Mark Scheme (Results) Summer IAL Chemistry (WCH01/01)

Transcription

1 Scheme (Results) Summer 05 IAL Chemistry (WC0/0)

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3 General ing Guidance All candidates must receive the same treatment. Examiners must mark the first candidate in exactly the same way as they mark the last. 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 candidate s 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 candidate s response, the team leader must be consulted. Crossed out work should be marked UNLESS the candidate has replaced it with an alternative response. 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

4 Section A (multiple choice) D B 3 C 4 D 5 D 6 D 7 C 8 D 9 D 0 B A A

5 3 C 4 A 5 B 6 C 7 C 8 C 9 A 0 A TOTAL F SECTION A = 0 MARKS

6 Section B (a)(i) Alkane(s) IGNE Any references to branched / aliphatic / hydrocarbons (a)(ii),3-dimethyloctane IGNE Incorrect or missing punctuation (a)(iii) st mark: 3 (Isomers) A and C NOTE If no isomers or isomers other than A & C have been chosen, then award one mark max providing both nd and 3 rd marking points are evident. Different chemical formulae nd mark: (They/A and C) have the same molecular formula / C 0 / same number of C and (atoms) 3rd mark: (They/A and C) have different structural formulae/displayed formulae / skeletal formulae / different structures/different arrangement of atoms IGNE Any references to in space / spatial Any references to names Any references to general formulae

7 (a)(iv) C 4 st mark: C nd mark: 4 (b)(i) A B ALLOW lower case letters IGNE any names or formulae (b)(ii) C D ALLOW lower case letters IGNE any names or formulae

8 (c) Any one of: (It improves engine performance by) Promoting efficient combustion Allowing smoother burning Increasing octane number Reduces knocking / prevents knocking Pre-ignition being less likely Being (more) efficient (fuels) Better burning / fuels easier to burn Combusting more easily Improving combustion / complete combustion Burns more cleanly More miles per gallon IGNE any references to energy density / boiling temperature / volatility

9 (d) [FIRST, check the answer on the answer line IF answer = (kj kg ) award (3) marks] 3 st two marks 000 x x NOTE: second mark in both cases dependent on first mark unless one minor transcription error in first mark e.g. use of 0 rather than 70 3 rd mark = = Answer must be to sf Ignore signs and / or incorrect units at any stage 48 scores () scores scores (0) even if rounded to SF (Total for = 3 marks)

10 (a)(i) ALLOW = (a)(ii) 5 ALLOW 5 = 5 (a)(iii) 6 6 / (a)(iv) ALLOW = 7

11 (b)(i) (The energy change / enthalpy change that accompanies / energy released / enthalpy released) the formation of one mole of a(n ionic) compound ALLOW as alternative for compound: lattice /crystal / substance / solid / product Energy / enthalpy required / used molecule no st mark from its gaseous ions NOTE one mole of gaseous ions scores max (ie nd mark only available) gaseous atoms no nd mark IGNE References to constituent elements References to standard conditions ALTERNATIVE RESPONSE If no mark(s) already awarded from above, can answer by giving:- energy change / enthalpy change per mole Sr + (g) + Cl (g) SrCl (s) ALLOW Any correct generic equation with state symbols included

12 (b)(ii) [FIRST, check the answer on the answer line IF answer = 53 (kj mol ) then award () marks, with or without working] st : = = [ ] 7 = 89 [ ( x ) + ( x 349)] nd : 7 = 53 (kj mol ) NOTE: The following answers score mark with or without working +53 (kj mol ) 03 (kj mol ) 50 (kj mol ) 380 (kj mol ) NO OTER TEs are allowed on an incorrect expression involving 7

13 *(c) (Lattice energy of MgF more exothermic than that of NaF because) 3 st mark: Mg + is smaller (than Na + ) ALLOW Magnesium / Mg is smaller (than sodium / Na) No st mark if only mention Mg atom or atomic radius nd mark: Mg + higher charge / higher charge density (than Na + ) ALLOW Any reference to Mg + and Na + in answer for the nd mark, unless nuclear charge mentioned Mg + higher nuclear charge 3rd mark: (So electrostatic forces of) attraction between ions stronger in MgF (than in NaF) ALLOW Stronger ionic bonds in MgF / stronger ionic bonding in MgF reverse arguments (Total for = marks)

14 3(a) C n n ALLOW Letters other than n ALLOW: (partially) displayed or skeletal formulae throughout Q3(b) IGNE: additional incorrect non-organic products 3(b)(i) C 3 C 3 C 6 3(b)(ii) ClC C Cl / C ClC Cl C 4 Cl ONLY PENALISE ONCE ONLY in (b)(iii) & (b)(iv) TE CONNECTIVITY BETWEEN C and O if CLEARLY a C to covalent bond has been drawn 3(b)(iii) OC C O / C OC O C 6 O / OC C O 3(b)(iv) OC C Br / C OC Br BrC C Br / C 5 OBr / C 4 Br

15 PENALISE USE OF Br instead of Cl once only in parts (c)(i) & (c)(ii) PENALISE missing atoms from displayed formulae once only in parts (c)(i) & (c)(ii) 3(c)(i) Cl C C C (Major product) C C C Cl (Minor product) Both DISPLAYED structures, with all bonds and atoms shown but in the wrong boxes scores PENALISE C 3 not fully displayed ONCE only So C 3 C(Cl)C 3 and C 3 C C Cl scores

16 3(c)(ii) 3 C 3 3 C C C Cl both arrows 3 C C C carbocation 3 C + Cl C C C C (:)Cl attack of chloride ion st mark: Curly arrow from C=C to (in Cl) AND curly arrow from bond in Cl to the Cl (dipole not reqd) Curly arrows must start from the bonds NOT the atoms Cl Full + and charges on Cl Incorrect polarity on Cl nd mark: Structure of correct secondary carbocation 3rd mark: Curly arrow from anywhere on the chloride ion (including the minus sign) towards the C+ on the carbocation NOTE: The chloride ion must have a full negative charge, but the lone pair of electrons on the Cl need not be shown Extra / spare bond dangling from the C+ carbon δ- on chloride ion instead of Cl ALLOW: TE on major product given in (c)(i) Skeletal formulae can be used the three points independently

17 3(d)(i) 3 C C C nc 3 6 n TWO n in the equation and a correct formula (molecular or structural) for propene on the left-hand side of the equation One correct repeating unit, with the methyl branch shown ALLOW C 3 fully displayed or just as C 3 BOT continuation bonds (with or without bracket shown) If C=C bond left in polymer on righthand side, then max the three points independently

18 3(d)(ii) Non-biodegradable IGNE References to toxicity of poly(propene) / flammability IGNE Litter / pollution / waste of resources / costs ALLOW People are reluctant to recycle armful to marine life / harmful to wildlife References to landfill References to incineration producing toxic fumes/toxic gases / CO / Greenhouse gases References to use of energy/fuel used in transport (of waste) It takes a long time to degrade

19 3(e)(i) 3C(s) + 3 (g) f C 3 6 (g) (+4½O ) (+4½O ) 3CO (g) and 3 O(l) Both arrows in the correct direction AND 3CO and 3 O in lowest box IGNE state symbols, even if incorrect IGNE extra O molecules in box or alongside arrows 3(e)(ii) st mark ( 394 x 3) + ( 86 x 3) = 040 (kj mol ) nd mark: f = 040 ( 058) = (+)8 (kj mol ) NOTE: The following answers score mark with or without working 8 (kj mol ) (+)378 (kj mol ) (+)806 (kj mol ) (+)590 (kj mol ) 4098 (kj mol ) IGNE units even if incorrect (Total for 3 = 7 marks

20 4(a) F(g) F + (g) + e ( ) Electron affinity equation (0) F(g) e ( ) F + (g) overall Species State symbols IGNE Any state symbols on electrons Equations with F (g) score (0) overall nd mark is dependent on the first NOTE: F(g) + e ( ) F + (g) + e ( ) Use of Fl max 4*(b) st mark: of protons increases / increasing nuclear charge / increasing effective nuclear charge 3 IGNE Just the atomic number increases nd mark: Same shielding / same number of (occupied) shells / electron removed from the same shell / atomic radius decreases Shielding increases (0) for nd mark 3rd mark: Greater (electrostatic) attraction between nucleus / protons and (outermost) electron

21 4(c)*(i) For aluminium st mark: (Electron lost from) (3)p-subshell / (3)p-orbital ALLOW Correct electron configuration for Al: s s p 6 3s 3p or [Ne]3s 3p or drawn as electrons-inboxes Mention of p, no st mark NOTE First mark must refer to aluminium nd mark: at higher energy / further from the nucleus / (more) shielded (by 3s) Magnesium electron is at lower energy / closer to the nucleus / less shielded IGNE References to stability of 3s or full s- orbitals / full s sub-shell in Mg

22 4(c)*(ii) For sulfur st mark: (Electron lost from a) pair of electrons / an orbital with electrons (spin-) paired / a full (p) orbital ALLOW Mention of (3)p 4 Correct electron configuration for S:s s p 6 3s 3p 4 or [Ne]3s 3p 4 or drawn as electrons-inboxes nd mark: (increase in) repulsion (allows e to be removed more easily) If no correct reference to Sulfur, then allow one mark for P (atom) has half-filled p sub-shell / p 3 (arrangement) is stable.

23 4(d)(i) (Al) (Si) (P) (S) high high low low Four correct () Three correct 4(d)(ii) (Na) (Al) (Si) (P) (S) giant (giant) giant giant molecular molecular ALLOW giant molecular for Si ALLOW simple molecular for P and/or S Five correct () Four correct 4(d)(iii) (Na) (Al) (Si) (P) (S) high (high) high X low low All four must be correct IGNE Any word written over X in the Si box

24 4(e)(i) (.76 ) = 0.(0) (mol) 3.0 4(e)(ii) Moles = ½ x mol Na Volume = 0.06(0) x 4 =.44 (dm 3 ) ALLOW ECF from moles of Na in (e)(i) ALLOW Both marks if answer given 440 cm 3 Correct answer, no working scores () NOTE: The following answers score mark with or without working.88 (dm 3 ) / 880 cm (dm 3 ) / 5760 cm 3 owever, check as.88 could score as a TE of 0.4 mol from (e)(i) IGNE SF except SF

25 4(e)(iii) st mark: Moles NaO = moles of Na Can be implied by use of value from (e)(i) nd mark: ( 0. ) = 0.4(0) (mol dm 3 ) ALLOW TE from moles of Na in (e)(i) Correct answer, no working scores () IGNE SF except SF No nd mark if give wrong units, e.g mol/dm 3 dm 3 /mol NOTE: TE from first mark to second mark only if answer from (e)(i) has been used in some way e.g. answer to (e)(i) would not score mark, but could then be used to score mark as a TE (Total for 4 = 9 marks) TOTAL F SECTION B = 60 MARKS TOTAL F PAPER = 80 MARKS

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