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Mark Scheme (Results) January 2013 GCE Chemistry (6CH04) Paper 01 General Principles of Chemistry I Rates, Equilibria and Further Organic Chemistry

Edexcel GCE Chemistry Unit 4 - MS

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6CH04 - Mark Scheme

Text of Edexcel GCE Chemistry Unit 4 - MS

Mark Scheme (Results) January 2013GCE Chemistry (6CH04) Paper 01General Principles of Chemistry I Rates, Equilibria and Further Organic Chemistry

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January 2013 Publications Code US034336 All the material in this publication is copyright Pearson Education Ltd 2013

General Marking Guidance All candidates must receive the same treatment. Examiners must mark the first candidate in exactly the same way as they mark the last. Mark schemes should be applied positively. Candidates must be rewarded for what they have shown they can do rather than penalised for omissions. Examiners should mark according to the mark scheme not according to their perception of where the grade boundaries may lie. There is no ceiling on achievement. All marks on the mark scheme should be used appropriately. All the marks on the mark scheme are designed to be awarded. Examiners should always award full marks if deserved, i.e. if the answer matches the mark scheme. Examiners should also be prepared to award zero marks if the candidates response is not worthy of credit according to the mark scheme. Where some judgement is required, mark schemes will provide the principles by which marks will be awarded and exemplification may be limited. When examiners are in doubt regarding the application of the mark scheme to a candidates response, the team leader must be consulted. Crossed out work should be marked UNLESS the candidate has replaced it with an alternative response. Mark schemes will indicate within the table where, and which strands of QWC, are being assessed. The strands are as follows: i) ensure that text is legible and that spelling, punctuation and grammar are accurate so that meaning is clear ii) select and use a form and style of writing appropriate to purpose and to complex subject matter iii) organise information clearly and coherently, using specialist vocabulary when appropriate

Using the Mark SchemeExaminers should look for qualities to reward rather than faults to penalise. This does NOT mean giving credit for incorrect or inadequate answers, but it does mean allowing candidates to be rewarded for answers showing correct application of principles and knowledge. Examiners should therefore read carefully and consider every response: even if it is not what is expected it may be worthy of credit. The mark scheme gives examiners: an idea of the types of response expected how individual marks are to be awarded the total mark for each question examples of responses that should NOT receive credit. / means that the responses are alternatives and either answer should receive full credit. ( ) means that a phrase/word is not essential for the award of the mark, but helps the examiner to get the sense of the expected answer. Phrases/words in bold indicate that the meaning of the phrase or the actual word is essential to the answer. ecf/TE/cq (error carried forward) means that a wrong answer given in an earlier part of a question is used correctly in answer to a later part of the same question. Candidates must make their meaning clear to the examiner to gain the mark. Make sure that the answer makes sense. Do not give credit for correct words/phrases which are put together in a meaningless manner. Answers must be in the correct context. Quality of Written Communication Questions which involve the writing of continuous prose will expect candidates to: write legibly, with accurate use of spelling, grammar and punctuation in order to make the meaning clear select and use a form and style of writing appropriate to purpose and to complex subject matter organise information clearly and coherently, using specialist vocabulary when appropriate. Full marks will be awarded if the candidate has demonstrated the above abilities. Questions where QWC is likely to be particularly important are indicated (QWC) in the mark scheme, but this does not preclude others.

Section AQuestion Number 1(a) Question Number 1(b) Question Number 2 Question Number 3 Question Number 4 Question Number 5 Question Number 6(a) Question Number 6(b) Question Number 6(c) Question Number 7 Question Number 8 Question Number 9 Correct Answer A Correct Answer C Correct Answer B Correct Answer D Correct Answer D Correct Answer B Correct Answer C Correct Answer B Correct Answer D Correct Answer A Correct Answer C Correct Answer B Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1

Question Number 10 Question Number 11 Question Number 12(a) Question Number 12(b) Question Number 12(c) Question Number 12(d) Question Number 13 Question Number 14

Correct Answer C Correct Answer D Correct Answer B Correct Answer A Correct Answer C Correct Answer A Correct Answer A Correct Answer A

Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1 Mark 1

Section BQuestion Number 15(a) Acceptable Answers (It has) three (moles of) COOH groups / three (moles of) carboxylic acid groups / three (moles of) protons /three (moles of) H+ /it is tribasic / three acid groups/ three (moles of) replaceable hydrogens/triprotic ALLOW Three acid groups Reject carbonyl/carboxylate Mark 1

Question Number 15(b)(i)

Acceptable Answers FIRST, CHECK THE FINAL ANSWER IF answer = +546 (J mol1 K1) award 2 marks 546 (J mol1 K1) scores (1) as sign omitted) (S system =)[200.5 + (3 x 213.6) + (3 x 69.9)] [199.9 + (3 x 101.7)] (1) = [+1051] [+ 505] = +546 (J mol1 K1) (1) Allow + 0.546 kJ mol1 K1 2nd mark is CQ on entropy values used for example EITHER Omission of factor of x3 for some or all substances in the equation OR The use of one incorrect entropy value(s) from the data book OR One missing value Note If two or more of the above three errors are made together, (0) awarded. IGNORE sf except 1 sf

Reject

Mark 2

Incorrect units (no 2nd mark)

Question Number 15(b)(ii)

Acceptable Answers First mark Gas formed (from solid) OR Liquid formed (from solid) OR Gas and liquid formed (from solid) (1) Second mark EITHER More moles of product than reactants / more moles formed OR 4 mol (of reactants) to 7 mol (of products) OR 4 molecules to 7 molecules NOTE: If specific numbers are stated, these must be correct (ie 47) OR Increase in disorder / increase in ways of arranging particles (1) IGNORE entropy increases NOTE: Both points may be made in the same sentence

Reject

Mark 2

Just more product / more particles formed 2 substances going to 3 substances

Question Number 15(b)(iii)

Acceptable Answers (S surroundings

Reject

Mark 2

=) H OR 70000 T 298 = = (1) 234.8993289 Incorrect rounding (e.g. 235 J mol1 K1 (1) 234 / 234.89) no 2nd mark 70 298 (1) = 0.235 kJ mol1 K1 (1)

OR (S surroundings =) H OR T

IGNORE sf except 1 sf NOTE: Correct units are required for the award of the second mark +235 with units scores (1)

+235 with no units (0) overall

Question Number 15(b)(iv)

Acceptable Answers (S = S system + S surroundings) = (+546) + (235) = (+)311 (J mol-1 K1) OR = (+)0.311 kJ mol-1 K1 CQ on (i) and (iii)total

Reject

Mark 1

Incorrect units

IGNORE sf except 1 sf Question Number 15(b)(v) Acceptable Answers Positive so feasible / spontaneous / will occur / reaction goes / reacts (at 298 K) NOTE: LOOK BACK at answer to (b)(iv) IF answer to (b)(iv) has a positive sign (the + sign can be stated or implied) THEN ALLOW JUST feasible / spontaneous / will occur / reaction goes / reacts (at 298 K) Mark CQ on sign of answer to (iv) Reject Mark 1

(Total 9 marks)

Question Number 16(a)(i)

Acceptable Answers Kw = [H+] x [OH] OR = [H3O+] x [OH] Kw State symbols are not required IGNORE any incorrect state symbols Acceptable Answers FIRST, CHECK THE FINAL ANSWER IF answer pH = 11.875 / 11.88 / 11.9 /12 award 2 marks IGNORE sf except 1 sf = 1.00 x 1014 0.00750 = 1.3333 x 1012 = 1.33 x 1012 (1) (mol dm3) ALLOW first mark for just [H+] = Kw [OH] Kw [OH] pH = log10 [H+] = 11.875 = 11.88 / 11.9 (1) (1) (1) [H+] =

Reject Inclusion of [H2O]

Mark 1

Question Number 16(a)(ii)

Reject

Mark 2

OR pOH = log10 [OH] = 2.12 pH = pKw pOH pH = 11.88 / 11.9

Second mark only awarded CQ if pH between 8 and 14

Question Number 16(b)

Acceptable Answers First mark Moles NaOH = 0.00750 x 20.0 1000 = 1.50 x 104 (mol) (1) (Since HCOOH : NaOH ratio is 1:1) Second mark [HCOOH(aq)] = 1.50 x 104 0.0250 OR = 1.50 x 104 x 1000 25.0 (1) (= 6.00 x 103 mol dm3) ALTERNATIVE APPROACH: Use of an expression such as 0.00750 x 20.0 = 25 x y y = 0.00750 x 20.0 25 (1)

Reject

Mark 2

(1) Reject Mark 2 not easily dissociated

Question Number 16(c)(i)

Acceptable Answers (Weak) dissociates / ionizes to a small extent OR dissociate / ionizes partially OR dissociates / ionizes incompletely OR does not fully dissociate / ionize OR forms an equilibrium when reacted with water (1) (Acid) proton donor ALLOW proton donator OR produces / releases H+ ions OR produces / releases H3O+ ions Ignore reference to typical acid reactions

(1)

Question Number 16(c)(ii)

Acceptable Answers (Ka =) [HCOO] [H+] [HCOOH] State symbols are NOT required IGNORE any incorrect state symbols

Reject [H+]2 [HCOOH] Inclusion of [H2O] (Ka = )

Mark 1

Question Number 16(c)(iii)

Acceptable Answers IGNORE sf except 1 sf THROUGHOUT FIRST, CHECK THE FINAL ANSWER IF answer Ka = 1.59 x 10-4 (mol dm-3) award the first two 2 marks [H+] (= 10-pH = 10-3.01) = 9.77 x 10-4 (mol dm-3) (1) Ka Ka = [H+]2 [HCOOH]

Reject

Mark 4

Assumption 1 [H+] = [HCOO] OR no H+ from the (ionization of) water OR H+ only from the acid

= (9.77 x 10-4)2 6.00 x 103 = 1.59 x 10-4 (mol dm-3) (1)

If incorrect units max 1

(1)

Assumption 2 Ionization of the (weak) acid is negligible / very small / insignificant OR [HCOOH]initial x = [HCOOH]eqm OR [HCOOH]eqm = [HCOOH]initial OR [HCOOH]eqm = 6.00 x 103 (mol dm3) OR [H+]