AS & A Level Chemistry - 9701 Paper 2 2012 Winter Zone 1

(a) One salt which is used as a dietary supplement is a hydrated zinc sulfate, $ZnSO_4.xH_2O$, which is a colourless crystalline solid.

Crystals of zinc sulfate may be prepared in a school or college laboratory by reacting dilute sulfuric acid with a suitable compound of zinc.

Give the formulae of two simple compounds of zinc that could each react with dilute sulfuric acid to produce zinc sulfate.
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(b) A simple experiment to determine the value of $x$ in the formula $ZnSO_4.xH_2O$ is to heat it carefully to drive off the water.

$ZnSO_4.xH_2O(s) \rightarrow ZnSO_4(s) + xH_2O(g)$

A student placed a sample of the hydrated zinc sulfate in a weighed boiling tube and reweighed it. He then heated the tube for a short time, cooled it and reweighed it when cool. This process was repeated four times. The final results are shown below.

[Table 1]

Each of the Group VII elements chlorine, bromine and iodine forms a hydride.
(a) (i) Outline how the relative thermal stabilities of these hydrides change from HCl to HI.
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(ii) Explain the variation you have outlined in (i).
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Hydrogen iodide can be made by heating together hydrogen gas and iodine vapour. The reaction is incomplete.
$$\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$$
(b) Write an expression for $K_c$ and state the units.
$$K_c = \text{.................................} \text{units} \text{....................................}$$

(c) For this equilibrium, the numerical value of the equilibrium constant $K_c$ is 140 at 500 K and 59 at 650 K.
Use this information to state and explain the effect of the following changes on the equilibrium position.
(i) increasing the pressure applied to the equilibrium
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(ii) decreasing the temperature of the equilibrium
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(d) A mixture of 0.02 mol of hydrogen and 0.02 mol of iodine was placed in a 1 dm³ flask and allowed to come to equilibrium at 650 K.
Calculate the amount, in moles, of each substance present in the equilibrium mixture at 650 K.
$$\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$$
[Image of table]
initial moles   0.02  0.02  0

(a) (i) Write a balanced equation, with state symbols, for the reaction occurring in the Haber process.
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(ii) Give three essential operating conditions that are used in the Haber process.
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(iii) State one large scale use of ammonia.
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[5]

(b) Ammonia may be prepared in a school or college laboratory by using the apparatus below.



The reaction involves the displacement of ammonia from one of its compounds.
(i) Give the formulae of the two reactants that are heated together to produce ammonia.
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(ii) Construct a balanced equation for the reaction between your two reagents.
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(iii) Common drying agents include calcium oxide, concentrated sulfuric acid and phosphorus(V) oxide.
Which one of these would be used in the drying tower in this experiment? Explain your answer.
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[5]

(c) Ammonia is a weak base which forms salts containing the ammonium ion.
Describe, with the aid of an equation, the formation and structure of the ammonium ion.
You should use displayed formulae in your answer.
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[3]

(a) The table below lists some oxygen-containing organic compounds and some common laboratory reagents.

(i) Complete the table as fully as you can.
If you think no reaction occurs, write 'no reaction' in the box for the structural formula(e).

[Table]

reaction          organic compound      reagent      structural formula(e) of organic product(s)
A              (CH₃)₃COH               Cr₂O₇²⁻/ H⁺
                                                        heat under reflux
B               CH₃CH₂CHO             Fehling’s reagent
                                                        warm
C               HCO₂CH(CH₃)₂        NaOH(aq)
                                                        warm
D               CH₂=CHCHO           NaBH₄
E               (CH₃)₃COH             NaBH₄
F               CH₃CH₂COCH₃     MnO₄⁻/ H⁺
                                                        heat under reflux

[Table]
(ii) During some of the reactions in (i) a colour change occurs.
Complete the table below for any such reactions, stating the letter of the reaction and what the colour change is.

[Table]

reaction          colour at the beginning of the reaction          colour at the end of the reaction


(b) Some oxygen-containing compounds react with 2,4-dinitrophenylhydrazine.

[Image]

(i) Draw the structural formula of the organic compound formed when HOCH₂CH₂CHO reacts with 2,4-dinitrophenylhydrazine reagent.

(ii) Suggest the colour of the organic product.
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Compound X has the molecular formula $C_4H_8O_2$.
(a) (i) Treatment of X with sodium metal produces a colourless flammable gas.
What does this result tell you about the functional groups that could be present in X?
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(ii) There is no reaction when X is treated with sodium hydrogencarbonate, $NaHCO_3$.
What does this result tell you about the functional groups that could be present in X?
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(iii) When X is shaken with aqueous bromine the orange colour disappears.
What does this result tell you about the functional groups that could be present in X?
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(b) The molecule of X has the following features.
• The carbon chain is unbranched and the molecule is not cyclic.
• No oxygen atom is attached to any carbon atom which is involved in $\pi$ bonding.
• No carbon atom has more than one oxygen atom joined to it.
There are five possible isomers of X which fit these data. Four of these isomers exist as two pairs of stereoisomers.
(i) Draw displayed formulae of each of these two pairs.

(ii) These four isomers of X show two types of stereoisomerism.
State which type of isomerism each pair shows.
pair 1 .................................................................
pair 2 .................................................................