Qualitative Analysis: Test for Ions

Transcription

1 Qualitative Analysis Test for Ions Mark Scheme 1 Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Qualitative Analysis: Test for Ions Booklet Mark Scheme 1 Time Allowed: 53 minutes Score: /44 Percentage: /100

2 1(a)(i) A calcium ion, Ca 2+ 1(a)(ii) A description including Maximum 1 mark if bubbles / fizzing / effervescence also mentioned white precipitate/ppt/ppte/solid Ignore colour of solution Ignore cloudy Ignore off white/milky Allow crystals Ignore powder Ignore name of precipitate 1(b) B lead chloride 1(c)(i) (barium chloride (aq) + sodium sulfate (aq) ) sodium chloride (aq) + barium sulfate (s) sodium chloride Allow NaCl Do not allow sodium chlorine (sodium chloride) (aq) and barium sulfate (s) both state symbols matched to the correct product Accept BaSO 4 for barium sulfate Accept (aq) if sodium chlorine given Do not allow (solid) Do not allow (AQ)

3 1(c)(ii) An explanation linking {barium sulfate/it} does not dissolve into the blood(stream) {barium sulfate/it} is {insoluble / does not dissolve} so it {cannot enter/cannot mix with/is not absorbed} into the {blood(stream)/body} or it passes through the body (unchanged) Allow barium is insoluble / does not dissolve Ignore barium sulfate is a precipitate Ignore it cannot be digested

4 2(a)(i) C iodide, I - 2(a)(ii) A description linking two points from flame test / description of flame test mentioning in flame sodium gives a yellow flame potassium gives a {lilac/purple/violet} flame description can be using (nichrome) wire or damp splint Ignore: hold over/ around/under/above flame Ignore: yellow-orange, orange or any other colour 2(b)(i) A description linking blue precipitate / solid Marked independently. allow appropriate qualifiers: e.g. light blue but not other colours eg green-blue allow ppt If further, incorrect observations given, use list principle

5 2(b)(ii) Cu OH - Cu(OH) 2 (3) allow multiples accept Cu 2+ (OH - ) 2 (3) Identifies Cu 2+ on LHS and Cu(OH) 2 on RHS in equation format OH - formula on LHS These two marks are independent and can be scored even if additional ions, correct or incorrect, are given allow Cu ++ / Cu +2 reject incorrect symbols such as cu 2+, Oh - etc. ignore: state symbols allow = instead of balancing correct symbols This mark is only awarded for a fully correct ionic equation with no additional ions

6 3(a)(i) A description linking add dil nitric acid then silver nitrate solution allow silver nitrate solution alone reject if wrong reagent / acid mentioned yellow precipitate/solid colour and form both required reject cream reject yellow-orange 3(a)(ii) A description linking add to sodium hydroxide (solution) and warm test gases with (moist ) (red) litmus paper (litmus paper) turns blue allow sodium hydroxide (solution) alone allow heat solid alone allow Universal Indicator paper/ ph paper allow correct colour change for named indicator (3) 3(a)(iii) C iron(iii), Fe 3+

7 3(b) A description to include white {precipitate/solid} with calcium (ions) white {precipitate/solid} with aluminium (ions) (precipitate/solid) dissolves in excess for aluminium ions / (precipitate/solid) remains in excess for calcium ions both (ions) form a white {precipitate/solid} allow both will turn white for 1 mark allow more for excess ignore clear 3 rd mark dependent on first and/or second mark being awarded (3)

8 number 4(a) Answer An explanation that combines identification understanding (1 mark) and reasoning/justification understanding (1 mark): the flame test only confirms the presence of lithium ions/li + but another test is needed to confirm the identity of the anion/negative ion/co 3 2 OR Mark the red flame test shows the presence of calcium ions Ca 2+ and not lithium ions/li + the student did not test for carbonate ions Answer number 4(b) name: sodium sulfate formula: Na 2 SO 4 Mark Allow formula consequential on incorrect name Answer Mark number 4(c) C number 4(d)(i) number 4(d)(ii) Answer Additional guidance Mark An answer that provides a description by making reference to: test gas with moist (red) litmus paper turns blue Allow universal indicator paper/ph paper and yellow to blue/purple Answer Additional guidance Mark An answer that provides a description by making reference to: iron(ii) green/pale green/greygreen and precipitate /solid iron(iii) red-brown/brown and precipitate /solid Allow two correct colours Answer number 4(d)(iii) (Fe OH ) Fe(OH) 3 Mark

9 5(a) C 5(b) CuCl 2 ensure that 2 is subscript at most half the size of Cl and cases are correct ignore correct charges reject an overall charge 5(c) D 5(d) A description including the following 2 max if reactants and limewater are in the wrong vessels with the correct test (3) marks can be awarded for the first two marking points by labelling the diagram put/mix/react (sodium) carbonate and acid in (conical) flask reactants for sodium carbonate and acid put limewater in test tube (carbon dioxide produced) turns lime water {milky/cloudy/white precipitate}

10 5(e) A description including three of the following max 2 marks if clear error in process, e.g. heat/add acid/evaporate (3) make {solutions/dissolve}/ {mix/react} solutions precipitate (of copper carbonate) filter ignore colours of precipitate accepts forms a solid for precipitate wash (with water) leave to dry/dry in oven/dry between filter paper

11 Qualitative Analysis Test for Ions Mark Scheme 2 Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Qualitative Analysis: Test for Ions Booklet Mark Scheme 2 Time Allowed: 54 minutes Score: /45 Percentage: /100

12 1(a) C : copper sulfate and sodium chloride 1(b) copper sulfate blue-green or allow blue or green or green-blue sodium chloride yellow reject orange and yellow-orange colour mark consequential on correct metal (compound) 1(c)(i) An explanation linking weak intermolecular forces /weak forces between molecules little {heat / energy} needed to separate (molecules) bonds / attractions in place of forces intermolecular forces between {atoms / bonds} loses 1 st marking point any answer in terms of covalent or ionic bonding scores zero 1(c)(ii) A description linking use separating funnel run off lower {layer / liquid} / OWTTE alternative description of separating funnel eg funnel with a tap at the bottom suitable labelled diagram burette allow layers / liquids to separate ignore fractional distillation

13 1(d) Allow a diagram without labels for 2 marks shared pair in molecule rest of molecule consequent on first mark any symbols shown must be correct for the 2 nd mark allow any combination of dots and crosses for electrons wrong compound = zero marks

14 2(a) Answer symbol number of electrons atom ion atom ion chlorine 18 sodium Na + 11 Mark (3) 2(b)(i) NaCl + AgNO 3 NaNO 3 + AgCl Ag + + Cl - AgCl reactant formulae product formulae ignore state symbols do not give if incorrectly balanced Answer 2(b)(ii) to remove other ions that would also form a white precipitate Acceptable answers Mark

15 Indicative content QWC *2(c) An explanation linking some of the following points Mark For a sample to conduct electricity charged particles must be present they must be free to move water does not conduct because it is (simple molecular) covalent exists as molecules contains no/(very few) charged particles solid sodium chloride does not conduct because although it contains ions / cations / anions which are charged particles they are not free to move because they are held together by strong electrostatic forces/ ionic bonds in lattice sodium chloride solution conducts because ions / cations / anions are present which are charged particles they are free to move because the water has cut down the forces between the ions ions have separated move to electrode of opposite charge (6) Level 0 No rewardable content 1 1- a limited explanation e.g. water is covalent and sodium chloride is ionic the answer communicates ideas using simple language and uses limited scientific terminology spelling, puncuation and grammar are used with limited accuracy 2 3- a simple explanation e.g. water is covalent and does not conduct because there are no charged particles: sodium chloride is ionic therefore solution conducts because ions move the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, puncuation and grammar are used with some accuracy 3 5- a detailed explanation e.g. in solid sodium chloride the ions are held in a lattice by strong forces but in sodium chloride solution the ions are free to move: water is covalent so contains no charged particles the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, puncuation and grammar are used with few errors

16 3(a)(i) B lead chloride 3(a)(ii) An explanation linking two of strong (electrostatic) forces of attraction Any reference to molecules/molecular/intermolecul ar/covalent scores 0 marks strong (ionic) bonds between oppositely charged ions so requires lot of heat/energy to overcome forces/break bonds positive and negative ions reject charged atoms for this mark ignore hard to melt/high temperature needed 3(a)(iii) A description including Accept correct formulae M1 add (dilute) nitric acid M2 add silver nitrate (solution) M3 forms white ppt/solid If use any other acid can score M2 and M3 dependent on use of silver nitrate Alternative method: Electrolyse Chlorine formed Bleaches litmus/ph paper Ignore smell (3)

17 Indicative Content Mark QWC 3(b) A description including some of the following points ion formation magnesium atoms lose electrons each magnesium atom loses two electrons to acquire full outer shell magnesium (configuration) becomes 2.8 forms Mg 2+ ion electrons transferred to oxygen atoms oxygen atoms gain electrons each oxygen atom gains two electrons oxygen (configuration) becomes 2.8 to acquire full outer shell forms O 2- ion structure magnesium ions attract oxide ions due to opposite charges ions pack close together ratio of ions 1: 1 ions arranged in lattice giant (ionic) (structure) (6) diagram can be credited for any points Level 0 No rewardable content a limited description e.g. magnesium atoms lose electrons and oxygen atoms gain electrons e.g. magnesium oxide is a giant structure the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy a simple description e.g. magnesium atoms lose two electrons to form positive ions and oxygen atoms gain two electrons to form negative ions e.g. magnesium atoms lose electrons and oxygen atoms gain electrons and magnesium oxide is a giant structure the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy a detailed description e.g. each magnesium atom transfers two electrons to an oxygen atom and the opposite charged ions (Mg 2+ /O 2- ) formed attract each other to form a giant (ionic) lattice the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors

18 4(a)(i) 2- A carbonate ion CO 3 4(a)(ii) A description including maximum if additional reagents added warm / heat / boil {gas/ammonia} turns (damp red/pink) litmus blue / (damp red/pink) litmus turns blue when held above (the mixture) ignore any ppt allow pungent smell / smell of {ammonia/wet nappies} /alkaline gas / effect of ammonia on other named indicators /dense white fumes with conc hydrochloric acid ignore litmus turns blue in ammonium ions/sodium hydroxide/mixture do not allow gas/ammonia if blue litmus turns red/pink 4(b) Al OH - Al(OH) 3 allow multiples OH - Al(OH) 3 balancing 3, conditional on correct formulae allow HO - allow Al(HO) 3 do not allow Al(HO) 3 /lower case h ignore state symbols/3na + on both sides (3)

19 Indicative Content QWC *4(c) An explanation including some of the following points Mark test for cation flame test if the flame is yellow/not lilac, sodium ions are present if the flame is lilac/not yellow, potassium ions are present test for iodide ions make a solution of the crystals in water add dilute nitric acid add silver nitrate solution if there is a yellow precipitate, iodide ions are present if there is no precipitate, sulfate ions are present Ag + + I AgI OR make a solution of the crystals in water add chlorine water then cyclohexane if the cyclohexane/top layer turns purple, iodide ions were present if there is no colour change, sulfate ions are present Cl 2 + 2I - 2Cl - + I 2 test for sulfate ions make a solution of the crystals in water add dilute {hydrochloric/nitric} acid add barium {chloride/nitrate} solution if there is a white precipitate, sulfate ions are present if there is no precipitate, iodide ions are present Ba 2+ + SO 4 2- BaSO 4 (6) Level 0 No rewardable content a limited description of test for any 1 ion e.g. flame test, yellow flame, sodium ions are present. the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy a simple description to identify a cation and an anion e.g. if the substance is sodium sulfate, it will give a yellow flame in a flame test and a white precipitate with barium chloride solution. the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy a detailed description to identify at least 3 ions e.g. carry out a flame test, yellow flame, sodium ions present, lilac flame, potassium ions present, add silver nitrate solution to solution of substance, yellow precipitate, iodide ion. the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors

20 Qualitative Analysis Test for Ions Mark Scheme 3 Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Qualitative Analysis: Test for Ions Booklet Mark Scheme 3 Time Allowed: 15 minutes Score: /12 Percentage: /100

21 1(a) CaCl 2 = (=111) 0.2 scores 3 (3) THEN moles = 11.1 / 111 conc = moles x 1000/500 OR mass conc = 11.1 x 1000/500 conc = mass conc/111 (= 0.1) (=0.2) (=22.2) (= 0.2) ecf: 11.1 / Mr ecf: mass conc / 111 1(b)(i) A description linking pipette one practical point eg draw liquid up to line/ use pipette filler/ rinse first / read at eye level ignore burette etc for 1 st mpt if using measuring cylinder/ burette allow suitable practical point eg read at eye level/ add dropwise from burette near 25 cm 3 ignore as 2 nd point: transfer liquid to flask / safety precautions 1(b)(ii) D cm 3

22 QWC *1(c) Indicative Content A description / explanation including some of the following points Mark (6) soft add soap (solution) shake/ mix lather (immediately) no scum/ no precipitate permanent hard add soap (solution) shake no lather / less than with soft water scum/ precipitate boiled sample same results / boiling does not change becomes soft after ion exchange but not after boiling temporary hard add soap (solution) shake no lather / less than with soft water scum/ precipitate boiled sample after boiling precipitate / (lime)scale formed lather (immediately) credit quantitative approaches e.g. titration with soap solution

23 Level 0 No rewardable content a limited description e.g. test and one result / when shaken with soap, soft water makes lather but no scum the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy a simple description e.g. describe test and results to distinguish the soft water and the two samples that are hard water / when shaken with a small amount of soap, soft water makes a lather and no scum but the other waters make scum but no (less) lather the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy a detailed description e.g. describe test and results to identify all three of the samples / as 3-4 and boil the two hard water samples and repeat test. That which now gives a lather is temporarily hard the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors

24 Hydrocarbons Mark Scheme 1 Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Hydrocarbons Booklet Mark Scheme 1 Time Allowed: 59 minutes Score: /49 Percentage: /100

25 1(a)(i) An explanation linking (3) (a compound containing) hydrogen and carbon (hydrogen and carbon) only ignore H and C reject {ions/molecule} of carbon and hydrogen reject mixture reject oxygen contains double / multiple bond (between carbon atoms) ignore spare bonds allow carbon atoms not joined to the maximum number of other atoms 1(a)(ii) B cracking 1(a)(iii) A description to include (bromine water is) orange decolourises / turns colourless allow brown / yellow or combinations eg orange-yellow ignore red (alone) ignore clear / changes colour / discolour

26 1(b)(i) D 1(b)(ii) waterproof / rot-proof / strong / flexible / does not react with oxygen / water resistant / weather proof allow durable / tough ignore ductile / stretchy 1(b)(iii) not biodegradable / persist in landfill sites / does not decompose ignore answers in terms of burning / allow takes a long time to rot / decompose / takes up space in landfill

27 2(a) Answer Mark any 3 carbon molecule and one C=C fully correct molecule with all bonds 2(b)(i) A 333 dm 3 2(b)(ii) 2(b)(iii) An explanation linking all / three gases present/ nitrogen, hydrogen and ammonia ammonia decomposes/ ammonia turns back to reactants/ reaction goes both ways / reversible reject ammonium ignore incomplete reaction assume that both reactions refer to forward and backward reaction allow dynamic equilibrium An explanation linking increased / higher {yield / amount of ammonia} mark independently ignore high yield because fewer (gas) molecules/ moles on RHS/ 4 mole(cule)s on left and 2 on right/ decreased volume on RHS/equilibrium shifts to RHS/ equilibrium shifts in forward direction reject answers referring to exothermic or endothermic ignore any references to rate

28 2(b)(iv) An explanation to include mark independently (3) rate increased/ time to reach equilibrium reduced because gas molecules closer / more concentrated so increased collision rate / more collisions in a given time / more frequent collisions ignore any refs to equilibrium ignore time is faster / allow quicker allow atoms/ particles instead of molecules; allow more molecules present (in same container) do not allow more collisions

29 3(a)(i) A explanation linking the following contains carbon (atoms) and hydrogen (atoms) reject carbon molecules and hydrogen molecules only all single bonds/no double bonds ignore no spare bonds (3) 3(a)(ii) remains orange 3(b)(i) cracking 3(b)(ii) any two reasons from insufficient petrol / supply (from crude oil) not enough petrol higher demand for petrol more fuel oil fraction than needed too much fuel oil petrol is more useful than fuel oil 3(c) CH 4 + 2O 2 CO 2 + 2H 2 O (3) correct multiples ignore state symbols LHS RHS balancing correct formula (3)

30 4(a) ( the liquid oil is changed into a solid 4(b)(i) B sodium hydroxide 4(b)(ii) An explanation linking any two of tail / {hydrophobic / hydrocarbon } end into grease head / {anion / hydrophilic} end into water allows grease to mix with water when surrounded by soap (anions) / grease is surrounded by soap surface tension lowered allow correctly labelled diagram head is soluble in water 4(c)(i) propanoic (acid) 4(c)(ii) 4(d) CH 3 COOH + C 2 H 5 OH CH 3 COOC 2 H 5 + H 2 O award one mark if incorrectly balanced correct products but no / incorrect reactants shown allow correct molecular formulae allow correct multiples ignore state symbols (making) fibres/fleece/clothing/ fabrics/bedding/computer mouse mats/yarns/ropes/safety belts/filters/insulating tape/wood finishes/(plastic) carrier bags allow any named item of clothing

31 5(a) C CH3CH3 5(b) carbon skeleton correct including double bond rest of molecule correct allow CH 3 5(c) CH 4 + 2O 2 CO 2 + 2H 2 O reactant formulae product formulae balancing of correct formulae accept multiples reject incorrect use of cases and non-subscripts (3)

32 Indicative content QWC *5(d) advantages renewable / sustainable more plants can be grown crops use up carbon dioxide and produce oxygen when growing /photosynthesising carbon neutral because the carbon produced during combustion is used when growing the plants does not use up crude oil/non-renewable resources Mark (6) disadvantages crops grown for bio-fuels use up land land could otherwise be used to provide homes / less farmland available for growing food crops lots of crops required to provide a small amount of bio-methane bad season reduces availability carbon emissions due to transport and production if qualified Leve 0 No rewardable content l 1 1- a limited description e.g. using bio-methane conserves fossil fuels and uses up carbon dioxide when plants are grown the answer communicates ideas using simple language and uses limited scientific terminology spelling, puncuation and grammar are used with limited accuracy 2 3- a simple description e.g. growing plants to produce biomethane is sustainable and conserves fossil fuels but uses up lots of farm land which could be used to grow plants for food the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, puncuation and grammar are used with some accuracy detailed description e.g growing plants remove carbon dioxide from the air during photosynthesis and conserves fossil fuels but lots of crops are required to make biomethane and this uses up farm land which could otherwise be used to grow crops for food the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, puncuation and grammar are used with few errors

33 Hydrocarbons Mark Scheme 2 Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Hydrocarbons Booklet Mark Scheme 2 Time Allowed: 60 minutes Score: /50 Percentage: /100

34 1(a)(i) D C 4 H 10 1(a)(ii) allow -CH 3 one C=C in a molecule with three consecutive carbon atoms rest of structure correct, ignore bond angles, conditional on first marking point do not allow two C=C in a molecule allow for completely correct dot and cross diagram 1(b) C oxidised 1(c)(i) A description including two from effervescence / fizzing / bubbles of gas ignore {cloudy/white ppt} / gas formed /colour change /name of gas / changes to a liquid solid {disappears/clears} /(colourless)solution formed (solid/sodium carbonate/it) dissolves 1(c)(ii) CH 3 COOC 2 H 5 /CH 3 COOCH 2 CH 3 / CH 3 CO 2 C 2 H 5 / CH 3 CO 2 CH 2 CH 3 / C 2 H 5 O 2 CCH 3 / CH 3 CH 2 OOCCH 3 allow displayed formulae/ C 4 H 8 O 2 do not allow formulae ending in COOH/-COO or any formula that does not show an ester H 2 O do not allow H2O / H 2 O /lower case h/hoh maximum if additional incorrect balancing ignore state symbols

35 2(a)(i) LPG, petrol and diesel 2(a)(ii) An explanation linking two of the following points use of {fractions / large molecules / long chain hydrocarbons} of {less demand / less useful / lower value} / ORA to meet demand / small molecules needed reject useless use up excess kerosene / fuel oil and bitumen to make more petrol / LPG / alkenes 2(b) B the boiling point of the hydrocarbon increases 2(c)(i) C 2 H 4 2(c)(ii) n ignore n missing on polymer structure LHS RHS n C 2 H 4 (C 2 H 4 ) n Note: Displayed formulae alkene with C=C polymer single bonds between atoms with continuation bonds Allow: n (where X could be CH 3 or similar) Allow any number of C 2 H 4 on LHS drawn out with corresponding structure of polymer on RHS

36 2(d)(i) An explanation linking the following points greenhouse gas / traps heat in atmosphere traps infra-red radiation / increases greenhouse effect reject reference to UV may lead to increasing global temperature / global warming melting {ice caps / glaciers} / climate change / sea-level rising / loss of habitats reject reference to ozone layer 2(d)(ii) An explanation linking two of the following points sulfur dioxide formed (during combustion of fuel) SO 2 sulfur dioxide {dissolves in rain / forms acid (rain)} an effect of acid rain e.g. harms {fish / plants / statues / buildings} / lowers ph of lakes possible harm to human respiration

37 number 3(a) Answer C Mark number Answer Additional guidance Mark 3(b) molecular formula C 5 H 10 structure number 3(c)(i) Answer Additional guidance Mark calculates relative molecular mass of C 4 H 9 OH calculates mass of C 4 H 9 OH produced final answer = 1.9 (kg) Example of calculation Relative molecular mass of C 4 H 9 OH = (4 12) + (9 1) = 74 number 3(c)(ii) Answer A Mass of C 4 H 9 OH produced = (74 56) 1.4 Accept 1.85 (kg) Award full marks for use of moles/correct numerical answer without working (3) Mark number Answer Mark 3(d) X and Y are both unsaturated/contain {multiple/double} bonds/alkenes Z is saturated/contains no {multiple/double} bonds/alkane

38 4(a) C 4(b) correct repeating unit any answer with double bonds = 0 two correct units shown with continuation bonds Allow if correct and more than two units shown 4(c) A description including two of the following points bromine (water) (bromine water) turns (from orange) to colourless/or is decolourised Ignore clear/discoloured 4(d)(i) 17 (g) seventeen (g) 4(d)(ii) An explanation linking two of the following break down of hydrocarbons / large molecules / alkanes into small(er) molecules Reject chains of molecules /polymers Ignore chains into alkanes and alkenes

39 4(d)(iii) An explanation linking two of the following: less demand for (fractions containing) large molecules ORA large molecules are less useful ORA Reject are useless specific use of product fractions e.g. petrol / fuel for cars to make alkenes named alkenes specific use of alkenes produced e.g. as monomers / to make polymers / to make plastics

40 5(a)(i) allow methyl group written as CH 3 one C=C in a three consecutive carbon atom molecule rest of structure correct, ignore bond angles, conditional on first marking point 5(a)(ii) C 7 H 16 5(b) A description including (3) add bromine (water) / aqueous bromine (and shake the tube) stays orange / no change / does not go colourless in {propane/alkane} turns colourless / decolorises in {propene/alkene} Maximum 1 mark for 2 correct observations with an incorrect reagent or no reagent specified Allow recognisable spelling for bromine Allow yellow / brown or combinations of these for orange Ignore just red Ignore clear / discoloured one correct test with statement or clear implication that the other must be the other gas for full marks eg add bromine water to both gases, the one that turns it colourless is propene, scores 3 marks as it is clearly implied that the other gas does not turn it colourless

41 Indicative Content QWC *5(c) An explanation including some of the following points Making the polymer many propene molecules join/react together form a long chain polymerisation reaction propene is the monomer propene is unsaturated / has a double bond poly(propene) has single bonds propene is a gas and forms poly(propene) which is a solid the C=C bond breaks / opens up Mark Properties of poly(propene) with related uses e. property flexible, low density (lightweight), shatterproof, high softening point, non-toxic, strong, tough, good insulator, water proof, resistant to corrosion, long lasting, can be moulded into shape, can be made into fibres Uses of poly(propene) use to make plastic bags, packaging, buckets, bowls, food containers, ropes, carpets, thermal underwear, Thinsulate items, toys, bottles, bottle caps, laboratory equipment, medical equipment, pipes, car bumpers, crates, furniture, tubing (6) Level 0 No rewardable content a limited explanation of how to make the polymer or properties or uses e.g. propene molecules join together to form the polymer / polypropene can be used to make carpets the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy a simple explanation of how to make the polymer and/or properties and/or uses e.g. propene molecules are monomers and join together to make poly(propene)/ poly(propene) is used to make buckets because it can be moulded into shape the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy a detailed explanation including reference to how to make the polymer, its uses and properties e.g. propene molecules have a double bond and poly(propene) can be used to make washing up bowls because it is strong. / propene molecules have a double bond and many of them join together to make polypropene which is used to make ropes. the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors

42 Hydrocarbons Mark Scheme 3 Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Hydrocarbons Booklet Mark Scheme 3 Time Allowed: 30 minutes Score: /25 Percentage: /100

43 1(a) remove delivery tube from water before stopping heating other words which make sequence clear use of (Bunsen) valve 1(b) B C 4 H 8 1(c) contains a {double/multiple} bond ignore spare bonds ignore reference to number of hydrogen atoms attached. 1(d) A description to include (3) bromine water is orange red / yellow / brown any combination of these propane: (remains) orange / no colour change propene: becomes colourless /decolourises ignore clear /discolours

44 1(e) An explanation linking any two of shorter chain molecules are more useful ORA demand for shorter chain molecules ORA reject long chain molecules are useless named fraction/use/fuel meets demand reduces the excess of longer chain molecules named fraction /use/fuel (cracking) produces alkenes alkenes used to make polymers

45 number 2(a) number 2(b)(i) number 2(b)(ii) Answer C Answer (oil well) C Answer (oil well) A Mark Mark Mark number 2(c)(i) Answer Additional guidance Mark An explanation that combines identification application of knowledge (1 mark) and reasoning/justification application of understanding (2 marks): when the decane is heated it vaporises/turns to a gas decane vapour/gas breaks down as it comes in contact with hot porous pot large molecules of decane produce smaller molecules, including ethene Do not allow this point if ethane passes over hot porous pot (3) number 2(c)(ii) number 2(c)(iii) Answer B Answer 2C 10 H O 2 20CO H 2 O Mark Mark LHS RHS both numbers correct

46 3(a) C 3(b)(i) An explanation linking two of the following points break down of (hydrocarbons/molecules / alkanes) Ignore chains of.. / polymers Ignore separating Ignore reasons for cracking into smaller (hydrocarbons/molecules / alkanes) 3(b) (ii) an explanation linking the following (molecule) containing (carbon-carbon) double / multiple bond Allow references to addition reactions. Ignore alkene, spare bonds, doesn t have max no of atoms or H bonded contains (atoms of) carbon and hydrogen only Can only score third point if second point scored (3) 3(b)(iii) a description including the following from orange/brown/yellow Allow red-brown but no other mention of red to colourless Ignore clear / discolour

47 Polymers Mark Scheme Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Polymers Booklet Mark Scheme Time Allowed: 62 minutes Score: /51 Percentage: /100

48 number Answer Mark 1(a) An explanation that combines identification improvement of the experimental procedure (1 mark) and justification/reasoning which must be linked to the improvement (1 mark): reverse the boiling tubes/pass gas through the tube in ice water first so that if any liquid condenses in the tube it must have come from the burning wax (and not from the limewater)

49 number *1(b) Indicative content Answers will be credited according to candidate's deployment of knowledge and understanding of the material in relation to the qualities and skills outlined in the generic mark scheme. The indicative content below is not prescriptive and candidates are not required to include all the material which is indicated as relevant. Additional content included in the response must be scientific and relevant. Candidates choose appropriate monomers to illustrate the formation of different polymers. Mark polymer molecules are long chains made up of simple repeating units use chloroethene (only) to form poly(chloroethene) which is addition polymerisation use ethane-1,2-diol and ethanedioic acid to form a polyester which is condensation polymerisation one of the bonds in the double bond in chloroethene molecule breaks and chloroethene molecules join together to form a long chain molecule equation identification of repeat unit alcohol group combines with a carboxylic acid group and an ester (link) formed with a water (molecule) eliminated equation ester link shown identification of repeat unit (6)

50 Level Mark Descriptor 0 No awardable content. Level The explanation attempts to link and apply knowledge and understanding of scientific ideas, flawed or simplistic connections made between elements in the context of the question. (AO2) Lines of reasoning are unsupported or unclear. (AO2) Level The explanation is mostly supported through linkage and application of knowledge and understanding of scientific ideas, some logical connections made between elements in the context of the question. (AO2) Lines of reasoning mostly supported through the application of relevant evidence. (AO2) Level The explanation is supported throughout by linkage and application of knowledge and understanding of scientific ideas, logical connections made between elements in the context of the question. (AO2) Lines of reasoning are supported by sustained application of relevant evidence. (AO2) number 1(c)(i) Answer carboxylic acids Marks number 1(c)(ii) Answer Marks

51 2(a) C alkenes are unsaturated hydrocarbons 2(b) poly(ethene) polythene/polyethylene H H C H C CH 3 n continuation bonds need not go through brackets Allow bond pointing to any part of CH 3 2(c) An explanation linking two of non biodegradable persist in landfill sites OR produce gases/fumes when burnt M1 gases may be toxic/harmful M2 OR cannot be recycled new {raw material/crude oil} needed {do not/take (very) long time to} decompose/rot/disintegrate/degr ade stays for long time take up a lot of space (in landfill sites) a named gas linked to the environmental problem it causes e.g. carbon dioxide is a greenhouse gas Ignore pollutants (need to use) finite resources

52 Indicative Content QWC *2(d) An explanation including some of the following points A good fuel should Burning considerations ignite easily Mark burn easily release a lot of /sufficient heat energy when it is burnt Usage considerations be safe to use be safe/easy to transport be {safe/easy/convenient} to store (6) be reasonably cheap Supply considerations readily available/good supply be renewable/sustainable/not finite Products considerations not produce (much) solid/ash when burnt not produce much/any smoke contain little/no sulfur not produce {toxic/harmful} gases/fumes carbon neutral not produce too much carbon dioxide or other named gas such as sulfur dioxide or greenhouse gases Level 0 No rewardable content a limited description covering two aspects: e.g. burn easily and safe to use OR one aspect covered in more detail e.g. is cheap and easy to transport the answer communicates ideas using simple language and uses limited scientific terminology, spelling, punctuation and grammar are used with limited accuracy

53 3(a)(i) An explanation linking (3) (a compound containing) hydrogen and carbon (hydrogen and carbon) only ignore H and C reject {ions/molecule} of carbon and hydrogen reject mixture reject oxygen contains double / multiple bond (between carbon atoms) ignore spare bonds allow carbon atoms not joined to the maximum number of other atoms 3(a)(ii) B cracking 3(a)(iii) A description to include (bromine water is) orange decolourises / turns colourless allow brown / yellow or combinations eg orange-yellow ignore red (alone) ignore clear / changes colour / discolour

54 3(b)(i) D 3(b)(ii) waterproof / rot-proof / strong / flexible / does not react with oxygen / water resistant / weather proof allow durable / tough ignore ductile / stretchy 3(b)(iii) not biodegradable / persist in landfill sites / does not decompose ignore answers in terms of burning / allow takes a long time to rot / decompose / takes up space in landfill

55 4(a) ( the liquid oil is changed into a solid 4(b)(i) B sodium hydroxide 4(b)(ii) An explanation linking any two of tail / {hydrophobic / hydrocarbon } end into grease head / {anion / hydrophilic} end into water allows grease to mix with water when surrounded by soap (anions) / grease is surrounded by soap surface tension lowered allow correctly labelled diagram head is soluble in water 4(c)(i) propanoic (acid) 4(c)(ii) 4(d) CH 3 COOH + C 2 H 5 OH CH 3 COOC 2 H 5 + H 2 O award one mark if incorrectly balanced correct products but no / incorrect reactants shown allow correct molecular formulae allow correct multiples ignore state symbols (making) fibres/fleece/clothing/ fabrics/bedding/computer mouse mats/yarns/ropes/safety belts/filters/insulating tape/wood finishes/(plastic) carrier bags allow any named item of clothing

56 5(a)(i) allow methyl group written as CH 3 one C=C in a three consecutive carbon atom molecule rest of structure correct, ignore bond angles, conditional on first marking point 5(a)(ii) C 7 H 16 5(b) A description including (3) add bromine (water) / aqueous bromine (and shake the tube) stays orange / no change / does not go colourless in {propane/alkane} turns colourless / decolorises in {propene/alkene} Maximum 1 mark for 2 correct observations with an incorrect reagent or no reagent specified Allow recognisable spelling for bromine Allow yellow / brown or combinations of these for orange Ignore just red Ignore clear / discoloured one correct test with statement or clear implication that the other must be the other gas for full marks eg add bromine water to both gases, the one that turns it colourless is propene, scores 3 marks as it is clearly implied that the other gas does not turn it colourless

57 Indicative Content QWC *5(c) An explanation including some of the following points Making the polymer many propene molecules join/react together form a long chain polymerisation reaction propene is the monomer propene is unsaturated / has a double bond poly(propene) has single bonds propene is a gas and forms poly(propene) which is a solid the C=C bond breaks / opens up Mark Properties of poly(propene) with related uses e. property flexible, low density (lightweight), shatterproof, high softening point, non-toxic, strong, tough, good insulator, water proof, resistant to corrosion, long lasting, can be moulded into shape, can be made into fibres Uses of poly(propene) use to make plastic bags, packaging, buckets, bowls, food containers, ropes, carpets, thermal underwear, Thinsulate items, toys, bottles, bottle caps, laboratory equipment, medical equipment, pipes, car bumpers, crates, furniture, tubing (6) Level 0 No rewardable content a limited explanation of how to make the polymer or properties or uses e.g. propene molecules join together to form the polymer / polypropene can be used to make carpets the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy a simple explanation of how to make the polymer and/or properties and/or uses e.g. propene molecules are monomers and join together to make poly(propene)/ poly(propene) is used to make buckets because it can be moulded into shape the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy a detailed explanation including reference to how to make the polymer, its uses and properties e.g. propene molecules have a double bond and poly(propene) can be used to make washing up bowls because it is strong. / propene molecules have a double bond and many of them join together to make polypropene which is used to make ropes. the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors

58 Alcohols & Carboxylic Acids Mark Scheme 1 Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Alcohols & Carboxylic Acids Booklet Mark Scheme 1 Time Allowed: 53 minutes Score: /44 Percentage: /100

59 1(a)(i) C 4H 8O 2 capital letters; numbers must be subscripts ignore structural formulae such as CH 3COOCH 2CH 3 i.e. must have just C 4, H 8 and O 2 in any order. Answer 1(a)(ii) ethanol + ethanoic acid ethyl ethanoate + water LHS= 1 mark [allow acetic acid]; RHS= 1 mark [allow ethyl acetate] Allow = for arrow. Fully correct formula equation = 2 (part mark not possible with formulae) Mark 1(a)(iii) 1(b)(i) no vapour/ little vapour (given off) / it is not a gas / it is a solid (not vapour) OR small amount/ concentration in sweets allow gas for vapour allow ethyl ethanoate is in a liquid state D soap 1(b)(ii) A description linking filter / decant off water (then) wash/rinse Can only score second mark if first marking point awarded ignore anything before filtering that would not contaminate soap but do not allow to evaporate water/ heat BEFORE filtering ignore anything after washing, including drying Answer Mark 1(c) C unsaturated molecules in the liquid oil become saturated

60 2(a)(i) A description including two of the following dissolve the sugar/aqueous solution warm/ C in absence of air / no oxygen/ anaerobic / attach airlock ph neutral / slightly acidic /4-7 sterile conditions ignore any mention of pressure ignore incorrect answers ignore heat / hot allow any temperature or range within allowed ignore clean etc ignore optimum {temp/pressure/ph} 2(a)(ii) B fractional distillation 2(a)(iii) C 6H 12O 6 2 C 2H 5OH + 2 CO 2 allow C 2H 6O/ CH 3CH 2OH for C 2H 5OH reject CO2 / CO 2 correct formulae (with no others) balancing the three formulae ignore state symbols allow multiples 2(b)(i) Any two of (reacts with) steam catalyst/phosphoric acid high temperature / 200 C C high pressure/ atm allow reacts with water ignore incorrect catalyst ignore hot / heat

61 2(b)(ii) An explanation linking any three of LAND: country needs land for: farming / food / crops / homes /not enough land to grow sugar crop for fermentation ignore incorrect responses ignore land needed for growing yeast (3) OIL SUPPLY: (reliable supply of) crude oil for ethene SPEED: fermentation slow/batch; hydration continuous/ fast PURITY: hydration makes {pure(r) ethanol / high concentration} ignore cheaper/ easier ignore yield ATOM ECONOMY: higher atom economy for ethene process

62 3(a) ( add yeast, temperature of 35 o C 3(b) C 2 H 4 + H 2 O C 2 H 5 OH award one mark max if incorrectly balanced allow correct molecular formula C 2 H 6 O allow H 4 C 2 correct multiples ignore state symbols 3(c)(i) A description linking any two from same general formula same functional group (consecutive) compounds differ by CH 2 gradual variation in physical properties allow C n H 2n+1 OH allow C n H 2n or any correct general formula ignore same properties/physical properties {similar / same} chemical {properties / reactions} allow a correct trend, e.g. bp increases with number of carbon atoms 3(c)(ii) allow OH allow correct dot and cross diagram 3(d)(i) oxidation

63 3(d)(ii) A description including any two from effervescence/fizzing/bubbling ignore incorrectly named gases ignore gas given off/evolved allow magnesium floats on surface of acid solid disappears colourless solution allow solid dissolves ignore solution turns colourless ignore clear

64 4(a) Answer C 2 H 4 + H 2 O C2H 5 OH C 2 H 4 as reactant Acceptable answers do not allow H2O / H 2 O /lower case h/hoh Mark rest of equation correct conditional on C 2 H 4 as a reactant allow C 2 H6O for ethanol ignore state symbols 4(b) Answer A description including any two from dissolve sugar in water / sugar solution Acceptable answers allow glucose solution ignore carbohydrate Mark ( add) yeast warm / any temperature or range within 15 to 40 o C allow room temperature ignore heat unless specified temperature ignore optimum temperature anaerobic / {no/little} { air/oxygen} c enter the apparatus ( 1) do not allow just sealed container ignore fractional distillation

65 4(c) An explanation linking Marking point 1 sugar- one from sugar obtained from {plants /crops/specific crop} (plenty of) land available to grow {plants /crops/specific crop} (for fermentation) Marking point 2 - ethene ethene obtained from {crude oil / fractional distillation /cracking} ignore answers that just repeat the information in the question ignore vague answers such as carbon neutral/environmentally friendly for marking point 1 OR 2, allow plants renewable/{crude oil/ethene} non-renewable Marking point 3 cost/energy one from cannot afford to buy crude oil crude oil is too expensive more expensive to {use/buy/produce} ethene cheaper to use fermentation allow {little/no} {heat/energy} required for fermentation allow {high temperature /high pressure} required for hydration of ethene (3) 4(d) An explanation including any two from formulae differ by CH 2 general formula is C n H 2n+1 OH same general formula all have {OH/hydroxyl group} allow increase by {CH 2 /1 carbon and 2 hydrogens} do not allow incorrect general formula allow have similar chemical {reactions /properties}/same functional group/oh from an incorrect general formula ignore hydroxide /all end in (an)ol /all alcohols ignore physical properties maximum if hydroxide ions /carboxyl group

66 5(a)(i) D C 4 H 10 5(a)(ii) allow -CH 3 one C=C in a molecule with three consecutive carbon atoms rest of structure correct, ignore bond angles, conditional on first marking point do not allow two C=C in a molecule allow for completely correct dot and cross diagram 5(b) C oxidised 5(c)(i) A description including two from effervescence / fizzing / bubbles of gas ignore {cloudy/white ppt} / gas formed /colour change /name of gas / changes to a liquid solid {disappears/clears} /(colourless)solution formed (solid/sodium carbonate/it) dissolves 5(c)(ii) CH 3 COOC 2 H 5 /CH 3 COOCH 2 CH 3 / CH 3 CO 2 C 2 H 5 / CH 3 CO 2 CH 2 CH 3 / C 2 H 5 O 2 CCH 3 / CH 3 CH 2 OOCCH 3 allow displayed formulae/ C 4 H 8 O 2 do not allow formulae ending in COOH/-COO or any formula that does not show an ester H 2 O do not allow H2O / H 2 O /lower case h/hoh maximum if additional incorrect balancing ignore state symbols

67 Alcohols & Carboxylic Acids Mark Scheme 2 Level Edexcel Subject Chemistry Exam Board GCSE(9-1) Topic Separate Chemistry 2 Sub Topic Alcohols & Carboxylic Acids Booklet Mark Scheme 2 Time Allowed: 14 minutes Score: /11 Percentage: /100

68 number Answer Mark 1(a) An explanation that combines identification improvement of the experimental procedure (1 mark) and justification/reasoning which must be linked to the improvement (1 mark): reverse the boiling tubes/pass gas through the tube in ice water first so that if any liquid condenses in the tube it must have come from the burning wax (and not from the limewater)

69 number *1(b) Indicative content Answers will be credited according to candidate's deployment of knowledge and understanding of the material in relation to the qualities and skills outlined in the generic mark scheme. The indicative content below is not prescriptive and candidates are not required to include all the material which is indicated as relevant. Additional content included in the response must be scientific and relevant. Candidates choose appropriate monomers to illustrate the formation of different polymers. Mark polymer molecules are long chains made up of simple repeating units use chloroethene (only) to form poly(chloroethene) which is addition polymerisation use ethane-1,2-diol and ethanedioic acid to form a polyester which is condensation polymerisation one of the bonds in the double bond in chloroethene molecule breaks and chloroethene molecules join together to form a long chain molecule equation identification of repeat unit alcohol group combines with a carboxylic acid group and an ester (link) formed with a water (molecule) eliminated equation ester link shown identification of repeat unit (6)

70 Level Mark Descriptor 0 No awardable content. Level The explanation attempts to link and apply knowledge and understanding of scientific ideas, flawed or simplistic connections made between elements in the context of the question. (AO2) Lines of reasoning are unsupported or unclear. (AO2) Level The explanation is mostly supported through linkage and application of knowledge and understanding of scientific ideas, some logical connections made between elements in the context of the question. (AO2) Lines of reasoning mostly supported through the application of relevant evidence. (AO2) Level The explanation is supported throughout by linkage and application of knowledge and understanding of scientific ideas, logical connections made between elements in the context of the question. (AO2) Lines of reasoning are supported by sustained application of relevant evidence. (AO2) number 1(c)(i) Answer carboxylic acids Marks number 1(c)(ii) Answer Marks