AS & A Level Chemistry - 9701 Paper 4 2014 Winter Zone 2

(a) The oxidation of nitrogen(II) oxide is shown in the equation.
$$ 2\text{NO}(g) + \text{O}_2(g) \rightarrow 2\text{NO}_2(g) $$
The initial rate of this reaction was measured, starting with different concentrations of the two reactants. The following results were obtained.

[Table]
experiment number | [NO] / mol dm^-3 | [O₂] / mol dm^-3 | initial rate / mol dm^-3 s^-1
1 | 0.032 | 0.012 | 4.08 × 10^-3
2 | 0.032 | 0.024 | 8.15 × 10^-3
3 | 0.064 | 0.024 | 3.28 × 10^-2
4 | 0.096 | 0.036 |

(i) Use the data in the table to determine the order with respect to each reactant. Show your reasoning.
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(ii) Calculate the initial rate in experiment 4. Give your answer to two significant figures.
initial rate = .............................. mol dm^-3 s^-1

(iii) Write the rate equation for this reaction.
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(iv) Use the results of experiment 1 to calculate the rate constant, $k$, for this reaction. Include the units of $k$.
rate constant, $k$ = ........................................ units ..............................


(b) (i) On the following axes
• draw two Boltzmann distribution curves, at two different temperatures, $T_1$ and $T_2$ ($T_2 > T_1$),
• label the curves and the axes.


(ii) State and explain, using your diagram, the effect of increasing temperature on the rate of reaction.
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[5]

(c) The compound nitrosyl fluoride, NOF, can be formed by the following reaction.
$$ 2\text{NO}(g) + \text{F}_2(g) \leftrightarrow 2\text{NOF}(g) $$
The rate is first order with respect to NO and F₂.
The reaction mechanism has two steps.
Suggest equations for the two steps of this mechanism, stating which is the rate determining slower step.
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[2]

(a) Complete the electron configurations for Ni and Ni^{2+}.


(b) The presence of electrons in d orbitals is responsible for the colours of transition element compounds.
(i) The d orbitals in an isolated transition metal atom or ion are all at the same energy level. What term is used to describe orbitals that are at the same energy level?
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(ii) Complete the diagram to show the splitting of the d orbital energy levels in an octahedral complex ion.

(iii) On the axes below, sketch the shapes of one d orbital from the lower energy level and one d orbital from the higher energy level.


(c) The octahedral complex $\text{[Ni(H}_2\text{O)}_6]^{2+}$ is green. Explain the origin of the colour of this complex.
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(d) When NH$_3$(aq) is added to the green solution containing $\text{[Ni(H}_2\text{O)}_6]^{2+}$, a grey-green precipitate, A, is formed. This precipitate dissolves in an excess of NH$_3$(aq) to give a blue-violet solution, B. Suggest formulae for A and B and write equations for the two reactions producing A and B.
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(a) Natural phosphorus consists of one isotope, $^{31} ext{P}$. Chlorine exists naturally as two isotopes, $^{35} ext{Cl}$ and $^{37} ext{Cl}$, in the relative abundance ratio of 3:1.

(i) The mass spectrum of PCl$_3$ contains several peaks corresponding to a number of molecular fragments.
Suggest the isotopic composition of the fragments with the following mass numbers.

[Table 1]
mass number | isotopic composition
101 |
103 |
105 |

(ii) Predict the relative ratios of the peak heights of the three peaks corresponding to these fragments.

(b) Phosphorus reacts with chlorine to form a variety of chlorides.
PCl$_5$ is an example of a compound that exists as two structures depending on the conditions.

2PCl$_5$(g) $\rightleftharpoons$ [PCl$_4$]$^+$[PCl$_6$]$^-$(s)

(i) Draw a 'dot-and-cross' diagram to show the bonding in PCl$_5$. Show the outer electrons only.

(ii) Draw diagrams to suggest the shapes of [PCl$_4$]$^+$ and [PCl$_6$]$^-$.


[PCl$_4$]$^+$
[PCl$_6$]$^-$

(c) (i) Phosphorus(III) oxide, P$_4$O$_6$, contains no P–P or O–O bonds.
In the P$_4$O$_6$ molecule, all oxygen atoms are divalent and all phosphorus atoms are trivalent.
Sketch a structure for P$_4$O$_6$.

(ii) P$_4$O$_6$ can act as a ligand.
What is meant by the term ligand?

(d) Phosphate ions in water can be removed by adding a solution containing Ca$^{2+}$(aq) ions, which form a precipitate of calcium phosphate, Ca$_3$(PO$_4$)$_2$.

(i) Write an expression for the $K_{sp}$ of Ca$_3$(PO$_4$)$_2$.
$K_{sp}$ =

(ii) The solubility of Ca$_3$(PO$_4$)$_2$ is 2.50 $\times 10^{-6}$ mol dm$^{-3}$ at 298 K.
Calculate the solubility product, $K_{sp}$, of Ca$_3$(PO$_4$)$_2$ at this temperature. Include the units.

$K_{sp}$ = .................................................... units ....................................................

(e) (i) What is meant by the term lattice energy?

(ii) Explain why the lattice energy of calcium phosphate is less exothermic than that of magnesium phosphate.

(a) Methylbenzene undergoes electrophilic substitution with nitronium ions, NO_2^+. Nitronium ions are generated by the reaction between concentrated sulfuric acid and concentrated nitric acid.
(i) Construct an equation for the formation of nitronium ions, NO_2^+, by this method.
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(ii) Complete the scheme to show the mechanism for this reaction. Use curly arrows to show the movement of electron pairs.


(b) (i) Describe and explain the relative acidities of chloroethanoic acid and ethanoic acid.
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(ii) Describe and explain the relative acidities of phenol and ethanol.
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(c) Phenyl 2-hydroxybenzoate is an antiseptic.

Complete the following table about the reactions of phenyl 2-hydroxybenzoate with the three reagents.
[Table_1]
| reagent | structure of product(s) | type of reaction |
|---------|-------------------------|------------------|
| Na | | |
| excess Br_2(aq) | | |
| excess hot NaOH(aq) | | |

(a) Organohalogen compounds can undergo hydrolysis.
$$ \text{R–Cl + H}_2\text{O} \rightarrow \text{R–OH + HCl} $$
State the relative rates of hydrolysis of the following compounds.
$$ \text{CH}_3\text{CH}_2\text{CH}_2\text{Cl} \quad \text{CH}_3\text{CH}_2\text{COCl} \quad \text{C}_6\text{H}_5\text{Cl} $$
Explain your answer.
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(b) Aminolaevulinic acid is involved in the synthesis of haemoglobin and chlorophyll.
$$ \text{[Image of Aminolaevulinic Acid]} \text{aminolaevulinic acid} $$
Name the three functional groups in aminolaevulinic acid.
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(c) Aminolaevulinic acid reacts readily with bromoethane.
(i) Show the mechanism of the first step of this reaction on the diagram. Include all necessary curly arrows, lone pairs and relevant dipoles.
$$ \text{[Image of Reaction Mechanism]} \text{H}_3\text{C–CH}_2\text{Br} $$
(ii) Name the mechanism in (c)(i).
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(iii) Identify the non-organic product formed in this reaction.
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(d) Three reactions of aminolaevulinic acid are shown. Draw the structures of the products \text{W, X and Y} in the boxes below.
$$ \text{[Image of Chemical Reaction]} $$

(e) Aminolaevulinic acid can undergo polymerisation.
Draw the structure of the polymer showing two repeat units. The linkages between the monomer units should be shown fully displayed.

(a) A mixture of amino acids can be separated by electrophoresis. During an electrophoresis experiment,
● different amino acids move in different directions,
● different amino acids move at different speeds,
● some amino acids do not move at all.
Explain these observations.

(b) (i) A mixture of amino acids can also be separated by thin-layer chromatography. Identify the mobile and the stationary phases in this type of chromatography.
mobile phase ...................................................
stationary phase ...............................................
(ii) What is the process by which thin-layer chromatography can separate a mixture?

(c) State three structural features of DNA.

(d) Some diseases are caused by a mutation in the DNA base sequence which results in one amino acid being replaced by another during protein synthesis. Suggest what changes in the interactions that form the tertiary structure would result from a mutation that replaced a valine residue with a serine residue.
[Image containing the structures of valine and serine]

(a) Oseltamivir is an antiviral drug that slows the spread of the influenza (flu) virus.

Circle two bonds, each in a different functional group, that could be easily hydrolysed in the body. [2]
(b) Oseltamivir is a chiral drug. This drug is usually taken as a single optical isomer rather than as a mixture of isomers.
Suggest one benefit of taking a drug in this way.
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(c) Oseltamivir is a competitive inhibitor of an enzyme produced by the flu virus.
Explain the meaning of the term \textit{competitive inhibitor} and state how its action could be overcome.
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(d) ATP plays an important role in metabolic reactions in living organisms.

What is the function of ATP in living organisms?
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T is a saturated alcohol. It was analysed by mass spectroscopy and NMR spectroscopy. In the mass spectrum, the molecular ion peak, M, was at an m/e value of 74 and the ratio of the heights of the M and M+1 peaks was 20.4 : 0.9.
(a) (i) Use the ratio of the heights of the M and M+1 peaks to calculate the number of carbon atoms in a molecule of T.
(ii) What is the molecular formula of T?
molecular formula = .......................................

(b) The NMR spectrum of T given below shows four absorptions. The absorption at 1.8 ppm is a multiplet and that at 2.5 ppm is a singlet.
(i) Use this information and your answer to (a)(ii) to deduce the structure of T.
T
(ii) Describe and explain which type of proton is responsible for each of the absorptions.
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(iii) The absorption at 1.8 ppm is a multiplet and that at 2.5 is a singlet. State and explain the splitting patterns of the other absorptions, at 0.9 and 3.4 ppm.
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(iv) Describe and explain how the NMR spectrum of T dissolved in $D_2O$ would differ from the one shown.
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