AS & A Level Chemistry - 9701 Paper 2 2020 Summer Zone 1

Gallium is a metal in Group 13 of the Periodic Table.

(a) There are two stable isotopes of gallium, $^{69} ext{Ga}$ and $^{71} ext{Ga}$.

(i) State, with reference to subatomic particles, how the isotopes $^{69} ext{Ga}$ and $^{71} ext{Ga}$ differ from each other.
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(ii) State what further information is needed to calculate the relative atomic mass of gallium.
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(b) Gallium and its compounds show similar properties to aluminium and its compounds. Gallium reacts with excess chlorine to form gallium trichloride.

(i) At 500°C, gallium trichloride is a gas.
Suggest the type of attraction that exists at 500°C
• between atoms within a gallium trichloride molecule
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• between gallium trichloride molecules.
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(ii) When gallium trichloride is cooled a solid, $Ga_2Cl_6$, forms.
Suggest the name of the attraction formed between two gallium trichloride molecules to form $Ga_2Cl_6$.
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(c) Gallium metal reacts rapidly when exposed to air. A white solid layer is formed on its surface.

(i) Suggest an equation to describe the reaction occurring when gallium metal is exposed to air.
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(ii) The table gives the formula of each gallium-containing product formed when gallium oxide reacts separately with hot aqueous hydrochloric acid and hot aqueous sodium hydroxide.

[Table_1]

Give the name of the type of behaviour shown by gallium oxide in these reactions.
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(a) The equation shown in (a)(i) describes the reaction which occurs when aqueous potassium iodide is added to aqueous copper(II) sulfate. A white precipitate of copper(I) iodide forms in a brown solution of iodine and potassium sulfate.

(i) Balance the equation and include state symbols.
......CuSO₄(.....) + ......KI(.....) → ......CuI(.....) + ......I₂(.....) + ......K₂SO₄(.....) [2]

The table gives the oxidation numbers of iodine in the different species in the equation.

[Table_1]

(ii) Deduce the oxidation number of copper in CuSO₄ and CuI.
• oxidation number of copper in CuSO₄ ................................
• oxidation number of copper in CuI ................................... [1]

(iii) Describe the type of reaction shown by the equation in (a)(i). Explain your answer in terms of electron transfer.
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(b) In the reaction described in (a)(i), a student uses 17.43 g of CuSO₄•yH₂O. By further titration of the reaction products the student concludes that the total amount of CuSO₄ in the sample is 0.0982 mol.

Use the Data Booklet to complete the table to calculate the value of y, where y is an integer. Show your working.

[Table_2]

mass of 0.0982 mol CuSO₄ ................................... g
amount of H₂O in 17.43 g of CuSO₄•yH₂O ................................... mol H₂O
value of y y = ................................... [4]

(a) Explain what is meant by the term enthalpy change of formation.
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(b) Complete the Hess' cycle using the values given in the table and hence calculate the enthalpy change, $\Delta H_r$, for this reaction.

Show your working.
[Table_1]
\[ \text{substance} \quad \Delta H_f/\text{kJ mol}^{-1} \]
\( NO_2(g) \quad 34.0 \)
\( H_2O(l) \quad -286 \)
\( HNO_3(l) \quad -173 \)
\( NO(g) \quad 91.1 \)

$3NO_2(g) + H_2O(l) \overset{\Delta H_r}{\rightarrow} 2HNO_3(l) + NO(g)$

$\Delta H_r = \text{.....................} \text{kJ mol}^{-1}$
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(c) Nitrogen and oxygen do not react at normal atmospheric temperatures.
Explain why.
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(d) State one way that nitrogen oxides are produced naturally.
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(e) Nitrogen dioxide, $NO_2$, acts as a homogeneous catalyst in the oxidation of atmospheric sulfur dioxide.

(i) Explain why $NO_2$ is described as a homogeneous catalyst.
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(ii) Write equations which describe the two reactions occurring when $NO_2$ acts as a catalyst in the formation of sulfur trioxide from sulfur dioxide.
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Calcium nitrate, Ca(NO3)2, reacts with ammonia, carbon dioxide and water to form a mixture of ammonium nitrate and calcium carbonate.

Ca(NO3)2 + 2NH3 + CO2 + H2O → 2NH4NO3 + CaCO3

(a) Explain why ammonia is described as a Brønsted-Lowry base in this reaction.
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The product mixture can then be added to soil.

(b) State two reasons why this mixture of products is added to some soils.
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(c) Complete the table to name the shape and give the bond angle of each species.

| name of shape | bond angle/° |
|---------------|-------------|
| CO2 | |
| | |
| NH3 | |
| | |
| H2O | |

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(a) Below is a list of species which can react with organic compounds.
CN^- \,\, \text{HCl} \,\, \text{Cl} \,\, \text{H}_2\text{O} \,\, \text{CO}_3^{2-}
(i) From the list, identify a species which can react with ethane.
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(ii) From the list, identify \textit{two} species which can attack the $\pi$ bond in ethene.
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(iii) From the list, identify a species which can be used to distinguish between solutions of propanoic acid and propan-1-ol. Describe any relevant observations.
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(b) Cl(g) can be made from Cl$_2$(g).
(i) Describe the conditions required for this process.
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(ii) Name this process.
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(c) (i) Name an organic functional group which reacts with a nucleophile in an addition reaction.
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(ii) Name an organic functional group which tends to react with a nucleophile in an $S_N1$ substitution mechanism.
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(d) But-1-ene reacts with steam in the presence of concentrated phosphoric acid to form two isomers of molecular formula C$_4$H$_{10}$O.
Each reaction occurs via a different intermediate ion.
(i) Draw the structure of both intermediate ions.
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(ii) Circle the more stable intermediate ion drawn in (d)(i). Explain your answer.
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2-methylbut-1-ene reacts with acidified manganate(VII) ions, under specific conditions, to produce two organic compounds X and Y. X immediately reacts with the acidified manganate(VII) ions to form carbon dioxide and water. Y has the structural formula CH$_3$CH$_2$COCH$_3$.



(a) Draw the skeletal formula of 2-methylbut-1-ene.
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(b) (i) State the specific conditions required for the acidified manganate(VII) ions to react with 2-methylbut-1-ene in this way.
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(ii) Name the type of reaction occurring to the functional group in 2-methylbut-1-ene in the reaction in (b)(i).
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(c) Draw the structural formula of X.
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(d) Describe a chemical test and the expected observation(s) to confirm the presence of the carbonyl functional group in Y.
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(e) The infra-red spectrum of 2-methylbut-1-ene is shown.

Predict two main differences that would be seen between the spectra of Y, CH$_3$CH$_2$COCH$_3$, and of 2-methylbut-1-ene. Give reasons for your predictions.
Your answer should refer only to the region of each spectrum above 1500cm$^{-1}$.
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(f) Propanoic acid, CH$_3$CH$_2$CO$_2$H, is reduced by LiAlH$_4$.
(i) Write an equation to show this reaction. Use [H] to represent an atom of hydrogen from the reducing agent.
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(ii) Name the organic product formed in this reaction.
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(g) Organic compound W is an ester which is a structural isomer of propanoic acid.
(i) State the molecular formula of W.
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(ii) Draw a possible structure of W.
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