AS & A Level Chemistry - 9701 Paper 2 2013 Summer Zone 3

Carbon disulfide, CS$_2$, is a volatile, flammable liquid which is produced in small quantities in volcanoes.

(a) The sequence of atoms in the CS$_2$ molecule is sulfur to carbon to sulfur.

(i) Draw a 'dot-and-cross' diagram of the carbon disulfide molecule. Show outer electrons only.

(ii) Suggest the shape of the molecule and state the bond angle.

shape ........................................................
bond angle ........................................................ [3]

(b) Carbon disulfide is readily combusted to give CO$_2$ and SO$_2$.

(i) Construct a balanced equation for the complete combustion of CS$_2$.

........................................................................................ [3]

(ii) Define the term standard enthalpy change of combustion, $\Delta H_c^{\circ}$.
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(c) Calculate the standard enthalpy change of formation of CS$_2$ from the following data. Include a sign in your answer.

standard enthalpy change of combustion of CS$_2$ = -1110 kJ mol$^{-1}$
standard enthalpy change of formation of CO$_2$ = -395 kJ mol$^{-1}$
standard enthalpy change of formation of SO$_2$ = -298 kJ mol$^{-1}$ [3]

(d) Carbon disulfide reacts with nitrogen monoxide, NO, in a 1:2 molar ratio. A yellow solid and two colourless gases are produced.

(i) Construct a balanced equation for the reaction.
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(ii) What is the change in the oxidation number of sulfur in this reaction?
from ........................................................ to ........................... [3]

Methanol, $\text{CH}_3\text{OH}$, can be produced industrially by reacting carbon monoxide, CO, with hydrogen, $\text{H}_2$:

$$\text{CO(g)} + 2\text{H}_2\text{(g)} \rightleftharpoons \text{CH}_3\text{OH(g)} \quad \Delta H = -91 \text{kJ mol}^{-1}$$

The process is carried out at $4 \times 10^3$ kPa (40 atmospheres) and 1150 K.

(a) (i) State Le Chatelier's Principle.

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(ii) From your understanding of Le Chatelier’s Principle, state the conditions of temperature and pressure that could be used in order to produce an increased yield of methanol in this process.
In each case, explain why the yield would increase.

temperature ...............................................................................................................................
explanation ...............................................................................................................................
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pressure ..................................................................................................................................
explanation ...............................................................................................................................
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(b) The carbon monoxide for use in the production of methanol may be formed by reacting carbon dioxide with hydrogen.

$$\text{CO}_2\text{(g)} + \text{H}_2\text{(g)} \rightleftharpoons \text{CO(g)} + \text{H}_2\text{O(g)} \quad K_c = 1.44 \text{ at } 1200 \text{ K}$$

A mixture containing 0.70 mol of $\text{CO}_2$, 0.70 mol of $\text{H}_2$, 0.30 mol of CO and 0.30 mol of $\text{H}_2\text{O}$ was placed in a 1 dm³ flask and allowed to come to equilibrium at 1200 K.

Calculate the amount, in moles, of each substance present in the equilibrium mixture at 1200 K.

$$\begin{align*} & \text{CO}_2 & + & \text{H}_2 & \rightleftharpoons & \text{CO} & + & \text{H}_2\text{O} \\ \text{initial moles} & 0.70 & & 0.70 & & 0.30 & & 0.30 \\ \end{align*}$$ [4]

This question refers to the elements in the section of the Periodic Table shown below.

(a) From this list of elements, identify in each case one element that has the property described. Give the symbol of the element.
(i) An element that has molecules which consist of single atoms.
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(ii) An element that has a molecule which contains exactly four atoms.
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(iii) The element that is a liquid at room temperature and pressure.
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(iv) The element in Period 3 (Na to Ar) that has the largest atomic radius.
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(v) The element in Period 3 (Na to Ar) that has the highest melting point.
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(vi) The element in Period 3 (Na to Ar) that forms the largest anion.
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(vii) An element that reacts with water to give a solution that can behave as an oxidising agent.
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(b) The formulae and melting points of some of the oxides of the elements in Period 3, Na to Cl, are given in the table.
[Table_1]
(i) Give the formulae of two of these oxides that have simple molecular structures.
..................... and .....................
(ii) Give the formula of one of these oxides that will give no reaction with water when placed in it for a long time.
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(iii) Give the formula of the product formed when MgO is reacted with SO$_2$.
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(c) The melting points of the elements Si to Cl are given in the table.
[Table_2]
(i) Explain why the melting point of Si is very much greater than those of the other three elements.
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(ii) Suggest why the melting points of the other three elements are in the order S > P > Cl.
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Compound $Q$, heptan-2-one, is found in some blue cheeses.
$\text{CH}_3(\text{CH}_2)_4\text{COCH}_3$
compound $Q$
(a) Compound $Q$ may be reduced to $R$.
Compound $R$ may be dehydrated to give two different products, $S$ and $T$.
(i) In the boxes below, draw the structural formulae of $R$, $S$, and $T$.
$\text{CH}_3(\text{CH}_2)_4\text{COCH}_3$
\[ \text{reduce} \]
\[ \begin{array}{ccc} \qquad & \text{R} \qquad & \qquad \\ \downarrow \text{dehydrate} & \downarrow & \downarrow \\ \text{S} & & \text{T} \end{array} \]
(ii) State the reagents that would be used for each of these reactions in a school or college laboratory.
reduction .........................................................
dehydration .........................................................
[5]

(b) In the boxes below, write the structural formula of the organic compound formed when $Q$ is reacted separately with each reagent under suitable conditions.
If you think no reaction occurs, write 'NO REACTION' in the box.
\[ \begin{array}{|c|c|} \hline \text{Tollens' reagent} & \\ \hline \text{HCN} & \\ \hline \text{K}_2\text{Cr}_2\text{O}_7/\text{H}^+ & \\ \hline \end{array} \]
[3]

(c) The first stage of cheese making is to produce 2-hydroxypropanoic acid (lactic acid) from milk.
$\text{CH}_3\text{CH(OH)CO}_2\text{H}$ lactic acid
Other than the use of a pH indicator, what reagent could you use to confirm the presence of some lactic acid in a sample of heptan-2-one?
State what observation you would make.
reagent .........................................................
observation .........................................................
[2]

(a) Allyl alcohol behaves as a primary alcohol and as an alkene.
Give the structural formula of the organic compound formed when allyl alcohol is reacted separately with each of the following reagents.
(i) acidified potassium dichromate(VI), heating under reflux
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(ii) bromine in an inert organic solvent
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(iii) cold, dilute, acidified potassium manganate(VII)
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(iv) hot, concentrated, acidified potassium manganate(VII)
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(b) Allyl alcohol undergoes the following reactions.
(i) When reacted with concentrated HCl at 100°C, CH$_2$=CHCH$_2$Cl is formed.
State as fully as you can what type of reaction this is.
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(ii) When reacted with MnO$_2$ at room temperature, CH$_2$=CHCHO is formed.
What type of reaction is this?
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(c) Allyl alcohol can be converted into propanal in two steps.
$$\text{CH}_2=\text{CHCH}_2\text{OH} \xrightarrow{\text{step I}} \text{CH}_3\text{CH}_2\text{CH}_2\text{OH} \xrightarrow{\text{step II}} \text{CH}_3\text{CH}_2\text{CHO}$$
(i) What reagents and conditions would be used for each step?
step I
reagent(s) ......................................................................................................................
condition(s) ....................................................................................................................
step II
reagent(s) ......................................................................................................................
condition(s) ....................................................................................................................
(ii) Allyl alcohol and propanal are isomers.
What form of isomerism do they display?
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(d) Allyl alcohol may also be converted into propanal by using a ruthenium(IV) catalyst in water.
$$\text{CH}_2=\text{CHCH}_2\text{OH} \xrightarrow{\text{ruthenium(IV) catalyst}} \text{CH}_3\text{CH}_2\text{CHO}$$
Suggest what is unusual about this single step reaction.
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