄ | C₂H_x | C₃H_y | CO₂ | N₂
J | 80.3 | 8.1 | 2.3 | 1.4 | 7.9
K | 82.1 | 14.0 | 3.5 | 0.1 | 0.3
L | 88.0 | 0.8 | 0.7 | 10.4 | 0.1
M | 77.5 | 4.0 | 0.9 | 3.3 | 14.3

In the formulae above, $x$ and $y$ are variables.

Table 1

(i) Draw the structures of three possible compounds with the formula C₃H_y.

[2]

(ii) Which source of shale gas, J, K, L or M, will provide the most energy when burned? Explain your answer.

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(iii) Suggest two methods by which carbon dioxide can be removed from shale gas.

1 ..............................................................................................................................................
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2 ..............................................................................................................................................
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[2]

(b) Table 2 shows a comparison of the relative amounts of pollutants produced when shale gas, fuel oil and coal are burned to produce the same amount of energy.

air pollutant | shale gas | fuel oil | coal
CO₂ | 117 | 164 | 208
CO | 0.040 | 0.033 | 0.208
NO₂ | 0.092 | 0.548 | 0.457
SO₂ | 0.001 | 1.12 | 2.59
particulates | 0.007 | 0.84 | 2.74

Table 2

(i) Suggest why shale gas produces the smallest amount of CO₂.

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(ii) Explain which of the three fuels, shale gas, fuel oil or coal, is the largest contributor to ‘acid rain’.

fuel .................
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[1]
(iii) Suggest a reason why fuel oil and coal produce more NO₂ than shale gas.

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(iv) State one environmental consequence of raised levels of

• CO, ......................................................................................................................
• CO₂, ......................................................................................................................

[2]