AS & A Level Chemistry - 9701 Paper 2 2015 Summer Zone 2

(a) Chemists recognise that atoms are made of three types of particle.

Complete the following table with their names and properties.

[Table_1]

[3]

(b) Most elements exist naturally as a mixture of isotopes, each with their own relative isotopic mass. The mass spectrum of an element reveals the abundances of these isotopes, which can be used to calculate the relative atomic mass of the element.

Magnesium has three stable isotopes. Information about two of these isotopes is given.

[Table_2]

(i) Define the term relative isotopic mass.
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[2]

(ii) The relative atomic mass of magnesium is 24.3.

Calculate the percentage abundance and hence the relative isotopic mass of the third isotope of magnesium. Give your answer to three significant figures

percentage abundance = ........................................

isotopic mass = ............................................
[3]

(c) Magnesium can be produced by electrolysis of magnesium chloride in a molten mixture of salts.

(i) Give equations for the anode and cathode reactions during the electrolysis of molten magnesium chloride, MgCl₂.

anode ...........................................................................................................
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cathode ..........................................................................................................
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[2]

The electrolysis is carried out under an atmosphere of hydrogen chloride gas to convert any magnesium oxide impurity into magnesium chloride.

(ii) An investigation of the reaction between magnesium oxide and hydrogen chloride gas showed that an intermediate product was formed with the composition by mass Mg, 31.65%; O, 20.84%; H, 1.31% and Cl, 46.20%.

Calculate the empirical formula of this intermediate compound.

empirical formula ..........................................[2]

(d) The acid/base behaviour of the oxides in the third period varies across the period.

(i) Describe this behaviour and explain it with reference to the structure and bonding of sodium oxide, Na₂O, aluminium oxide, Al₂O₃, and sulfur trioxide, SO₃.
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[2]

(ii) Write equations for reactions of these three oxides with hydrochloric acid and/or sodium hydroxide as appropriate.
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(a) (i) Write an equation for the reaction between galena and oxygen to form sulfur dioxide and lead(II) oxide.

(a) (ii) Identify the oxidation number changes that take place during this reaction.

(b) The second stage of the Contact process involves the production of sulfur trioxide, SO₃, from sulfur dioxide.
$$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g) \quad \Delta H = -197\text{ kJ mol}^{-1}$$
(i) State the temperature usually chosen for this conversion and explain this in terms of reaction rates and Le Chatelier's principle.
temperature....................................................................................................................
explanation.....................................................................................................................
[3]
(ii) State and explain the pressure conditions that would give the best rate and best yield of sulfur trioxide. Explain why these conditions are not actually used.
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[3]

(c) (i) Explain why the sulfur trioxide is not dissolved directly in water to produce sulfuric acid.

(c) (ii) Write equations for the reaction of sulfur trioxide with sulfuric acid and for the subsequent reaction with water.

(d) Explain why sulfur dioxide is used as an additive in some foods and wines.

(e) The sulfur dioxide content of wine is most commonly measured by the Ripper Method which involves titration with iodine in the presence of starch as an indicator.
$$SO_2(aq) + I_2(aq) + 2H_2O(l) \rightarrow 2I^-(aq) + SO_4^{2-}(aq) + 4H^+(aq)$$
A 50.0 cm³ sample of wine required 12.35 cm³ of 0.010 mol dm⁻³ I₂(aq) for complete reaction with the SO₂.
(i) How many moles of SO₂ are present in 50.0 cm³ of wine?
moles of \(SO_2\) in \(50.0\text{ cm}^3 = \text{................................} \) [1]
(ii) How many moles of SO₂ are present in 1 dm³ of wine?
moles of \(SO_2\) in \(1\text{ dm}^3 = \text{................................} \) [1]
(iii) How many milligrams, mg, of SO₂ are present in 1 dm³ of wine? Give your answer to three significant figures. \(1\text{ g} = 1000 \text{ mg}\)
mass of \(SO_2\) in \(1\text{ dm}^3 = \text{................................} \text{ mg} \) [1]

(a) (i) Use bond energies from the Data Booklet to calculate the enthalpy change for this reaction. Include a sign in your answer.

C₆H₆(g) + Cl₂(g) → C₂H₅Cl(g) + HCl(g)

enthalpy change = ................................. kJ mol⁻¹ [3]
(ii) State the conditions needed for this reaction to occur.
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(iii) Use a series of equations to describe the mechanism of this reaction including the names of each stage and an indication of how butane can be produced as a minor by-product.
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(b) Chloroethane can be converted back into ethane by a two-stage process via an intermediate compound, X.

C₂H₅Cl → (reaction 1) X → (reaction 2) C₂H₆
(i) Give the name of X.
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(ii) Suggest the reagent and conditions needed for reaction 1.
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(iii) Suggest the reagent and conditions needed for reaction 2.
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There are seven structural isomers with the molecular formula $C_5H_{10}O$ that are carbonyl compounds. Four of these are aldehydes.

These four aldehydes, A, B, C and D, have the following properties.

• Aldehyde A has a straight chain while B, C and D are branched.
• Aldehyde B is the only one of the four isomers with a chiral centre and it exists as a pair of optical isomers.
• Aldehyde C has two methyl groups in its structure but D has three.