Mark Scheme (Results) Summer 2010

Transcription

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

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3 IGCSE CHEMISTRY 4335/F SUMMER 200 SECTION A a i M neutron M2 proton M3 electron ii M nucleus iii M 2 iv M 5 v M 2.3 Accept any punctuation (eg, / )) or none b i M helium / beryllium / magnesium / calcium / strontium / barium / radium / He / Be / Mg / Ca / Sr / Ba / Ra ii M hydrogen / helium / H / He Accept H 2 c it has isotopes / atoms have different numbers of neutrons / it Reject different numbers of protons / is an average electrons

4 2 a i M air / atmosphere re any reference to method ii M natural gas / North Sea gas / hydrocarbons / named fraction / Ignore methane water / steam b i M3 iron / Fe Ignore reference to oxide(s) / oxidation states II and III ii M M iii M cross in box 3 M2 cross in box 4 M3 cross in box 5

5 3 a M phosphorus Accept answers in either order M2 potassium Ignore symbols b i M cross in box ii M cross in same box as in bi Consequential marking from bi

6 4 a M denser than air / greater molar mass than air or nitrogen or oxygen Accept heavier than air/nitrogen/oxygen b M limewater / aqueous calcium hydroxide / Ca(OH) 2 (aq) Accept (aq) / solution / dissolved in water as equivalent to aqueous M2 milky / cloudy /chalky / white precipitate / white solid Ignore bubbles c M copper(ii) carbonate copper(ii) oxide + carbon dioxide Both (II) needed Reject any other substances Ignore heat d M green Ignore qualifiers such as light / dark M2 black Reject all other colours

7 5 a M cross in box M2 cross in box 4 b M filter or filtration / centrifuge and decant Accept description of process Reject any wrong method c M wash (with water) / add water and filter Accept description of process M2 dry / heat / warm / evaporate / leave in warm place / spread Accept description of process onto filter paper / place in (warm) oven Ignore wrong consequence (eg heat to remove sodium nitrate) If M and M2 in wrong order, award/2 Reject any wrong method in both M and M2

8 6 a M covalent b M low M2 weak If high given for M, then accept strong M3 molecules Mark b independently except that if high given for M, then accept strong for M2 c M shared pairs of electrons between O and both H atoms Electrons can be shown as dots / crosses / e / M2 two electrons in O inner shell AND four more electrons in O outer shell AND no extra electrons in H any combination of these Accept these electrons paired or unpaired M2 dependent on M d i M blue Ignore qualifiers such as light / dark Reject all other colours M2 white / grey / pale(r) blue Accept all combinations of these Reject all other colours ii M anhydrous copper(ii) sulphate (II) not needed iii M becomes blue / heat produced / temperature rises / forms If different colour given in di(m), accept this hydrated copper(ii) sulphate / goes back to original colour colour here

9 7 a i M propene / propylene Accept prop--ene ii M yellow / orange / brown Accept any combination of these colours Reject red M2 (goes) colourless / decolourised Ignore clear Ignore discoloured Do not award mark for single colour if not clear whether start or finish b i M (contains) hydrogen and carbon / H and C (atoms) Reject molecules / ions M2 only Accept other words with equivalent meaning, such as purely / solely / entirely Award M2 only if correct elements mentioned in M ii M only single bonds / no double bonds / no multiple bonds iii M double bond between two carbon atoms M2 each carbon bonded to two hydrogen atoms M2 dependent on M c M cross in box M2 cross in box 5 d M C 2 H 4 / CH 2 CH 2 / CH 2 =CH 2 Accept in either order M2 H 2 O Ignore state symbols Award mark for both correct formulae but incorrect coefficients Accept H 4 C 2 and OH 2 SECTION A TOTAL: 55 MARKS

10 SECTION B 8 a i M bubbles / fizzing / effervescence / metal gets smaller / white Ignore metal dissolves / gas produced trail Reject all answers in a(ii) ii M melts / forms a ball / darts / moves (on surface) / floats Ignore reference to flames Reject all answers in a(i) b i M calcium hydroxide ii M NaOH c M hydrogen / H 2 Ignore H M2 (squeaky) pop with burning splint /burns with a (squeaky) pop Accept other words such as explosion / lighted spill or taper Reject glowing splint Ignore references to air/splint extinguished No CONSEQ from wrong gas d i M blue / purple Ignore qualifiers such as light / dark / bright M2 OH / hydroxide Ignore hydroxyl ii M yellow / orange Ignore qualifiers such as light / dark / golden / bright Reject all other colours

11 9 a M hydrogen peroxide M2 manganese(iv) oxide / manganese dioxide b M (gas) syringe c M catalyst / to speed up the reaction / lower activation energy d i M (s) for both PbS and PbSO 4 M2 (aq) for H 2 O 2 and (l) for H 2 O ii M PbS / lead sulphide / sulphide ion / S 2 / sulphur in lead Ignore oxidation numbers if given sulphide M2 gains oxygen/o/o 2 increase in oxidation state only award if M correct or sulphur ignore loss of electrons e i M S + O 2 SO 2 Ignore state symbols Accept S 2 or S 8 ii M acidic / (forms) H + (ions) / sulphurous acid / sulphuric(iv) acid Reject sulphuric acid / sulphuric(vi) acid iii M orange M2 green Accept blue-green

12 0 a M electron transfer All marks can be scored from suitably M2 from magnesium/mg to chlorine/cl annotated diagrams M3 Mg loses two electrons and (each) Cl gains one electron Award 0/3 if any reference to sharing electrons Ignore covalent M3 dependent on M2 b M magnesium / Mg M2 loss of electrons / increase in oxidation state Ignore number of electrons M2 independent of M c M + and ions / oppositely charged ions / Mg 2+ and Cl Need idea of + and - charge M2 strong (electrostatic) attractions (within lattice) accept strong (ionic) bonds reject covalent bonds / molecular attraction M3 lot of energy needed to overcome attractions / break bonds / separate ions Do not accept loosening bonds Ignore hard to break any mention of intermolecular or intramolecular loses M and M2 So strong intermolecular forces need lots of energy to overcome scores M3

13 a i M fractional distillation / fractionation ii M crude oil heated M given even if describe laboratory process. Only M possible if describe lab process or mention cracking/breaking bonds M2 (vapour) passed into column/tower If crude oil heated in fractionating column, then give only mark for M and M2 M3 fractions collected at different heights M4 correct reference to boiling point / molecular size / Do not award if specified temperature temperature gradient/hot at bottom cooler at top gradient is wrong way round All marks can be gained from suitable diagram b i M bitumen ii M gasoline iii M bitumen iv M refinery gases Accept answers in either order M2 fuel oil Accept naphtha in place of either c M oxygen Ignore air M2 carbon dioxide Accept answers in either order M3 water Accept steam in place of water All marks in c are independent Ignore heat

14 d i M C n H 2n+2 Accept other letters/symbols such as x accept C n H 2(n+) ii M same/similar chemical properties / same functional group reject trend in chemical properties M2 gradation in physical properties / gradation in specified physical property (eg boiling point) reject same/similar physical properties M3 neighbouring members differ by CH 2 Ignore references to general formula and 2 references to saturation/unsaturation/specific functional group Accept any two for mark each SECTION B TOTAL: 45 MARKS PAPER TOTAL: 00 MARKS

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