Edexcel Jun 2013 (R) Paper 1 Q25 (with explained solutions) |

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Edexcel Jun 2013 (R) Paper 1 Q25

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25 *(a) Define the term enthalpy change of neutralization. (2)(b) The enthalpy change of the neutralization reaction between hydrochloric acid, HCl(aq), and sodium hydroxide, NaOH(aq), can be determined by the following procedure. Procedure: x 50.0 cm3 of 2.00 mol dm3 hydrochloric acid is transferred to a polystyrene cup and its temperature recorded x x 50.0 cm3 of 2.00 mol dm3 sodium hydroxide solution is placed in another polystyrene cup and its temperature recorded The two solutions are mixed, with stirring, and the maximum temperature is recorded Results: Initial temperature of both the HCl(aq) and NaOH(aq) = 19.0 qC = 32.5 qC Maximum temperature reached after mixing Assumption: The specific heat capacity of all aqueous solutions is 4.18 J g1 qC1 The density of all aqueous solutions is 1.00 g cm3 *P42982A02124* 21 Turn over<br />
(i) Calculate the heat energy released (in joules) on mixing the hydrochloric acid and the sodium hydroxide solutions. Use the expression energy released (J) = mass of solution4.18temperature change (ii) Calculate the number of moles of hydrochloric acid used in the experiment. (iii) Give the ionic equation, including state symbols, for the reaction between hydrochloric acid and sodium hydroxide solution. (iv) Use your answers to (b)(i), (ii) and (iii) to calculate the enthalpy change of neutralization for the above reaction. Include a sign and units in your answer. (2) (1) (1) (3) 22 *P42982A02224*<br />
(v) Explain why the enthalpy change of neutralization for the reaction between dilute nitric acid, HNO3(aq), and potassium hydroxide solution, KOH(aq), is predicted to be the same as the enthalpy change of neutralization for the reaction carried out in part (b). (1)(Total for Question 25 = 10 marks) TOTAL FOR SECTION B = 60 MARKS TOTAL FOR PAPER = 80 MARKS *P42982A02324* 23<br />

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Mark Acceptable Answers Reject Energy required for 1st mark First mark The enthalpy change when one mole of water is produced (1) Second Mark as a result of the reaction between an acid and an alkali / a base (1) OR First Mark The enthalpy change when one mole of H+ / H3O+ / oxonium / hydronium / hydroxonium (ions) (1) Second Mark Reacts with one mole of / excess / just enough OH (1) ALLOW First mark The enthalpy change when one mole of acid is (just) neutralized (1) Second Mark By (excess) alkali / base (1) ALLOW reverse argument i.e. base neutralising acid Question Number *25(a) 6CH0101R 1306<br />
Question Number 25(b)(i) 5643 without working score 2 marks Acceptable Answers IGNORE any signs First mark Recognition that volume of solution / mass of solution is 100 (cm3 / g ) (1) Second mark T = 13.5 oC (energy released) = 100 x 4.18 x 13.5 = 5643 (J) (1) ALLOW 5.643 kJ IGNORE s.f. except 1 s.f. IGNORE mol1 Question Number 25(b)(ii) (Moles HCl = cHCl x VHCl / 1000=) Acceptable Answers 2.00 x 50.0 1000 = 0.1(00) (mol HCl) IGNORE s.f. Question Number 25(b) (iii) Acceptable Answers H+(aq) + OH(aq)/H2O(l) NOTE: ALL State symbols AND ALL species are required for the mark ALLOW equations with the spectator ions crossed out Reject 5643 kJ Reject Reject Mark Mark Mark 6CH0101R 1306<br />
Question Number 25(b) (iv) Mark Acceptable Answers Reject5.643 = 56.43 kJ mol1 0.1(00) First mark: Correct TE for calculations using answers to (b)(i) and (b)(ii) (1) Second mark: Minus sign (1) Third mark: Final answer in units of kJ mol1 or kJ/mol ALLOW correct answer in J mol-1 if units given (1) IGNORE case of k and J Final answer to 1 s.f. kJ/mol1 or just kJ just J IGNORE s.f. EXCEPT 1 s.f. NOTE: Correct answer, with or without working, scores (3) Question Number 25(b)(v) The ionic equation is the same Acceptable Answers OR number of moles of H+ ions and OH is the same OR number of moles of H+ ions and water is the same OR number of moles of OH ions and water is the same ALLOW Both acid and base are strong and produce 1 mol of water Mark Reject Just forms one mole of water(1) Total for Question 25 = 10 marks Total for Section B = 60 Marks Total for Paper = 80 Marks 6CH0101R 1306<br />

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