AS & A Level Chemistry - 9701 Paper 2 2020 Summer Zone 2

Gallium is an element in Group 13.
A sample of gallium is analysed using a mass spectrometer. The mass spectrum produced is shown.



(a) Explain what is meant by the term relative atomic mass.
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.................................................................................................................. [2]

(b) Calculate the relative atomic mass of gallium in this sample. Give your answer to 4 significant figures.
Show your working.

relative atomic mass = ........................... [2]

(c) Complete the table which describes a gaseous atom of gallium.

| isotope | nucleon number | total number of electrons in
lowest energy level | type of orbital which
contains the electron in
the highest energy level |
|---------|----------------|-----------------|-------------------|
| $^{71}Ga$ | | | | [3]

(d) When gallium is heated in excess chlorine, gallium trichloride, $GaCl_3$, is made.
Draw the shape of the gallium trichloride molecule and suggest the $Cl-Ga-Cl$ bond angle.

shape of molecule

bond angle .......................................................... [2]

(e) Gallium oxide, $Ga_2O_3$, and aluminium oxide react in the same way with $HCl(aq)$ and with $NaOH(aq)$.

(i) Suggest the equation for the reaction between $Ga_2O_3$ and $HCl(aq)$.
............................................................................................... [1]

(ii) Suggest an equation for the reaction between gallium oxide and $NaOH(aq)$.
............................................................................................... [2]

(a) Write an equation to show the reaction occurring in stage 1.
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(b) Draw a 'dot-and-cross' diagram to show the arrangement of outer electrons in a molecule of ammonia.

(c) (i) In the boxes, give the oxidation numbers of nitrogen in the nitrogen-containing species for the reaction in stage 3.
$$3NO_2 + H_2O \to 2HNO_3 + NO$$
[Image]
(ii) Explain why the reaction in stage 3 is described as a disproportionation reaction. Include reference to transfer of electrons in your answer.
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(d) The release of nitrogen monoxide into the atmosphere causes atmospheric pollution.
State and explain the effect of nitrogen monoxide gas in contact with moist air.
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(e) The nitric acid made in stage 3 can then be reacted with ammonia to form ammonium nitrate.

Stage 3
$$3NO_2 + H_2O \to 2HNO_3 + NO$$
$$NH_3 + HNO_3 \to NH_4NO_3$$
Calculate the volume of nitrogen dioxide, measured at room temperature and pressure, required to make 40 tonnes of ammonium nitrate.
[1 tonne = 1000 kg]
Show your working.
volume of nitrogen dioxide = ..............................

(f) State one use of ammonium nitrate.
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Sucrose, $C_{12}H_{22}O_{11}$, reacts with water to form glucose and fructose in reaction A.



(a) Suggest a name for this type of reaction.
.................................................................................................................................... [1]

(b) Explain in detail, why glucose and fructose are a pair of structural isomers. Your answer should refer specifically to these two molecules.
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.................................................................................................................................... [2]

(c) Reaction A occurs faster in the presence of an enzyme. This is reaction B.

(i) The activation energy for reaction B is $+29 \text{kJ mol}^{-1}$.
Predict a value for the activation energy of reaction A.
.................................................................................................................................... [1]

(ii) The enthalpy change for reaction A is $-14 \text{kJ mol}^{-1}$.
Predict a value for the enthalpy change for reaction B.
.................................................................................................................................... [1]

(iii) Sketch a labelled energy level diagram for reaction B. Use relevant values from (c)(i) and (c)(ii).

[2]

(d) 1.00 g of sucrose, $C_{12}H_{22}O_{11}$, is completely combusted. The heat energy produced is used to increase the temperature of 250 g of water inside a calorimeter from 25.0°C to 40.7°C.

These data can be used to calculate the enthalpy change of combustion of sucrose.

(i) Explain what is meant by the term enthalpy change of combustion of sucrose.
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.................................................................................................................................... [2]

(ii) Use the Data Booklet to calculate the enthalpy change, in $\text{kJ mol}^{-1}$, for the combustion of sucrose. Assume that all of the heat energy produced is transferred to the water. Show your working.

enthalpy change of combustion of sucrose = .................................. $\text{kJ mol}^{-1}$ [3]

(a) An unlabelled bottle contains a straight-chain haloalkane, Q. The molecular formula of Q is C₅H₁₁X, where X is a halogen; bromine, chlorine or iodine.
A test is carried out to identify the halogen present in Q.
A sample of Q is added to NaOH(aq) and warmed. Dilute nitric acid is then added followed by a few drops of aqueous silver nitrate. A cream precipitate is observed.
(i) Suggest the identity of X.
................................................................................................................. [1]
(ii) Write an ionic equation to describe the formation of the cream precipitate. Include state symbols.
................................................................................................................. [1]
(iii) Describe a further test which would confirm the identity of X.
test ..............................................................................................................
expected result ............................................................................................. [2]

(b) The reaction of Q with NaOH(aq) tends to proceed via an S_N2 mechanism.
(i) Suggest the structural formula of the straight-chain halogenoalkane Q.
................................................................................................................. [1]
(ii) Explain why the reaction tends to proceed via an S_N2 mechanism rather than an S_N1 mechanism.
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................................................................................................................. [2]

(c) Two different halogenoalkanes, P and R, both with the molecular formula C₄H₉Cl, are separately dissolved in ethanol and heated under reflux with sodium hydroxide.
The major organic product of each of these reactions is methylpropene.
(i) Name the type of reaction occurring.
................................................................................................................. [1]
(ii) Write an equation, using molecular formulae, to represent the reaction occurring.
................................................................................................................. [1]
(iii) Draw the skeletal formula of methylpropene.
................................................................................................................. [1]
(iv) Give the names of P and R.
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The reaction sequence shows how ethene, $\text{C}_2\text{H}_4$, can be converted into other organic molecules.



(a) Complete the table to give
• the name of the reaction mechanisms of reactions 1 and 6
• the reagents and conditions required for reactions 1, 2 and 6.

[Table_1]
reaction | name of mechanism | name of reagents and conditions
1
2
6

(b) In reaction 3 the organic molecule reacts with HCN and a KCN catalyst.
(i) Complete the diagram to show the mechanism of the reaction occurring. Include all relevant dipoles, lone pairs and curly arrows in your answer.



(ii) Name the functional groups present in the product of reaction 3.
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(c) Draw the structure of the organic molecule \( W \) formed in reaction 4.