Mark Scheme (Results) November 2010

Transcription

1 Mark Scheme (Results) November 200 IGCSE IGCSE Chemistry (4335) Paper 2H Edexcel Limited. Registered in England and Wales No Registered Office: One90 High Holborn, London WCV 7BH

2 Edexcel is one of the leading examining and awarding bodies in the UK and throughout the world. We provide a wide range of qualifications including academic, vocational, occupational and specific programmes for employers. Through a network of UK and overseas offices, Edexcel s centres receive the support they need to help them deliver their education and training programmes to learners. For further information, please call our GCE line on , our GCSE team on , or visit our website at If you have any subject specific questions about the content of this Mark Scheme that require the help of a subject specialist, you may find our Ask The Expert service helpful. Ask The Expert can be accessed online at the following link: Alternately, you can speak directly to a subject specialist at Edexcel on our dedicated Science telephone line: (If you are calling from outside the UK please dial and state that you would like to speak to the Science subject specialist). November 200 All the material in this publication is copyright Edexcel Ltd 200

3 IGCSE CHEMISTRY 4335/2H NOVEMBER 200 SECTION A Question Mark a M ºC Units required M (atm(ospheres)) Units not required M3 iron / Fe (catalyst) Ignore iron oxide Ignore oxidation states b M condensation / liquefaction / gas liquid c i M NH 3 + HNO 3 NH 4 NO 3 Reactants = 2 Products = Award if both reactant and product formulae correct but unbalanced ii M fertiliser / explosives

4 Question Mark 2 a M copper less reactive than iron / iron more reactive than copper Do not accept iron(ii) in place of iron or copper(ii) in place of copper Accept negative (copper is not more reactive than iron) Accept iron is a better oxidising agent than copper / copper ions are a better reducing agent that iron ions. b M Copper((II)) / Cu 2+ /Cu(H 2 O) 2+ 6 / hexa aqua copper(ii) c M copper / Cu d M iron is formed/ iron displaced by zinc e M zinc / Zn f M green precipitate Ignore qualifiers such as dark/light/sludge Reject all other colours Accept solid / suspension M2 iron(ii) hydroxide / Fe(OH) 2 Accept ferrous hydroxide or formula of complex ion

5 Question Mark 3 a i M contain hydrogen and carbon only Reject hydrogen or carbon molecules/ions ii M no double bond(s) / only single bonds (between carbon Accept no multiple bonds / no C=C atoms) b i M alkane ii M C n H 2n+2 Accept any other symbol in place of n n and 2n+2 must be clearly smaller than C and H. iii M Similar/same chemical properties M2 gradation in physical properties (or specified physical Any two for each 2 property such as increase in boiling point ) M3 neighbouring members (formulae) differ by CH 2 c M H H H All bonds/atoms must be shown. H C C C H H H H d i M (compounds with) same molecular formula Reject atoms/elements/ions M2 (but) different structures/structural formulae/displayed formulae ii M butane OR (2-)methylpropane M2 H H H H H H H H C C C C H H H H H H C C C H H H H C H H e M methane + oxygen carbon dioxide + water/steam Reactants = 2

6 M2 Products = If air given in place of oxygen, products mark can still be awarded Award M and M2 independently

7 Question Mark 4 a M () H 2 Ignore state symbols M2 () hydrogen M3 (3) H 2 O + CO 2 Ignore state symbols Accept answers in either order M4 (3) water Accept answers in either order M5 (3) carbon dioxide b M effervescence / fizzing / bubbles Ignore gas formed c M white precipitate/solid/suspension M2 barium sulphate Question Mark 5 a i M electron transfer M2 from magnesium to fluorine M3 magnesium loses 2 electrons and (each) fluorine gains electron Ignore covalent Electron sharing = 0 M2 F ii M Mg 2+ Accept answers in either order b i M carbon / graphite / C ii M Melt / fused Ignore dissolved in water iii M (silvery liquid) lead if M and M2 wrong way round then M2 (brown gas) bromine give mark, but do not award M3 M3 (silvery liquid) or cathode AND (brown gas) + or anode

8 Question Mark SECTION B 6 a M acid rain / kills fish/trees / damages buildings/statues / corrodes specified metal object / leaches minerals from soils Not corrodes/erodes for buildings/statues Ignore kills animals Accepts harms for kills b i M (pure) copper / stainless steel ii M Copper((II)) sulphate Ignore references to acid c M Electrical wiring Overhead (power) cables (Water) pipes Coins (bottom of) saucepans Accept any other suitable property M2 related property: Electrical wiring electrical conductor/malleable/ductile Overhead power cables - electrical conductor / malleable /ductile Water pipes unreactive / does not corrode / ductile /malleable (bottom of) saucepans heat conductor/unreactive d i M to burn/react with coke/carbon/c M2 to produce heat / make it hot / increase the temperature ii M limestone/calcium carbonate (thermally) decomposes Accept formula in place of name M2 forms calcium oxide Accept formula in place of name M3 (calcium oxide) reacts with/neutralises silicon dioxide Accept formula in place of name M4 forms calcium silicate/slag Accept formula in place of name CaCO 3 CaO + CO 2 scores M and M2 CaO + SiO 2 CaSiO 3 scores M2, M3 and M4 CaCO 3 + SiO 2 CaSiO 3 + CO 2

9 scores for slag formula iii M carbon/c oxidised/gains oxygen/increases oxidation number M2 Iron((III)) oxide/fe 2 O 3 / iron in iron oxide / iron(iii) reduced/loses oxygen iron in iron oxide / iron(iii) decreases oxidation number / gains electrons If neither M nor M2 scored, award mark for idea of both oxidation and reduction occurring

10 Question Mark 7 a i M same number of electrons in outer energy level/shell Accept all/both have one electron in outer energy level/shell ii M 2Rb + 2H 2 O 2RbOH + H 2 Formulae = 2 M2 Balancing = iii M Flame/ explosion / moves/fizzes faster ignore references to colour of flame b M 23 M 2 M 3 48 c i M atoms with same atomic number/same number of protons Ignore same number of electrons OR atoms of same element Reject different numbers of electrons M2 different mass number / different number of neutrons If no mention of atoms, then max ii M 87 Rb percentage = 27.8 M2 ( ) + ( ) CQ on M M CQ on M2 Answer must be to dp Correct answer scores 3. d i M electrons (can) move/are mobile (throughout structure) Ignore sea of/delocalised/free electrons Reject ions moving ii M atoms/ions in layers/rows M2 layers/rows slide/move over each other Marks can be awarded for explanation based on non-directional bonding meaning atoms/ions can move without the need to break bonds

11 Question Mark 8 a i M MgO + H 2 O Mg(OH) 2 Mg(OH) 2 formula = 2 M2 Rest correct = ii M 7 < value M2 (weakly) alkaline / hydroxide / OH Ignore base b i M M2 CaCO 3 + 2HCl CaCl 2 + H 2 O + CO 2 Formulae = Balancing = 2 Ignore state symbols ii M carbonic (acid) iii M magnesium carbonate / MgCO 3 Accept Mg(HCO 3 ) 2 or magnesium hydrogencarbonate c M bright/white/dazzling light/flame M2 white solid/smoke/ash d i M answer in range 20-2 ii M (i) 5 / answer in range -.05 CQ on (i) 00 M2 M / answer in range Cq Accept or more sig fig answer cq on (i) Correct final answer scores 2 marks iii M (ii) 2 / answer in range Accept answer to or more sig figs iv M (iii) 24 M2 answer in range

12 Question Mark 9 a M (crude oil) heated / vaporized Reject if heated in fractionating tower M2 cooler at top / hotter at bottom / idea of temperature gradient Accept gases cool as they rise M3 fractions condense at different heights/levels M4 fractions have different boiling points/ranges/(molecular) size/mass Any three for each If lab process described, scores M only b i M product with alkene formula ( 20 C atoms) M2 second product shown and balances M2 dep on M ii M distillation/crude oil produces more long-chain / fewer shortchain hydrocarbons/fractions (than there is demand for) M2 short chains more useful/in greater demand/used as fuels / converse 2 c i M correct repeat unit M2 continuation bonds DEP on M ii M chloroethene / vinyl chloride M2 H C=C H H Cl 3

13 d i M condensation / polyamide ii M alternating square and circle with continuation bonds At least one square and one circle needed (continuation may be incorrect) M2 correct link between square and circle Accept -NHCO- / -HNOC- Ignore continuation section M3 correct continuation Needs to be correct at both ends iii M hydrogen chloride / HCl Reject hydrochloric acid

14 Question Mark 0 a M weak forces / van der Waals' forces / hydrogen bonds Accept London / dispersion forces M2 intermolecular / between molecules M3 need little energy to overcome / break Accept easily broken Any reference to ions / breaking covalent bonds / bonds within molecules = 0 b M bubbles / fizzing / effervescence c i M 6 69 M2 04 CQ on M only if 69 transcription error or multiplication by 3 instead of 6 Correct answer scores 2 marks, -04 scores ii M (3 5) M2 397 Ignore sign Correct answer scores 2 Max if one error (such as failing to x 3 or incorrect transcription of bond energy) if miss out one of the bonds, then zero. iii M (i) (ii) / 383 CQ d i M three shared pairs of electrons Accept any recognisable symbol for electrons M2 other electrons correct DEP on M Ignore inner shells ii M (electrons) attracted to both nuclei Attraction to both nuclei must be implied e M Division by A r N H P O 28.2 = = = = M2 Simplification of ratio CQ on (i) 2.0 = 3 8. = = 2.68 = 4

15 M3 N 3 H 2 PO 4 Accept (NH 4 ) 3 PO 4 if obtained with some working CQ on M2 but only if attempt has been made to simplify ratio, can not just use moles from (i) PAPER TOTAL: 20 MARKS

16 Further copies of this publication are available from International Regional Offices at For more information on Edexcel qualifications, please visit Alternatively, you can contact Customer Services at or on Edexcel Limited. Registered in England and Wales no Registered Office: One90 High Holborn, London, WCV 7BH