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

(a) Successive ionisation energies for the elements magnesium to barium are given in the table.

[Table_1]

\begin{table}[h!]
\centering
\begin{tabular}{|c|c|c|c|}
\hline
\text{element} & \text{1st ionisation} & \text{2nd ionisation} & \text{3rd ionisation} \\
& \text{energy}/\text{kJ mol}^{-1} & \text{energy}/\text{kJ mol}^{-1} & \text{energy}/\text{kJ mol}^{-1} \\
\hline
\text{Mg} & 736 & 1450 & 7740 \\
\hline
\text{Ca} & 590 & 1150 & 4940 \\
\hline
\text{Sr} & 548 & 1060 & 4120 \\
\hline
\text{Ba} & 502 & 966 & 3390 \\
\hline
\end{tabular}
\end{table}

(i) Explain why the first ionisation energies decrease down the group.
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[3]

(ii) Explain why, for each element, there is a large increase between the 2nd and 3rd ionisation energies.
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[2]

(b) A sample of strontium, atomic number 38, gave the mass spectrum shown. The percentage abundances are given above each peak.



(i) Complete the full electronic configuration of strontium.
1s^2 2s^2 2p^6 .................................................. [1]

(ii) Explain why there are four different peaks in the mass spectrum of strontium.
...............................................................................................................................................................
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[1]

(iii) Calculate the atomic mass, A_r, of this sample of strontium. Give your answer to three significant figures.
A_r = ........................ [2]

(c) A compound of barium, A, is used in fireworks as an oxidising agent and to produce a green colour.
(i) Explain, in terms of electron transfer, what is meant by the term \textit{oxidising agent}.
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[1]

(ii) A has the following percentage composition by mass: Ba, 45.1; Cl, 23.4; O, 31.5.
Calculate the empirical formula of A.
empirical formula of A ........................................... [3]

(d) Some reactions involving magnesium and its compounds are shown in the reaction scheme below.



(i) Give the \textit{formulae} of the compounds X, Y and Z.
X ..................................................
Y ..................................................
Z ..................................................
[3]

(ii) Name the reagent needed to convert Y(s) into Z(aq) in reaction 1 and write an equation for the reaction.
reagent ..................................................
equation ..................................................
[2]

(iii) How would you convert a sample of Z(s) into Y(s) in reaction 2?
...............................................................................................................................................................
[1]

(iv) Give equations for the conversions of Mg into X, and Z(s) into Y.
Mg to X ..................................................
Z to Y ..................................................
[2]

(a) One way in which the sulfur dioxide for this reaction is produced is by heating the sulfide ore iron pyrites, FeS_2, in air. Iron(III) oxide is also produced. Write an equation for this reaction.

(b) The sulfur trioxide produced in the Contact process is reacted with 98% sulfuric acid. The resulting compound is then reacted with water to produce sulfuric acid.
(i) Explain why the sulfur trioxide is not first mixed directly with water. [1]
(ii) Write equations for the two steps involved in the conversion of sulfur trioxide into sulfuric acid. [2]

(c) (i) Sulfur dioxide and sulfur trioxide both contain only S=O double bonds.
Draw labelled diagrams to show the shapes of these two molecules.
SO_2
SO_3 [2]
(ii) For your diagrams in (i), name the shapes and suggest the bond angles.
SO_2 shape ................................. SO_3 shape .................................
SO_2 bond angle ........................ SO_3 bond angle .................... [2]

(d) The conversion of sulfur dioxide into sulfur trioxide is carried out at a temperature of 400°C.
(i) With reference to Le Chatelier's Principle and reaction kinetics, state and explain one advantage and one disadvantage of using a higher temperature. [4]
(ii) State the expression for the equilibrium constant, $K_p$, for the formation of sulfur trioxide from sulfur dioxide.
$K_p = $……. [1]
(iii) 2.00 moles of sulfur dioxide and 2.00 moles of oxygen were put in a flask and left to reach equilibrium. At equilibrium, the pressure in the flask was $2.00 \times 10^5$ Pa and the mixture contained 1.80 moles of sulfur trioxide.
Calculate $K_p$. Include the units.
$K_p = $………
units = ............. [5]

P, Q and R are structural isomers with the molecular formula $C_4H_8$.
All three compounds readily decolourise bromine in the dark.
P and Q do not exhibit stereoisomerism but R exists as a pair of geometrical (cis-trans) isomers.
All three compounds react with hot concentrated, acidified potassium manganate(VII) to produce a variety of products as shown in the table.
[Table_1]
$$\begin{array}{|c|c|}\hline \text{compound} & \text{products} \\ \hline P & \text{CO}_2 \text{ and S } (\text{C}_3\text{H}_6\text{O})\\ Q & \text{CO}_2 \text{ and } \text{CH}_3\text{CH}_2\text{CO}_2\text{H} \\ R & \text{CH}_3\text{CO}_2\text{H only} \\ \hline \end{array}$$
S reacts with 2,4-dinitrophenylhydrazine reagent, 2,4-DNPH, to form an orange crystalline product but does not react with Fehling’s reagent.

(a) Give the structural formulae of P, Q, R and S.
P .................................................... Q ....................................................
R .................................................... S .................................................... [4]

(b) (i) Explain what is meant by the term stereoisomerism.
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.............................................................................................................. [2]

(ii) Draw the displayed formulae of the geometrical isomers of R and name them both.
name ........................................ name ........................................ [2]

(c) State a reagent that could be used for the reduction of S and name the organic product of this reduction.
reagent ......................................... product ......................................... [2]

A series of reactions based on propanoic acid is shown.

(a) Write an equation for reaction 1, using [H] to represent the reducing agent.
.................................................................................................................................................. [2]
(b) (i) What type of reaction is reaction 2?
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(ii) Suggest a suitable reagent and conditions for reaction 2.
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(c) Write an equation for the reaction of propanoic acid with calcium carbonate, CaCO₃.
.................................................................................................................................................. [2]
(d) (i) Suggest a suitable reagent and conditions for reaction 3.
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.................................................................................................................................................. [2]
(ii) Identify the other product of reaction 3.
.................................................................................................................................................. [1]