AS & A Level Chemistry - 9701 Paper 4 2009 Winter Zone 1

(a) The Group IV oxides $\text{CO}_2$ and $\text{SiO}_2$ differ widely in their physical properties. Describe these differences and explain them in terms of their structure and bonding.
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(b) What are the properties of a \textit{ceramic} material? Why is silicon(IV) oxide very suitable as a component of ceramics?
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(c) Lead(II) oxide reacts with both acids and bases.
(i) What is the name given to oxides that have this property?
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(ii) Write a balanced equation for the reaction between PbO and NaOH.
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(d) Tin forms an oxide, A, that contains the metal in both oxidation states II and IV. The formula of A can be found by the following method.
• A sample of A was dissolved in $\text{H}_2\text{SO}_4$(aq), producing solution B, which was a mixture of tin(II) sulfate and tin(IV) sulfate.
• A 25.0$\text{cm}^3$ sample of solution B was titrated with 0.0200 mol $\text{dm}^{-3}$ $\text{KMnO}_4$. 13.5$\text{cm}^3$ of $\text{KMnO}_4$ was required to reach the end-point.
• Another 25.0$\text{cm}^3$ sample of solution B was stirred with an excess of powdered zinc. This converted all the tin into tin(II). The excess of zinc powder was filtered off and the filtrate was titrated with 0.0200 mol $\text{dm}^{-3}$ $\text{KMnO}_4$, as before. This time 20.3$\text{cm}^3$ of $\text{KMnO}_4$ was required to reach the end-point.
The equation for the reaction occurring during the titration is as follows.
$$ 2\text{MnO}_4^- + 16\text{H}^+ + 5\text{Sn}^{2+} \rightarrow 2\text{Mn}^{2+} + 8\text{H}_2\text{O} + 5\text{Sn}^{4+} $$
(i) Write a balanced equation for the reaction between Zn and $\text{Sn}^{4+}$.
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(ii) Use the \textit{Data Booklet} to calculate the $E^\circ$ values for the reactions between
• Zn and $\text{Sn}^{4+}$, ..........................................................................................
• $\text{MnO}_4^-$ and $\text{Sn}^{2+}$ ..................................................................................
(iii) Use the results of the two titrations to calculate
• the number of moles of $\text{Sn}^{2+}$ in the first titration sample,
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• the number of moles of $\text{Sn}^{2+}$ in the second titration sample.
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(iv) Use the results of your calculation in (iii) to deduce the $\text{Sn}^{2+}/\text{Sn}^{4+}$ ratio in the oxide A, and hence suggest the formula of A.
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(e) A major use of tin is to make ‘tin plate’, which is composed of thin sheets of mild steel electroplated with tin, for use in the manufacture of food and drinks cans. A tin coating of $1.0 \times 10^{-5} \text{m}$ thickness is often used.
(i) Calculate the volume of tin needed to coat a sheet of steel $1.0\text{m} \times 1.0\text{m}$ to this thickness, on one side only.
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(ii) Calculate the number of moles of tin that this volume represents.
[The density of tin is $7.3\text{g cm}^{-3}$]
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(iii) The solution used for electroplating contains $\text{Sn}^{2+}$ ions. Calculate the quantity of electricity in coulombs needed to deposit the amount of tin you calculated in (ii).
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(a) Show by means of an equation what is meant by the lattice energy of calcium chloride.
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(b) Suggest, with an explanation, how the lattice energies of the following salts might compare in magnitude with that of calcium chloride.
(i) calcium fluoride, CaF$_2$
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(ii) calcium sulfide, CaS
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(c) Use the following data, together with additional data from the Data Booklet, to calculate the lattice energy of CaCl$_2$.

\begin{tabular}{|c|c|} \hline standard enthalpy change of formation of CaCl$_2$ & -796 kJ mol$^{-1}$ \\ \hline standard enthalpy change of atomisation of Ca(s) & +178 kJ mol$^{-1}$ \\ \hline electron affinity per mole of chlorine atoms & -349 kJ mol$^{-1}$ \\ \hline \end{tabular}

$$ \text{enthalpy} \uparrow \quad \text{Ca(s)} + \text{Cl$_2$(g)} $$

lattice energy = ..................................................... kJ mol$^{-1}$ [3]

(d) When a solution of CaCl$_2$ is added to a solution of the dicarboxylic acid, malonic acid, the salt calcium malonate is precipitated as a white solid. The solid has the following composition by mass: Ca, 28.2%; C, 25.2%; H, 1.4%; O, 45.2%.

(i) Calculate the empirical formula of calcium malonate from these data.

(ii) Suggest the structural formula of malonic acid. [3]

One major difference between the properties of compounds of the transition elements and those of other compounds is that the compounds of the transition elements are often coloured.
(a) Explain in detail why many transition element compounds are coloured.
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(b) The following graph shows the absorption spectrum of two complexes containing copper.

(i) State the colours of the following complex ions.
[Cu(H2O)6]2+ .................................................................
[Cu(NH3)4(H2O)2]2+ .................................................................
(ii) Using the spectra above give two reasons why the colour of the [Cu(NH3)4(H2O)2]2+ ion is deeper (more intense) than that of the [Cu(H2O)6]2+ ion.
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(iii) Predict the absorption spectrum of the complex [Cu(NH3)2(H2O)4]2+, and sketch this spectrum on the above graph.

(c) Copper forms a complex with chlorine according to the following equilibrium.
$$\text{Cu}^{2+}(\text{aq}) + 4\text{Cl}^{-}(\text{aq}) \rightleftharpoons [\text{CuCl}_4]^{2-}(\text{aq})$$
(i) Write an expression for the equilibrium constant, $K_c$, for this reaction, stating its units.
$K_c =$ ................................................................. units .................................................................
(ii) The numerical value of $K_c$ is $4.2 \times 10^5$. Calculate the $[[\text{CuCl}_4]^{2-}]/[\text{Cu}^{2+}]$ ratio when $[\text{Cl}^{-}] = 0.20 \text{mol} \text{ dm}^{-3}$.
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Cyclohexanol and phenol are both solids with low melting points that are fairly soluble in water.

(a) Explain why these compounds are more soluble in water than their parent hydrocarbons cyclohexane and benzene.   [2]

(b) Explain why phenol is more acidic than cyclohexanol.   [2]

(c) For each of the following reagents, draw the structural formula of the product obtained for each of the two compounds. If no reaction occurs write no reaction in the box.  [7]

(d) Choose one of the above five reagents that could be used to distinguish between cyclohexanol and phenol. Describe the observations you would make with each compound.   [2]

• reagent
• observation with cyclohexanol
• observation with phenol

(a) (i) Suggest reagents and conditions for

reaction I, ..............................................................................................................
reaction II. ..............................................................................................................

(ii) Draw the structural formula of one repeat unit of Kevlar in the box above.

(b) The di-acid chloride C reacts with a variety of reagents. Suggest the structural formulae of the products of the reaction of C with

(i) $CH_3NH_2$,

(ii) $HOCH_2CH_2OH$.

(c) The diamine D also reacts with a variety of reagents. Suggest the structural formulae of the products of the reaction of D with

(i) $HCl(aq)$,

(ii) $Br_2(aq)$.


(d) 4-aminobenzoic acid, E, is a useful intermediate for making dyes.



Suggest reagents and conditions for

reaction III, ..............................................................................................................
reaction IV. ..............................................................................................................


(e) 4-aminobenzoic acid, E, forms a zwitterion.

(i) What is meant by the term zwitterion?

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(ii) Draw the structural formula of the zwitterion formed from 4-aminobenzoic acid.

(a) The diagram shows part of one strand of DNA. Draw the complementary strand, labelling the bonds formed to the original strand, and labelling the components of the strand you draw.

(b) Briefly describe the roles of each of the following in protein synthesis.
(i) tRNA ........................................................................................................... ........................................................................................................................ ........................................................................................................................
(ii) the ribosome ............................................................................................... ........................................................................................................................ ........................................................................................................................

(c) Some diseases, such as sickle cell anaemia, are caused by a single mutation in the DNA for a particular gene. This causes the haemoglobin produced to change the shape of red blood cells, reducing their efficiency in carrying oxygen.
(i) What is meant by a $\textit{mutation}$?
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(ii) Explain why such a mutation could alter the bonding in haemoglobin.
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This question is about the modern techniques of analysis which may be used to determine molecular structures.

(a) In X-ray crystallography X-rays are diffracted by the electron clouds surrounding individual atoms in the structure.

(i) What useful information is provided by X-ray crystallography?

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(ii) Why cannot hydrogen atoms in a structure be detected by this technique?

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(b) Suggest how structures of complex molecules such as enzymes, derived from X-ray crystallography, can help explain their biochemical behaviour.

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(c) NMR spectroscopy, in contrast to X-ray crystallography, is frequently used to examine protons in organic molecules.

(i) What feature of protons enables their detection by NMR spectroscopy?

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(ii) The NMR spectrum below was obtained from a compound X, $C_xH_yO_z$. In the mass spectrum of the compound, the M : M+1 ratio was found to be 25:2.

Determine the values of x, y and z in the formula of X and deduce a possible structure for the compound, explaining how you arrive at your conclusion.



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Possible structure of X

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1. Conventional batteries produce electrons through a chemical reaction between electrolyte and metal.
2. Chemical reaction in the ‘paper’ battery is between electrolyte and carbon nanotubes.
3. Electrons collect on the negative terminal of a battery.
4. Electrons must flow from the negative terminal, through the external circuit to the positive terminal for the chemical reaction to continue.

(a) From your knowledge of the different structures of carbon, suggest which of these is used to make nanotubes.
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(b) Suggest a property of this structure that makes it suitable for making nanotubes.
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(c) Carbon in its bulk form is brittle like most non-metallic solids. Suggest why the energy storage device described can be rolled into a cylinder.
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(d) Name an example of an ‘ionic liquid electrolyte’ (not a solution).
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In recent years a great deal of research has been carried out into finding different anti-cancer drugs. Tumours, which are often symptoms of cancer, are produced when cells replicate uncontrollably. This in turn is brought about by the replication of DNA in these cells.

Two anti-cancer agents are mechlorethamine and cis-platin. They work by binding to the DNA and preventing replication.