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

The graph shows the first ionisation energies of some of the elements in Group 2.


(a) Write an equation for the first ionisation energy of Mg.
Include state symbols.
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(b) Explain the observed trend in first ionisation energies down Group 2.
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(c) The second ionisation energy of Be is 1757 kJ mol⁻¹.
Explain why the second ionisation energy of Be is higher than the first ionisation energy of Be.
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(a) Phosphorus reacts with an excess of oxygen to form phosphorus(V) oxide.
(i) Write an equation to show the reaction of phosphorus with excess oxygen.
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(ii) Describe the reaction of phosphorus(V) oxide with water.
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(iii) State the structure and bonding of solid phosphorus(V) oxide.
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The two most common oxides of sulfur are $SO_2$ and $SO_3$.
When $SO_2$ dissolves in water, a small proportion of it reacts with water to form a weak
Brønsted-Lowry acid.
(i) Explain the meaning of the term weak Brønsted-Lowry acid.
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(ii) Write the equation for the reaction of $SO_2$ with water.
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(iii) $SO_2$ reacts with $NO_2$ in the atmosphere to form $SO_3$ and $NO$.

$NO$ is then oxidised in air to form $NO_2$.

$$SO_2 + NO_2 \rightarrow SO_3 + NO$$

$$2NO + O_2 \rightarrow 2NO_2$$

State the role of $NO_2$ in this two-stage process.
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(c) Emissions of $SO_2$ from coal-fired power stations can be reduced by mixing the coal with powdered limestone.

Limestone is heated to form $CaO$ in reaction 1. This then reacts with $SO_2$ and $O_2$ to form $CaSO_4$ in reaction 2.

reaction 1: $CaCO_3(s) \rightarrow CaO(s) + CO_2(s)$

reaction 2: $CaO(s) + SO_2(g) + \frac{1}{2}O_2(g) \rightarrow CaSO_4(s)$
(i) State the type of reaction occurring in reaction 1.
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(ii) Use the data to calculate the enthalpy change of reaction 2.

[Table_1]

enthalpy change of reaction 2 = ........................... kJ mol$^{-1}$ [2]

(d) Chlorine forms several oxides, including $Cl_2O$, $ClO_2$ and $Cl_2O_6$.

(i) Draw a ‘dot-and-cross’ diagram of $Cl_2O$. Show outer-shell electrons only.


[1]
(ii) $ClO_2$ can be prepared by reacting $NaClO_2$ with $Cl_2$.

Write the oxidation state of chlorine in each species in the boxes provided.

$$2NaClO_2 + Cl_2 \rightarrow 2ClO_2 + 2NaCl$$

oxidation state of chlorine: +3
[1]
(iii) $Cl_2O_6(g)$ is produced by the reaction of $ClO_2(g)$ with $O_3(g)$.

$$2ClO_2(g) + 2O_3(g) \rightleftarrows Cl_2O_6(g) + 2O_2(g) \quad \Delta H = -216 \text{kJ mol}^{-1}$$

The reaction takes place at 500K and 100kPa.

State and explain the effect on the yield of $Cl_2O_6(g)$ when the experiment is carried out:
● at 1000K and 100kPa
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● at 500K and 500kPa.
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Element E is a Period 5 element.
E reacts with oxygen to form an insoluble white oxide that has a melting point of 1910°C. The oxide of E conducts electricity only when liquid.

E also reacts readily with $Cl_2(g)$ to form a white solid that reacts exothermically with water. The resulting solution reacts with aqueous silver nitrate to form a white precipitate that dissolves in dilute ammonia.

(i) Suggest the type of bonding shown by the oxide of E. Explain your answer.
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(ii) Suggest the type of bonding shown by the chloride of E. Explain your answer.
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[Total: 21]

(a) (i) At 200°C, aluminium chloride exists as $Al_2Cl_6(g)$.
Draw the structure of $Al_2Cl_6(g)$, showing fully any coordinate (dative covalent) bonds in the molecule.
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(ii) At 1000°C, aluminium chloride exists as $AlCl_3(g)$.
State the bond angle in $AlCl_3(g)$.
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(iii) Lithium hydride contains the ions $Li^+$ and $H^-$.
State the electronic configuration of these two ions.
$Li^+$ ................................................ $H^-$ ......................................................
[1]
(iv) $LiAlH_4$ decomposes slowly to form $LiAl(s)$ and $H_2(g)$.
$$LiAlH_4(s) \rightarrow LiAl(s) + 2H_2(g)$$
$LiAl(s)$ shows metallic bonding.
Describe metallic bonding.
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[1]

(b) $LiAlH_4$ cannot be used in aqueous solution because it reacts with water to produce $LiOH(aq)$, $H_2(g)$ and a white precipitate which is soluble in excess sodium hydroxide.
Identify the white precipitate.
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[1]

(c) Two students try to prepare 2-hydroxybutanoic acid in the laboratory.



Both students oxidise butane-1,2-diol to form P in reaction 1.
One student then reduces P using $LiAlH_4$. Q is formed.
The other student reduces P using $NaBH_4$. R is formed.



(i) State the reagents and conditions required for reaction 1.
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(ii) Only one of the students successfully prepares 2-hydroxybutanoic acid.
Identify which of Q or R is 2-hydroxybutanoic acid and explain the difference between reactions 2 and 3.
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A third student prepares 2-hydroxybutanoic acid using propanal as the starting material. In step 1 the student reacts propanal with a mixture of NaCN and HCN.



(iii) Draw the mechanism for the reaction of propanal with the mixture of NaCN and HCN to form S.
• Identify the ion that reacts with propanal.
• Draw the structure of the intermediate of the reaction.
• Include all charges, partial charges, lone pairs and curly arrows.



[4]
(iv) Complete the equation for the reaction in step 2, when S is heated under reflux with $HCl(aq)$.
$C_2H_5CH(OH)CN +$ .................................... $\rightarrow C_2H_5CH(OH)COOH +$ ..............................
[1]
(v) The infrared spectrum of an organic compound is shown. The organic compound is either S or 2-hydroxybutanoic acid.



Deduce the identity of the compound. Give two reasons for your answer.
In your answer, identify any relevant absorptions above $1500\text{ cm}^{-1}$ in the spectrum and the bonds that correspond to these absorptions.
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[Total: 17]

(a) (i) State and explain the trend in volatility of the halogens, from chlorine to iodine.
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(ii) Explain why HI is the \textit{least} thermally stable of HCl, HBr and HI.
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(iii) The table shows the electronegativity values for hydrogen, fluorine and iodine.

| element | electronegativity value |
| ------- | ---------------------- |
| H | 2.1 |
| F | 4.0 |
| I | 2.5 |

Explain, in terms of intermolecular forces, why HI has a lower boiling point than HF.
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(iv) Iodine reacts with hot concentrated aqueous sodium hydroxide in the same way as chlorine.
Write an equation for the reaction of iodine and hot aqueous sodium hydroxide.
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(b) Iodoalkanes contain carbon-iodine bonds.
The simplest iodoalkane is CH$_3$I.

(i) CH$_3$I can be made from methanol, CH$_3$OH.
Identify a reagent that can convert CH$_3$OH to CH$_3$I.
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(ii) 1,2-diiodoethane, CH$_2$ICH$_2$I, can be made by bubbling ethene into liquid iodine.
Fully name the type of mechanism shown in this reaction.
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(c) J reacts with NaOH, forming different products dependent on the conditions used.


(i) Name J.
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(ii) J reacts with NaOH(aq) to form K.


Fully name the mechanism of the reaction of J with NaOH(aq) to form K.
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(iii) J reacts with NaOH dissolved in ethanol to form a mixture of two alkenes, L and M. Alkene L is shown.


In the box provided, draw the structure of M. [1]

(iv) Explain why L does \textit{not} show geometrical (cis-trans) isomerism.
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(v) L reacts with hot concentrated acidified KMnO$_4$(aq) to form propanone and one other organic product.
Identify the other organic product.
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(vi) Propanone reacts with excess alkaline aqueous iodine.
Complete and balance the equation for this reaction.
CH$_3$COCH$_3$ + ....I$_2$ + ....OH^- \rightarrow ....CH$_3$COO^- + ......H$_2$O + ......I^- + ................. [2]

(vii) State one observation that can be made in the reaction in (c)(vi).
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