Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2012 Winter Zone 2

This question is concerned with the elements in Period 5, Rb to Xe.

(a) The electron distributions of some of these elements are given in the following list.

element A: 2 + 8 + 18 + 8 + 2
element B: 2 + 8 + 18 + 18 + 8
element C: 2 + 8 + 18 + 18 + 5
element D: 2 + 8 + 18 + 18 + 6
element E: 2 + 8 + 18 + 18 + 4
element F: 2 + 8 + 18 + 18 + 7

(i) Identify element C. ................................................. [1]
(ii) Which element in the list does not form any compounds?
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(iii) Which element in the list forms a chloride of the type $XCl_2$?
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(iv) Which two elements would react together to form a compound of the type $XY_4$?
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(v) Which element in the list would react with cold water to form an alkaline solution and hydrogen?
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(b) Predict two differences in physical properties and two differences in chemical properties between rubidium and the transition metal niobium.

physical ...............................................................
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chemical .............................................................
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The diagram shows a heating curve for a sample of compound X.

(a) Is X a solid, a liquid or a gas at room temperature, 20°C?
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(b) Write an equation for the equilibrium which exists in region BC.
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(c) Name the change of state which occurs in region DE.
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(d) Explain how the curve shows that a pure sample of compound X was used.
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Many organic compounds which contain a halogen have chloro, bromo or iodo in their name.
(a) The following diagram shows the structure of 1-chloropropane.

(i) Draw the structure of an isomer of this compound. [1]
(ii) Describe how 1-chloropropane could be made from propane.
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(iii) Suggest an explanation why the method you have described in (ii) does not produce a pure sample of 1-chloropropane.
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(b) Organic halides react with water to form an alcohol and a halide ion.
$$ \text{CH}_3-\text{CH}_2-\text{I} + \text{H}_2\text{O} \rightarrow \text{CH}_3-\text{CH}_2-\text{OH} + \text{I}^- $$
(i) Describe how you could show that the reaction mixture contained an iodide ion.
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(ii) Name the alcohol formed when 1-chloropropane reacts with water.
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(c) The speed (rate) of reaction between an organic halide and water can be measured by the following method.
A mixture of 10 cm³ of aqueous silver nitrate and 10 cm³ of ethanol is warmed to 60°C. Drops of the organic halide are added and the time taken for a precipitate to form is measured.
Silver ions react with the halide ions to form a precipitate of the silver halide.
$$ \text{Ag}^+(\text{aq}) + \text{X}^-(\text{aq}) \rightarrow \text{AgX}(\text{s}) $$
Typical results for four experiments, A, B, C and D, are given in the table.
[Table_1]
(i) Explain why it takes longer to produce a precipitate in experiment A than in B.
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(ii) How does the order of reactivity of the organic halides compare with the order of reactivity of the halogens?
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(iii) Explain why the time taken to produce a precipitate would increase if the experiments were repeated at 50°C.
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Iron is extracted from its ore, hematite, in the blast furnace.

(a) The temperature inside the blast furnace can rise to 2000°C. Write an equation for the exothermic reaction which causes this high temperature.
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(b) Carbon monoxide is formed in the blast furnace. This reduces the ore hematite, $Fe_2O_3$, to iron.

(i) Explain how carbon monoxide is formed in the blast furnace.
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(ii) Write an equation for the reduction of hematite by carbon monoxide.
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(c) Explain why it is necessary to add limestone, calcium carbonate, to the blast furnace. Include an equation in your explanation.
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(d) Most of the iron from the blast furnace is converted into mild steel. A method of preventing the steel from rusting is coating it with zinc.

(i) What is the name of this method of rust prevention?
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(ii) Explain, using the idea of electron transfer, why zinc-coated steel does not rust even when the coating is scratched and the steel is in contact with oxygen and water.
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The food additive E220 is sulfur dioxide. It is a preservative for a variety of foods and drinks.
(a) State two other uses of sulfur dioxide.
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(b) How is sulfur dioxide manufactured?
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(c) Sulfur dioxide is a reductant (reducing agent). Describe what you would see when aqueous sulfur dioxide is added to acidified potassium manganate(VII).
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(d) Sulfur dioxide can also be made by the reaction between a sulfite and an acid.
$$\text{Na}_2\text{SO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{SO}_2 + \text{H}_2\text{O}$$
Excess hydrochloric acid was added to 3.15g of sodium sulfite. Calculate the maximum volume, measured at r.t.p., of sulfur dioxide which could be formed. The mass of one mole of $\text{Na}_2\text{SO}_3$ is 126g.
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During electrolysis, ions move in the electrolyte and electrons move in the external circuit. Reactions occur at the electrodes.
(a) The diagram shows the electrolysis of molten lithium iodide.
(i) Draw an arrow on the diagram to show the direction of the electron flow in the external circuit. [1]
(ii) Electrons are supplied to the external circuit. How and where is this done?
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(iii) Explain why solid lithium iodide does not conduct electricity but when molten it is a good conductor.
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(b) The results of experiments on electrolysis are shown in the following table. Complete the table. The first line has been done as an example.
[Table_1]
electrolyte | electrodes | product at cathode | product at anode | change to electrolyte
molten lithium iodide | carbon | lithium | iodine | used up
aqueous copper(II) sulfate | platinum | ..... | oxygen
concentrated aqueous potassium chloride | carbon | ..... | chlorine
[4]
(c) The diagram below shows the electrolysis of dilute sulfuric acid. Hydrogen is formed at the negative electrode (cathode) and oxygen at the positive electrode (anode) and the concentration of sulfuric acid increases.
The ions present in the dilute acid are $\text{H}^+(aq)$, $\text{OH}^-(aq)$, and $\text{SO}_4^{2-}(aq)$.
(i) Write an equation for the reaction at the negative electrode (cathode).
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(ii) Complete the equation for the reaction at the positive electrode (anode).
$4\text{OH}^-(aq) \rightarrow \text{O}_2(g) + .....\text{H}_2\text{O}(l) + .......$ [1]
(iii) Suggest an explanation of why the concentration of the sulfuric acid increases.
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(d) In the apparatus used in (c), the power supply is removed and immediately replaced by a voltmeter.
A reading on the voltmeter shows that electrical energy is being produced. Suggest an explanation for how this energy is produced.
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(a) (i) Give the general formula of the alcohols.
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(ii) The mass of one mole of an alcohol is 116 g. What is its formula? Show your reasoning.
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(iii) Draw a diagram showing the arrangement of the outer (valency) electrons in one molecule of methanol.
Use x to represent an electron from a carbon atom.
Use o to represent an electron from a hydrogen atom.
Use ● to represent an electron from an oxygen atom. [3]

(b) Methanol is manufactured using the following method.
$$\text{CH}_4(g) + \text{H}_2\text{O}(g) \rightarrow \text{CO}(g) + 3\text{H}_2(g) \quad \text{reaction 1}$$
$$\text{CO}(g) + 2\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g) \quad \text{reaction 2}$$
The conditions for reaction 2 are:
pressure 100 atmospheres
catalyst a mixture of copper, zinc oxide and aluminium oxide
temperature 250°C
The forward reaction is exothermic.

(i) Why is high pressure used in reaction 2?
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(ii) Explain why using a catalyst at 250°C is preferred to using a higher temperature of 350°C and no catalyst.
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(c) Methanol is oxidised by atmospheric oxygen. This reaction is catalysed by platinum.

(i) The products of this reaction include a carboxylic acid. Give its name and structural formula.
name .......................................................
structural formula showing all bonds [2]

(ii) Deduce the name of the ester formed by the reaction of methanol with the carboxylic acid named in (i).
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