AS & A Level Chemistry - 9701 Paper 2 2017 Winter Zone 2

The elements sodium to sulfur react with chlorine. The melting points of some of the chlorides formed are shown.

[Table_1]

(a) Predict the shapes of $\text{AlCl}_3$ and $\text{PCl}_3$.

Draw diagrams to show the shapes, name the shapes and state the bond angles.



shape ..................................................
angle ..................................................
shape ..................................................
angle ..................................................

[4]

(b) (i) Explain, in terms of structure and bonding, why the melting point of $\text{SiCl}_4$ is much lower than that of $\text{NaCl}$.
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[3]

(ii) Explain why the melting point of $\text{SiCl}_4$ is higher than that of $\text{PCl}_3$.
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[2]

(iii) Draw the 'dot-and-cross' diagram of a molecule of $\text{SiCl}_4$. Show outer electrons only.
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[1]

At 450 K phosphorus(V) chloride, $PCl_5(g)$, decomposes to form phosphorus(III) chloride, $PCl_3(g)$, and chlorine, $Cl_2(g)$. A dynamic equilibrium is established as shown.
$$PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g) \quad \Delta H = +124 \text{kJ} \text{mol}^{-1}$$

(a) The enthalpy change of formation of $PCl_3(g)$ under these conditions is given.

$$\Delta H_f \hspace{3px} PCl_3(g) = -320 \text{kJ mol}^{-1}$$

Calculate the enthalpy change of formation of $PCl_5(g)$ under these conditions.
Include a sign with your answer.

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

(b) (i) State and explain the effect of increasing temperature on the rate of decomposition of $PCl_5(g)$.
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(ii) State and explain the effect of increasing temperature on the percentage of $PCl_5(g)$ that decomposes.
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(c) Explain the meaning of the term dynamic equilibrium and the conditions necessary for it to become established.
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(d) When $2.00 \text{ mol}$ of $PCl_5(g)$ are decomposed at 450 K and $1.00 \times 10^5 \text{ Pa}$ the resulting equilibrium mixture contains $0.800 \text{ mol}$ of $Cl_2(g)$.

(i) Calculate the partial pressure of phosphorus(V) chloride, $pPCl_5$, in this equilibrium mixture.

$pPCl_5 = ............................. \text{Pa}$ [2]

(ii) Write the expression for the equilibrium constant, $K_p$, for the decomposition of $PCl_5(g)$.

$K_p = $.................................................................................................. [1]

(iii) The partial pressures of $PCl_3(g)$ and of $Cl_2(g)$ in this equilibrium mixture are both $2.86 \times 10^4 \text{ Pa}$.

Calculate the value of $K_p$ and state its units.

$K_p = .............................$
units = ............................. [2]

(a) State and explain the trend in ionisation energy down Group 2. .................................................. .................................................. .................................................. ..................................................

(b) (i) State and explain the trend in melting point down Group 17. .................................................. .................................................. .................................................. (ii) The melting point decreases down Group 2. Explain this trend. .................................................. .................................................. ..................................................

(c) (i) State the reagent needed for each of reactions 1 and 2. reaction 1 .................................................. reaction 2 ..................................................

(c) (ii) Name X and write an equation for its formation. name .................................................. equation ..................................................

(c) (iii) The Ba(NO3)2(aq), produced by reaction 1, is heated to dryness. The anhydrous solid is then heated strongly and decomposes. Barium oxide is produced, together with two other products. Identify the two other products of this decomposition reaction and state what would be observed. .................................................. ..................................................

(c) (iv) State what would be observed when excess MgSO4(aq) is added to the Ba(OH)2(aq) produced in reaction 2. Explain your answer. .................................................. .................................................. ..................................................

Some reactions are shown, based on methylpropan-2-ol, $(CH_3)_3COH$.

$(CH_3)_3CBr \xleftrightarrow[reaction\ 2]{reaction\ 1} (CH_3)_3COH \xrightarrow{reaction\ 3} (CH_3)_2C=CH_2 \xrightarrow{reaction\ 4} (CH_3)_3CBr \text{ and } (CH_3)_2CHCH_2Br$

(a) For each of the reactions state the reagent(s), the particular conditions required, if any, and the type of reaction.

For the type of reaction choose from the list.
Each type may be used once, more than once or not at all.
Each reaction may be described by one or more than one type.

hydrolysis dehydration substitution oxidation addition condensation

\begin{center}\begin{tabular}{|c|c|c|} \hline \text{reaction} & \text{reagent(s) and conditions} & \text{type(s) of reaction} \\ \hline 1 & & \\ \hline 2 & & \\ \hline 3 & & \\ \hline 4 & & \\ \hline \end{tabular}\end{center}

[5]

(b) Draw a diagram to show the $S_N1$ mechanism of reaction 2.
Include all necessary charges, dipoles, lone pairs and curly arrows.

[3]

(c) 1-bromobutane is a structural isomer of the product of reaction 1.
(i) Define the term \textit{structural isomer} and name the three different types of structural isomerism.
definition ..........................................................................................................
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types of structural isomerism
1 ..........................................................................................................................
2 ..........................................................................................................................
3 ..........................................................................................................................
[4]

(c) (ii) 1-bromobutane is treated with the same reagents as in reaction 2. Butan-1-ol is formed.
Identify the mechanism of this reaction.
Explain why this reaction proceeds via a different mechanism than that of reaction 2.
mechanism ........................................................................................................
explanation ........................................................................................................
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[3]

(d) The product of reaction 3, methylpropene, does \textbf{not} show stereoisomerism.
(i) Give two reasons why methylpropene does \textbf{not} show stereoisomerism.
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[2]

(d) (ii) Methylpropene can be polymerised to form a poly(alkene).
State the type of polymerisation and draw the repeat unit of the polymer formed from methylpropene.
type of polymerisation .....................................................................................
repeat unit
[3]

(d) (iii) State the difficulty associated with the disposal of poly(alkenes).
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[1]

(e) Name the two products of reaction 4.
name of $(CH_3)_3CBr$ ...............................................................................
name of $(CH_3)_2CHCH_2Br$ ...............................................................................
[2]