*JUN177405301*

IB/M/Jun17/E4 7405/3

Tuesday 27 June 2017 Morning Time allowed: 2 hours

Materials

For this paper you must have:

• the Periodic Table/Data Booklet, provided as an insert (enclosed)

• a ruler with millimetre measurements

• a calculator, which you are expected to use where appropriate.

Instructions

• Use black ink or black ball-point pen.

• Fill in the boxes at the top of the page.

• Answer all questions.

• You must answer the questions in the spaces provided.

Do not write outside the box around each page or on blank pages.

• All working must be shown.

• Do all rough work in this book.

Cross through any work you do not want to be marked.

Information

• The marks for questions are shown in brackets.

• The maximum mark for this paper is 90.

Advice

• You are advised to spend about 70 minutes on Section A and 50 minutes on Section B.

Please write clearly, in block capitals.

Centre number Candidate number

Surname

Forename(s)

Candidate signature

A-level

CHEMISTRY

Paper 3

For Examiner’s Use

Question Mark

1

2

3

4

Section B

TOTAL

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Section A

Answer all questions in the spaces provided

0 1 Anhydrous magnesium chloride, MgCl2, can absorb water to form the hydrated salt

MgCl2.4H2O

 MgCl2(s) + 4H2O(l) → MgCl2.4H2O(s)

0 1 . 1 Suggest one reason why the enthalpy change for this reaction cannot be determined

directly by calorimetry.

[1 mark]

0 1 . 2 Some enthalpies of solution are shown in Table 1.

Table 1

Salt Enthalpy of solution

/ kJ mol−1

MgCl2(s) −155

MgCl2.4H2O(s) −39

Calculate the enthalpy change for the absorption of water by MgCl2(s) to form

MgCl2.4H2O(s).

[2 marks]

 Enthalpy change kJ mol−1

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0 1 . 3 Describe how you would carry out an experiment to determine the enthalpy of solution

of anhydrous magnesium chloride.

You should use about 0.8 g of anhydrous magnesium chloride.

Explain how your results could be used to calculate the enthalpy of solution.

[6 marks]

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0 1 . 4 Anhydrous magnesium chloride can be formed by direct reaction between its

elements.

 Mg(s) + Cl2(g) → MgCl2(s)

The free-energy change, ∆G, for this reaction varies with temperature as shown in

Table 2.

Table 2

T / K ∆G / kJ mol−1

298 −592.5

288 −594.2

273 −596.7

260 −598.8

240 −602.2

 Use these data to plot a graph of free-energy change against temperature on the grid

opposite.

Calculate the gradient of the line on your graph and hence calculate the entropy

change, ΔS, in J K−1 mol−1

, for the formation of anhydrous magnesium chloride from its

elements.

Show your working.

[5 marks]

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