6244 june 2009 qp

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SurnameCentre No. Candidate No.Paper Reference(s)

Initial(s)

Paper Reference Signature

6 2 4 46244/01

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Examiners use only

Edexcel GCEChemistryAdvanced Unit Test 4Thursday 11 June 2009 Afternoon Time: 1 hour 30 minutes

Team Leaders use only

Question Leave Number Blank

1 2 3 4 5

Materials required for examination Nil Candidates may use a calculator.

Items included with question papers Nil

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Instructions to CandidatesIn the boxes above, write your centre number, candidate number, your surname, initial(s) and signature. Check that you have the correct question paper. The paper reference is shown above. Answer ALL the questions. Write your answers in the spaces provided in this question paper. Do not use pencil. Use blue or black ink. Show all the steps in any calculations and state the units.

Information for CandidatesThe marks for individual questions and parts of questions are shown in round brackets: e.g. (2). The total mark for this paper is 75. There are 20 pages in this question paper. Any blank pages are indicated. A Periodic Table is printed on the back cover of this paper.

Advice to CandidatesYou are reminded of the importance of clear English and careful presentation in your answers.

TotalThis publication may be reproduced only in accordance with Edexcel Limited copyright policy. 2009 Edexcel Limited. Printers Log. No.

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N33911AW850/R6244/57570 7/7/7/3/

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Answer ALL the questions. Write your answers in the spaces provided. 1. (a) Sodium oxide, Na2O, and phosphorus(V) oxide, P4O10, are both hydrolysed by water. (i) When water is added to sodium oxide, a solution of sodium hydroxide is formed. Write the equation for the reaction of sodium oxide with excess water. State symbols are not required. ................................................................................................................................ (1) (ii) Write the equation, including state symbols, for the reaction of phosphorus(V) oxide with water. ............................................................................................................................... (2) (iii) State the type of bonding in these two compounds and explain in terms of the bonds present the action of water on each. Bonding in sodium oxide ...................................................................................... Bonding in phosphorus(V) oxide .......................................................................... Explanation ............................................................................................................ ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... (4)

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(b) Potassium forms a superoxide, KO2, which reacts with water as follows 2KO2(s) + 2H2O(l) 2KOH(aq) + H2O2(aq) + O2(g) Calculate the maximum volume of oxygen produced when 1.2 g of potassium superoxide is added to excess water. [The molar volume of oxygen under the conditions of the experiment = 24 dm3 mol1]

(2) (Total 9 marks)

Q1

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2.

(a) Define the terms (i) lattice energy ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... (2) (ii) enthalpy of atomisation of an element ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... (2) (b) Calculation of the lattice energy of an ionic compound from a purely ionic model often gives a value that is different from the experimental value obtained from a Born-Haber cycle. (i) What causes the values to be different for some compounds? ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... (1) (ii) Stating your reasons, suggest which of the substances with formulae MgF2 or MgI2 would show the greater difference between the calculated and experimental values of the lattice energy. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... (2) (Total 7 marks)

Q2

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3.

(a) What is meant by a Brnsted-Lowry acid? ....................................................................................................................................... (1) (b) Propanoic acid, CH3CH2COOH, dissociates in water and has a Ka value of 1.30 105 mol dm3 at 25 C. CH3CH2COOH + H2O (i) Write the expression for Ka. CH3CH2COO- + H3O+

(1) (ii) Calculate the H3O+ ion concentration in propanoic acid of concentration 0.100 mol dm3 at 25 C. You may assume that [H3O+] = [CH3CH2COO].

(1) (iii) What other assumption has to be made when calculating the H3O+ ion concentration in (ii)? Explain whether it is justified. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... (2)

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(c) A solution of sodium propanoate in water is alkaline. (i) Write an ionic equation to show why a solution of sodium propanoate is alkaline. ............................................................................................................................... (1) (ii) The pH of a solution of sodium propanoate of concentration 0.100 mol dm3 is 8.94 at 25 C. Calculate the concentration of the hydroxide ions in this solution. [Kw = 1.00 1014 mol2 dm6 at 25 C]

(2) (d) An aqueous mixture of propanoic acid and sodium propanoate is a buffer. (i) Explain, using suitable equations, how this mixture acts as a buffer. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... (4)6

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(ii) Calculate the pH o