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Page 1 M1. (a) oxygen / O2 (do not allow air) for 1 mark 1 (b) (i) idea that it is a catalyst / it increases the rate of reaction / lowers activation energy for 1 mark 1 (ii) the reaction is exothermic or releases energy / heat for 1 mark 1 (c) idea that • hot gases from the first reaction vessel need to be cooled • incoming gases / ammonia / oxygen need to be heated • there is an energy saving / cost saving any two for 1 mark each 2 (d) water and oxygen (need both) (accept H2O and O2) for 1 mark 1 (e) idea that • breaking bonds / breaking up molecules requires a lot of energy / reaction has a high activation energy • gives a better / faster rate of reaction • the reaction is endothermic / more energy needed to break existing bonds than to form new ones allow a higher temperature gives a greater yield / pushes the equilibrium position to the right any two for 1 mark each 2 Page 2 (f) ammonia (solution) / ammonium hydroxide (credit NH3 NH4OH) nitric acid / HNO3 in any order for 1 mark each 2 [10] M2. (a) • idea that copper has free electrons / electrons that move throughout the structure gains 1 mark but • in copper, electrons from the highest (occupied) energy level /outer shell, are free / can move throughout the structure gains 2 marks 2 (b) idea that • in graphite, only three bonds are formed by each carbon atom for 1 mark • one outer electron (per atom), free to move for 1 mark • an electric current is a flow of (free) electrons* for 1 mark (* this mark to be given in either (a) or (b) but not in both) 3 [5] M3. (a) (i) idea that • two hydrogen atoms share one pair of electrons • linked by a covalent bond Page 3 • each then has two outer electrons / a full outer shell / two • electrons in the highest (occupied) energy level (2 marks may be awarded for a correct electron diagram i.e. with electrons on boundary of or within marked area). any two for 1 mark each 2 (ii) idea that • helium atoms do not give / take / share electrons / react • because the (outer) shell / orbit is full or • highest (occupied) energy level is full (but not just “contains two electrons”) for 1 mark each 2 (b) idea that • the (attractive) forces between molecules are weak (not bonds between atoms) • so little energy is required / it is easy for molecules to escape from the liquid* / escape from other molecules* (allow evaporate / change into a gas) for 1 mark each 2 [6] M4. (a) 2Cl– – 2e– → Cl2 (allow unaltered LHS to produce ½ Cl2) + Na + e– → Na (allow × 2 for all terms) (credit candidates who point out that hydrogen / H2 is in fact produced) for 1 mark each 2 Page 4 (b) for product 1*, idea of a solid / precipitate or silver bromide gains 1 mark but solid / a precipitate of silver bromide gains 2 marks for product 2*, idea of aqueous / a solution / dissolved (in water) / or sodium nitrate gains 1 mark (do not allow liquid) but aqueous / a solution / dissolved (in water) of sodium nitrate (*do not credit formulae) gains 2 marks 4 [6] M5. (a) Mg S O4 24 + 32 + 16 (×4) or 64 / evidence of all Ar’s gains 1 mark but (Mr) = 120 gains 2 marks 2 (b) evidence that 24(g) magnesium would produce 120(g) mapesiurn sulphate gains 1 mark or correct scaling by 1/6 but 20(g) magnesium sulphate gains 2 marks [credit error carried forward from (a) with full marks in (b)] 2 [4] M6. (a) 2 Na + Cl2 → 2 NaCl allow 2 Na+ Cl– for 1 mark (allow Na + ½Cl2 → Na Cl) 1 Page 5 (b) (i) idea that • it has strong (attractive) forces/bonds between ions / charged particles for 1 mark (not ‘..it has a rigid structure’- this defines a solid or ‘...particles close together’ – they are in a liquid) 1 (ii) ideas that • there is increased vibration of ions / particles on heating • ions have sufficient energy to overcome attractive forces / to break out of the • rigid structure / to move about (must be in terms of increased energy of particles lions) each for 1 mark 2 (iii) • ions can go to electrodes / ions are free to move for 1 mark [do not credit ‘ions carry charges’] 1 (c) ideas that • it has stronger attractive forces between atoms/particles (not ‘ions’) • each carbon atom forms covalent bonds with neighbouring atoms each for 1 mark 2 [7] ## (a) idea that some of the outer electrons of the atoms are free to move can move anywhere across the (giant) structure the flow of electricity is a stream of electrons Page 6 each for 1 mark or electrons carry a (negative electrical) charge 3 (b) metal element [shiny] appearance [high] melting point forms an oxide that reacts with acids to make a salt 1 of these for 1 mark non metal element forms an oxide that reacts with alkalis with chlorine forms a molecular chloride 1 of these for 1 mark semi-conductor suggests in between this, or any other for 1further mark [NB Maximum of 2 for arguing metal/non-metal only] Under each head 1 wrong reason → maximum of 1 available 2 wrong reasons → no mark available] 3 [6] M8. (a) (i) 2 H2 + O2 → 2 H2O (allow H2 + ½O2 → H2O) both circled for 1 mark 1 (ii) 4 A1 + 3 O2 → 2 A12O3 all circled for 1 mark 1 (b) idea that: must end up with the same number of atoms otherwise matter is shown to be lost/gained doesn’t show correct amount of each element/compared each for 1 mark 2 Page 7 (c) idea that: oxygen has 2 electrons short in outer shell ) in words or chlorine has 1 electron short in outer shell ) indicated on diagram (shared pair/covalent bond with) hydrogen atom supplies one further electron* *(but do not allow hydrogen gives away electron or ionic bond) for 1 mark each 3 [7] M9. (a) reference to hydrogen (atoms) ) nitrogen (atoms) ) each for 1 mark but not molecules ratio of 1N to 3H atoms for 1 further mark or 1 nitrogen atom and 3 hydrogen atoms (ignore any incorrect statements about nature of bonding) 3 (b) evidence of H=1 N = 14 O = 16 gains 1 mark but H=1 N = 14 O = 16 × 3 or 48 gains 2 marks but 63 gains 3 marks 3 [6] M10. (a) correct representation of 1 atom of hydrogen e.g. Page 8 gains 1 mark but correct representation of 1 molecule of hydrogen e.g. or H-H gains 2 marks 2 (b) idea that: hydrogen/metals form positive ions/lose electrons gains 1 mark but hydrogen and the metals form positive ions/lose electrons gains 2 marks hydrogen/non-metals form covalent bonds/share electrons gains 1 mark but hydrogen and the non-metals form covalent bonds/share electrons gains 2 marks 4 [6] M11. (i) carbon dioxide (allow CO2) for 1 mark 1 (ii) sodium nitrate (accept correct formula) for 1 mark 1 [2] ## Page 9 (a) Idea that the electrons do not belong to specific atoms/delocalised electrons [credit if done on appropriate diagram] metal atoms form positive ions the attraction which exists between particles with opposite charges, holds the metal together no specific bonds exist between adjacent atoms/ions atoms/ions can slide over each other so allowing metals to bend each for 1 mark 5 (b) some electrons in the structure are delocalised/free to move for 1 mark these free electrons carry the electric current for 1 mark from left to right across the period, atoms of elements have more free electrons gains 1 mark but from left to right across the period, atoms of elements have more free electrons because they have more electrons in the outer shells gains 2 marks 4 [9] ## (a) covalent bonds for 1 mark 1 (b) any reference to shared electrons gains 1 mark but idea that bond is shared pair of electrons gains 2 marks 2 [3] Page 10 M14. (a) any one from (as a) catalyst or to mix with promoters to speed up the reaction (process) or process is quicker do not credit just it is quicker to save energy to reduce costs or process is cheaper do not credit just it is cheaper larger surface area (than lumps of iron) or larger surface area for the (catalysed) reaction (to take place) 1 (b) (i) water or steam and methane or natural gas or North Sea gas both required either order 1 (ii) EITHER more (chance) of them colliding / coming into contact do not credit just faster OR volume of the product / ammonia less than / only half the volume of the reactants / the nitrogen and hydrogen 1 (iii) EITHER 680 (tonnes) OR 28 (of nitrogen) → 34 (of ammonia) accept any correct 14 : 17 ratio 1 560 (of nitrogen) → 34 × 20 (of ammonia) 3 [6] Page 11 M15. (i) hydrogen, hydroxide and sulphate all three and no others any order do not credit any formula(e) 1 (ii) the anode is positive 1 (so) only the negative ions are attracted to it or (so) only the hydroxide ions and the sulphate ions are attracted (to it) or (so) only the anions are attracted (to it) 1 (iii) 2H2O + O2 + 4e– 1 [4] M16. (a) (i) sodium........ positive or + both required 1 chloride... negative or – both required do not credit chlorine 1 (ii) ions not free (to move) in solid crystal / lattice ions are free to move when sodium chloride is molten 1 or ions are mobile do not credit when ions are molten allow 'particles' for ions (1) mark do not credit electrons etc 1 (iii) dissolved in water or in aqueous solution accept in solution accept in water or when a gas/ vapour or solid it will not Page 12 1 (b) (i) 40 1 (ii) (total) number of protons and neutrons (in the nucleus) 1 (c) (i) 2Ca + O2 -+ 2CaO accept any 2n : n : 2n ratio do not credit if any other change has been made 1 (ii) any two from electron(s) is / are lost from the outer shell / orbit / ring or from the shell furthest the nucleus or from the 4th shell two / both (electrons are lost) accept two electrons are lost for (2)marks accept both electrons are lost from the atom for (1) mark 2 [10] M17. (a) CaCO3 + 2HC1 → CaC12 + CO2 + H2O one mark for CO2 and H2O or H2CO3 one mark for balancing the equation 2 (b) (i) linear suitable scale for y axis ± one small square 1 accurate plots deduct one mark for each error plot 1 smooth curve through the points or a line of best fit this mark requires a neat smooth curve 1 Page 13 (ii) curve becomes almost horizontal at or above 268.5 do not credit a straight line reaching 268.5 at 11 mins accept a plot at 268.6 1 (iii) steeper initial part to curve 1 becoming nearly horizontal between 268.6 and 268.4 g 1 [8] M18. (a) Mg + 2H+ → Mg2+ + H2 * reactants correct in every detail * products correct in every detail if the spectator ions are sown then (1) mark should be credited but only if they are shown correctly on both sides e.g. Mg + 2H+ + 2CI- → Mg2+ + 2CI- + H2 2 (b) 24 (parts) of magnesium → 2 (parts) 1 of hydrogen or equally clear working (so) 6 grams/g (are needed) 1 unit required (c) (i) two (and no more) atoms shown to be sharing their single electrons examples do not credit if anything which contradicts the impression that these are hydrogen atoms 1 Page 14 (ii) (single) covalent (bond) 1 (d) (×100) = 6 (just 6 is worth (1) mark) 1 × 100 = 6 or similar is (0) do not credit 5.8823529 and the like 1 [8] M19. 73 (seventy three) if answer is incorrect allow 1 mark for the correct proportion that H2:HCl is 1:2 and 1 mark for 36.5 [3] M20. (i) 1 Page 15 (ii) weak forces accept weak bonds 1 between molecules / intermolecular reject intramolecular 1 [3] M21. (a) (i) 2.25 correct answer gains three marks if incorrect allow 1 mark for 2 correct readings (130 and 175) and further mark for 45 ÷ 20 allow e.c.f. 3 (ii) concentration of reactant(s) lower 1 fewer collisions per second / time unit 1 (b) labour costs lower / enzymes costs lower not stop and start 1 [6] M22. (a) 10.86 accept answers between 10.64 to 10.9 if answer is incorrect allow 1 mark for rfm FeSO4 = 152 2 marks for 152 × 4/56 3 (b) 2 Fe + 3 H2SO4 → Fe2(SO4)3 + 3H2 accept other correct multiples for balancing 1 [4] Page 16 M23. (a) Quality of written communication: All scientific words used correctly (covalent, bonds, atoms) 1 any two from • large numbers of covalent bonds allow giant lattice / structure • between atoms do not accept between molecules • (covalent) bonds strong accept need much energy to break 2 (b) each carbon has 4 electrons 1 Page 17 one shared pair 1 four shared pairs 1 [6] M24. (a) 1400 1 (b) 980 correct answer gains full credit 160 tonnes Fe2O3 produces 112 tonnes Fe if incorrect allow one mark for relative formula mass iron oxide = 160 allow e.c.f. 1400 tonnes Fe2O3 will produce 1400 / 160 × 112 tonnes Fe use of 2000 tonnes Fe2O3 – deduct one mark only if working out is correct 4 [5] M25. (a) X – (metal) atom / ion 1 Y – electron 1 (b) free electrons or electrons move 1 (allow metal) atoms / ions to slide over each other OR bonding non - directional for 2 marks Page 18 1 [4] M26. 1000 × 1000 / 0.065 gains 1 mark but 15384615g (accept answer rounded to minimum of 2 sig. figures) (accept answer with no units or correct units but incorrect unit loses one mark) (answer correctly worked out in kg is acceptable) gains 2 marks [2] M27. (a) sodium hydroxide / caustic soda / NAOH for 1 mark 1 (b) negative ions move to the positive electrode etc. /because it is negative /opposite charges attract for 1 mark 1 (c) loss of electrons for 1 mark 1 [3] M28. (i) neutralise (the acid) / reduce acidity / because it is alkaline /increases pH Page 19 for 1 mark 1 (ii) CaO = 56 Ca(OH)2 = 74 each for 1 mark 2 (iii) mass = 1000 × 74/56 gains 1 mark = 1321 kg (1320 accepted) gains 2 marks (error carried forward from (ii)) 56g → 74g 1 g → 74/5 6 g (1 mark) 2 [5] M29. (a) made of layers of carbon atoms weak forces of attraction between layers (owtte) / weak vertical bonds i.e. candidate refers to the diagram layers can slide over each other layers peel off each for 1 mark (b) because there are electrons which are free (to move) reason for free electrons / each carbon atom has 3 covalent bonds each for 1 mark to max 5 [5] Page 20 M30. 56 74 each for 1 mark [2] M31. (a) some electrons from outer shells (some electrons) free to move/mobile through whole structure/between atoms/sea of electrons hold atoms together for 1 mark each or positive ions in a sea of electrons (owtte) 2 marks atoms in regular structure/layers giant structure close packed credit diagrams – look for labels for 1 mark each any 4 4 (b) (i) electrons, free to move (reference to electrons) for 1 mark each 2 (ii) layers/atoms can slide over each other for 1 mark 1 (iii) free electrons hold atoms strongly together/strong forces of attraction/bonds (between atoms)/tight packing of atoms for 1 mark 1 [8] ## (a) (2) : (6) : (2) Page 21 All 3 correct gains 2 marks 2 correct gains 1 mark 2 (b) no water present/moist air cannot enter/do not thoroughly mix/ must be in solution etc. for 1 mark 1 (c) (i) hydroxide (ion) / OH– for 1 mark 1 (ii) hydrogen (ion) / H+ for 1 mark 1 (iii) water/H2O/hydrogen oxide for 1 mark 1 [6] M33. (a) Gas A = Chlorine / Cl2 not Cl and Gas B = Hydrogen / H2 not H for 1 mark Solution C = sodium hydroxide/NaOH/spent brine for 1 mark 2 (b) (i) 2, 2 for 1 mark (ii) 2, 2 for 1 mark 2 (c) water/H2O/hydrogen oxide not hydrogen hydroxide for 1 mark 1 Page 22 (d) ions/positive ions/negative ions/cations/anions not charged particles/positive particles/negative particles not H+ / Cl-/Na+ / OHAllow hydrogen ions etc. not sulphate ions for 1 mark 1 [6] ## (a) covalent/description of covalent for 1 mark 1 (b) forces/bonds between the molecules/particles (not atoms) are weak for 1 mark each 2 (c) non-flammable so it will not burn etc. extremely unreactive so it will not react with materials in the transformer, does not conduct electricity so it can insulate the transformer gas so it has freedom to move and insulate whole area for 1 mark each 3 [6] ## (a) potassium / K for 1 mark 1 (b) carbon dioxide / CO2 for 1 mark 1 (c) losing Page 23 electrons gaining electrons for 1 mark each 4 (d) (i) power supply, (not mains) beaker containing solution, (inert) electrodes and circuit ammeter or bulb/ (or see bubbling etc. at electrodes written by drawing) for 1 mark each 4 (ii) reading on ammeter/bulb lights / (solution) conducts (electricity) bubbling / gas produced hydrogen produced chlorine / oxygen produced ions move to electrodes (must be linked to ions move) negative ions move to the positive electrode and/or positive ions move to the negative electrode negative ions lose electrons and/or positive ions gain electrons any 3 for 1 mark each 3 [13] M36. (a) C16 H34 for 1 mark 1 (b) electron gains 1 mark but shared electrons gains 2 marks 2 [3] Page 24 M37. (a) 4 HCl / 2H2O, allow multiples or fractions if whole equation balances for 1 mark 1 (b) germanium tetrachloride + water = germanium oxide + hydrochloric acid If symbol equation given it must be correctly balanced Allow germanium for 1 mark 1 (c) to purify the germanium oxide/remove impurities/give in pure product/to make pure germanium for 1 mark 1 ensure complete reaction/reaction does not give a good yield not to increase efficiency/to purify germanium for 1 mark 1 (d) (i) remove oxygen/addition of hydrogen/gain up electrons allow remove oxygen molecules (ii) GeO2 = 73 + (2 × 16) = 105 mass of germanium = 525 × (73/105) = 365 g (or alternative methods) apply consequential marking for 1 mark each 3 (e) (i) germanium is shiny/lustrous conducts a small amount of electricity * germanium oxide reacts with hydrochloric acid (and) metal oxides react with acid metal oxides are basic metal oxides are reduced by hydrogen Information must be taken from the passage. Page 25 Apply the list principle if more than three answers are given. Assume the word ‘it’ refers to the metal. any 3 for 1 mark each 3 (ii) germanium is brittle germanium tetrachloride is a (volatile) liquid made of molecules germanium tetrachloride has covalent bonding or when two non-metals react they have covalent bonding GaC14/the salt of germanium undergiven hydrolysis/reacts with water germanium is not a good conductor of electricity* * conductivity mark can only be given once any 3 for 1 mark each 3 [13] M38. (a) 2, 8, 8, 1 for 1 mark 1 (b) for 1 mark Ignore symbol in middle but structure must be drawn NOT 2,7 If covalent; can score mark for changes but not for diagram Arrow showing electron transfer from metal atom to non-metal atom = 2 marks If the ions are not identified then cannot score mark for changes Page 26 4 [5] M39. (a) (i) Na2CO3 or (Na+)2 CO32– must be completely correct for 1 mark 1 (ii) (1) decomposition of limestone or decomposition of coal or decomposition of sodium hydrogen carbonate (owtte.) allow equations even if not correctly balanced any 1 for 1 mark 1 (2) breakdown/split up not decomposed by heat for 1 mark each 2 (iii) carbon dioxide or ammonia [CO2] or [NH3] for 1 mark 1 (b) (i) zinc carbonate or zinc hydroxide allow formulae if completely correct for 1 mark 1 (ii) (zinc carbonate) is insoluble (in water) ((i) and (ii) are independent marks) for 1 mark 1 [7] M40. (a) (i) hydrogen/H2 for 1 mark Page 27 1 (ii) i.e. 2Cl¯ -2e– →Cl2 for 1 mark 1 (iii) hydroxide or OH– for 1 mark 1 (iv) sodium hydroxide/caustic soda/NaOH/bleach/ chemical name of bleach for 1 mark 1 (b) (i) Na2CO3 or (Na+)2 CO32– for 1 mark 1 (ii) coal water/H2O limestone/CaCO3/calcium carbonate any one for 1 mark 1 (iii) calcium chloride/CaCl2/sodium hydrogen carbonate/NaHCO3 for 1 mark 1 (iv) decomposition/heating of limesstone decomposition/heating of coal decomposition/heating of sodium hydrogen carbonate any 1 for 1 mark 1 described change e.g. NaHCO3 → Na2 CO3 (Use judgement) breakdown (owtte.) by heat for 1 mark each 2 (v) carbon dioxide/CO2 or ammonia/NH3 Page 28 for 1 mark 1 (c) (i) zinc carbonate/ZnCO3/zinc hydroxide/Zn(OH)2 for 1 mark 1 (ii) It is insoluble zinc carbonate is insoluble in water for 1 mark 1 [13] M41. (a) 8 marks Particularly well structured answer with most points mentioned. 7-6 marks Well structured answer. The two metals will have been compared rather than simply listing advantages/disadvantages. Most of the advantages and disadvantages of each metal have been mentioned. 5-3 marks Some structure to the answer. An attempt to compare the metals by giving some advantages and disadvantages. 2-1 marks Little structure or attempt to compare. Marks gained by listing a few advantages or disadvantages. Advantages of Nickel: Relatively low cost which makes the sparking plugs cheaper to produce. Quite high melting point which is needed because the temperature in the engine is very high. Good conductor of electricity needed to carry electricity into combustion chamber to produce spark. Page 29 Disadvantages of Nickel: Subject to corrosion in engine which means they only last a short time because nickel is higher in reactivity than platinum. Idea that this leads to reduced efficiency, unburnt petrol and air pollution. Advantages of Platinum: Less susceptible to corrosion (not corroded) because platinum is very low in reactivity. Idea that this improves efficiency and reduces pollution.Higher melting point than nickel to withstand the high temperatures in the combustion chamber. Last a lot longer than nickel electrodes due to low reactivity. (Sensible extension here could be longer service intervals etc.)Good conductor of electricity as for nickel. Extension here could be linked to the idea that the conductivity does not deteriorate as quickly as nickel.) Disadvantages of Platinum: Cost which will make the sparking plug more expensive. A good candidate might justify cost by longer life, better fuel consumption and less pollution. 8 (b) (i) giant structure/lattice/regular arrangements of atoms any for 1 mark of atoms/of ions (provided free electrons mentioned) either for 1 mark delocalised or free electrons for 1 mark 3 (ii) electrons free/can move for 1 mark each 2 [13] Page 30 M42. (a) (i) H+ + OH- → H2 O/H3O+ + OH- → 2H2 O for 1 mark 1 (ii) 1 point from e.g. smaller bits bigger surface area faster reaction dissolve faster more particles open to attack by acid any 1 for 1 mark 1 (iii) MgCO3 or MG2+CO32- or CO3 Mg for 1 mark 1 (b) (i) 2 HCl for 1 mark 1 (ii) aqueous/dissolved in water (not in solution) for 1 mark 1 (iii) CO2/gas evolved/gas has mass for 1 mark 1 (c) (i) plotting points scales curve labelling axes including units for 1 mark each 4 Page 31 (d) faster same final mass for 1 mark each 2 [12] M43. (i) neutralisation/acid base reaction for 1 mark 1 (ii) 17 (tonnes) give 80 (tonnes) (even if only in working) for 1 mark each 320 (tonnes) or alternative method) 3 marks for correct answer (if 17 and 80 not given allow 1 mark for correct answer using their figures) 3 [4] M44. (a) (i) 45% for 1 mark 1 (ii) 126 000 (consequential on (i)) for 1 mark 1 (b) (i) Cl2 = 71 1 × 71/24 or correct mathematical attempt for 1 mark (If Cl2 wrong take figure given) for 1 mark Page 32 = 2.96 kg gains 3 marks (or alternative methods) (if units not given - 3 marks. If units wrong - 2 marks) 3 (ii) any sensible eg. bleach/disinfectant/antiseptics/kill bacteria/ sterilise water/solvents/refrigerents/CFCs/PVC (not water treatment or warfare) for 1 mark 1 [6] M45. (i) 1 electrons for 1 mark (ii) covalent 1 for 1 mark (iii) made of small molecules: usually gas or liquid ) dependent on have low melting points ) having first have low boiling points ) point above forces between molecules are weak any 1 for 1 mark 3 [5] M46. (a) 40 + 12 + (3 × 16) = 100 each for 1 mark 2 Page 33 (b) Mr of CaO = 56 for 1 mark mass required = 60 × 100/56 for 2 marks = 107.1 for 1 mark 4 (c) (i) calcium hydroxide 1 (ii) solid 1 [8] M47. (a) (i) 14 electrons = gets 1 mark 2.8.4 = gets 2 marks 2 (ii) outer shell electrons 1 (iii) same number of electrons in outer shell 1 (b) (1) shiny conducts electricity (2) oxide neutralises alkalis covalent bonds 4 [8] M48. (a) any (must be named) Page 34 1 (b) F2 1 (c) –/F– 1 (d) (i) covalent 1 (ii) made of molecules etc. type of bonding when non-metals react. 1 [5] M49. (a) sodium 1 (b) neutralisation 1 (c) increase/inc. number 1 (d) H+ 1 (e) OH– (f) H+ + OH– → H2O 1 [6] M50. (a) electrolytes 1 (b) oxidation 1 Page 35 electrons lost 1 (c) 2H+ + 2e– → H2 minus sign on e– not needed 2 (d) concentration increases 1 OH– discharged from water / water decomposes 1 H+ concentration increases / H2 and O2 evolved 1 [8] M51. (a) (i) iron must be named do not accept Fe 1 (ii) hydrogen 1 and oxygen mixtures 1 burn rapidly 1 (b) (i) lowers concentration accept dilutes the acid do not accept cooling 1 less collisions (between particles) 1 (ii) H+ (aq) accept H3O+ only if 2 in front of H2O Page 36 1 OH (aq) if spectator ions correctly included on both sides, maximum = 1 mark 1 (iii) Ca(OH2) weak alkali accept NaOH strong alkali 1 Ca(OH)2 causes no problems accept NaOH causes named problem (eg caustic or exothermic or burns or corrosive) 1 [10] M53. 144 accept TiCl4 = 190 for 1 mark accept another correct step in calculation eg 570/190 = 3 for 1 mark [3] M54. (i) same number of protons and electrons accept equal numbers of protons and electrons do not accept they are neutral 1 (ii) same element accept all atoms are potassium 1 same number of protons accept same atomic number accept they all have 19+ 1 Page 37 different number of neutrons accept different mass numbers do not accept different atomic masses 1 [4] M55. (i) can be from diagram chlorine (2.8).7. accept chlorine needs one more electron 1 can be from diagram shares a pair of electrons 1 shared pair of electrons is a covalent bond do not accept ionic bond 1 (ii) can be from diagram and appropriately annotated sodium (2.8). 1. and chlorine (2.8).7 1 sodium loses one electron and chlorine gains one electron 1 Na+ and Cl– formed 1 bond formed between oppositely charged ions or ionic bond is formed do not accept covalent bond 1 [7] M56. (i) a reaction in which the products can be changed back to reactants accept a reaction that can go forwards or backwards 1 Page 38 under certain conditions 1 (ii) Mr CaCO3 = 100 1 Mr CaO = 56 1 mass of CaO = 140 (tonnes) 1 mark consequentially [5] M57. (a) (i) test: limewater accept calcium hydroxide solution 1 result: ‘goes’ cloudy accept white or milky do not accept misty or chalky test must be correct before result mark can be considered 1 (ii) 2 NaHCO3 + H2SO4 → Na2SO4 + (2) H2O + (2) CO2 1 correctly balanced 1 (b) (i) H+ + OH– 1 → H2O deduct one mark if incorrectly balanced accept H3O+ instead of H+ then 2H2O needed for balance 1 Page 39 (ii) pH increases accept numerical indication 1 (c) addition of sulphuric acid 1 correct use of an indicator accept idea of forming a neutral solution 1 crystallisation (of neutral solution) accept description using evaporation 1 [10] M58. (a) calcium atom loses two electrons accept diagrams with correct labelling 1 (each) fluorine atom gains one electron accept two electrons transfer from a calcium atom to the two fluorine atoms for these first two marks 1 forming full (outer) shells of electrons accept forming full (outer) energy levels or noble gas electronic structures do not accept stable unless qualified 1 giving the ions Ca2+ and F 1 attraction between ions of opposite charges accept electrostatic attraction between ions if candidate mentions sharing or pairing of electrons then no credit if explanation is entirely correct but they state this is called covalent bonding, the maximum mark is four 1 (b) atoms of the same element Page 40 1 atomic number is same accept each contains 92 or same number of protons 1 mass numbers differ or each has a different number of neutrons 1 one has 146 neutrons the other has 143 neutrons accept one has three more or less neutrons than the other 1 (c) (i) 349 1 (ii) 349g UF2 produces 235g U [1] first mark can be awarded if answer is incorrect answer = 117.5 1 [12] M59. (i) electrolysis 1 (ii) oxidation 1 (iii) hydroxide ions or OH– accept sodium hydroxide or hydroxide or OH for one mark only 2 (iv) H+ + e– 1 H2 ignore any state symbols 1 2H+ + 2e– → H2 Page 41 accept H+ + e-→ H for one mark only 1 [7] M60. answers apply to: accept diagrams and/or descriptions carbon dioxide CO2 ammonia NH3 methane CH4 water H2O *outer electronic structure of one atom correct or needs correct number of electrons to complete outer shell 1 *outer electronic structure of other atom correct or needs correct number of electrons to complete outer shell 1 *one shared pair of electrons (as one covalent bond) use of ions or reference to ionic bonding negates this mark 1 *outer electronic structure of compound correct or each atom now has a full outer shell/noble gas electron structure 1 [4] M61. 352 g gains 3 marks (moles C8H18 = 114 / 114 = 1 mole) moles CO2 = 8 (1) mass CO2 = 8 × 44 (1) = 352 g (1) 1 mark for each point Page 42 (ecf allowed between parts) or 114 → 8 (1) × 44 (1) 114 → 352 g (1) ecf allowed between parts [3] M62. hydrogen ions (from acid) or protons / H+ 1 react with hydroxide ions (from alkali) / OH 1 to produce water H + OH H2O gains all 3 marks ignore state symbols molecules of hydrogen ions and molecules of hydroxide ions produce water = 2 marks if they fail to get any of the above marks they can get 1 mark for neutralisation / product neutral 1 [3] M63. (a) Mr (SiO2) = 60 if Mr incorrect ecf for max 2 1 60 g SiO2 → 28 g Si correct answer for 3 marks 1 2.14 g SiO2 → 1 g Si allow 2, 2.1, 2.14 (or anything rounding to 2.14), 2.16 or 2.2 a unit is not required but an incorrect unit loses the third mark Page 43 OR Mr (SiO2) = 60 (1) moles if silicon needed = = 0.0357 mass of SiO2 needed = 0.0357 × 60 (1) = 2.14 g (1) allow 2, 2.1, 2.14 (or anything rounding to 2.14), 2.16 or 2.2 OR Mr (SiO2) = 60 (1) mass SiO2 = 1 × (1) = 2.14 g (1) allow 2, 2.1, 2.4 (or anything rounding to 2.14), 2.16 or 2.2 3 (b) (i) MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l) penalise incorrect symbols correctly balanced equation for 1 mark state symbols for 1 mark allow correct multiples / fractions 2 (ii) or ignore inner shell electrons of silicon allow correct drawings without symbols must clearly indicate four shared pairs of electrons with one electron from each atom Page 44 (iii) Si H 1 = 0.05 = 0.15 1 1 3 for whole number ratio can be implied 1 Si H3 accept H3 Si or any correct formula with 1:3 ratio if in step 1 they get either of ratios incorrect they lose first 2 marks but can be ecf for 3rd and 4th mark evidence of mass / Ar 1 mark proportions of each 1 mark whole number ratio 1 mark correct formula 1 mark 1 (iv) C accept c 1 (c) any four from: • giant structure / macromolecule / lattice / giant molecule allow giant molecular / giant atomic structure • each silicon atom joined to four other atoms (or diagram) • covalent bonds • bonds are strong or large amount of energy needed to break bonds accept hard to break bonds • large number of bonds to be broken mention of giant ionic structure or intermolecular forces or intermolecular bonds max 1 mark diamond or carbon discussion max 3 marks unless clearly linked to silicon 4 [15] Page 45 168g → 44g M64. 1 1g → 1 11g → 2.88g (2.9g) care with rounding 1 or Mr values 84 and 44 (1) moles hydrogen carb = (1) mass of CO2 = = 2.9g answer 2.88 to 2.9 gets 3 marks answer of 3 gets 2 marks (1) [3] M65. (a) (i) Quality of Written Communication The answer to this question requires ideas in good English in a sensible order with correct use of scientific terms. Quality of written communication should be considered in crediting points in the mark scheme. maximum 2 marks if ideas not expressed well layers / lattice / giant structure / regular pattern of atoms (diagram) allow layers / lattice / giant structure / regular pattern of ions do not accept particles 1 outer (shell) electrons accept valence electrons 1 (free to) move (through whole structure) accept delocalised / mobile / free Page 46 1 (ii) the free electrons (allow the metal to conduct electricity) accept electrons move / mobile / delocalised 1 (iii) atoms / ions / layers can slide / slip / move over each other 1 (b) (i) copper oxide formed or Cu reacts with oxygen or Cu is oxidised 1 this is a poor conductor or gets in the way of free moving electrons or fewer mobile electrons do not accept electricity 1 or oxygen atoms / oxygen molecules / oxide ions in metal do not accept oxygen pockets / bubbles prevents / disrupts flow of electrons / current or fewer mobile electrons (1) do not accept macro explanations do not accept electricity (ii) hydrogen reacts with oxygen or water is formed or hydrogen reduces copper oxide etc. 1 [8] M66. (a) H+(aq) + OH– (aq) → H2O(l) or H3O+(aq) + OH–(aq) → H2O(l) mark for correct equation mark for state symbols any other symbols = 0 marks accept correct spectator ions e.g. Na+(aq) + OH– (aq) + H+(aq) + Cl– (aq) → Na+(aq) + Cl– (aq) Page 47 + H2O(l) 2 (b) (i) nitric acid and ammonia (solution) HNO3 NH3 / NH4OH mark for both accept ammonium hydroxide / NH4OH instead of ammonia do not accept ammonia hydroxide do not accept hydrogen nitrate solution accept correct formulae 1 (ii) provides oxygen or oxidising (agent) or oxidant do not accept it contains oxygen alone or rich in oxygen 1 [4] M67. (a) 2.8.3 on diagram as Xs / dots or e accept paired or unpaired 1 (b) any two from: • electrons in highest energy level or electrons in outer shell • electrons are delocalised or sea of electrons • electrons are free or electrons move around / flow • electrons carry charge / current ignore carry electricity 2 [3] Page 48 M68. (a) nanoparticles / they are small(er) accept 1–100 nm or a few atoms in size 1 so can easily pass through pores / skin / cell / membranes / arteries / veins / capillaries / into blood stream owtte must be a comparative statement can be inferred from smaller particles allow absorbed for pass through 1 (b) any one from: • may be toxic (to cells / specific cells) allow may harm / damage / kill cells / organs / tissues or may cause cancer • to ensure safety or reduce risk or risk of litigation allow may cause allergies / side effects ignore harmful / dangerous unqualified eg harmful to body / people • nanoparticles may have different properties • to see if they pass into the body 1 (c) any two sensible ideas from eg: • testing is expensive or testing costs money allow it costs money ignore litigation • testing is time consuming • don’t see any reason to test since normal sized particles (of titanium oxide) do not cause harm accept normal sun cream does not cause harm owtte • don’t want to risk not producing a popular product (owtte) eg if unsafe will have to stop production or have to remove product if toxic • testing process / unfavourable results might cause alarm / reduce sales / reduce profit (less money) • do not want to be seen doing animal testing Page 49 2 [5] M69. Pb 76 207 Cl 13 35.5 C O 2.2 8.8 12 16 1 mark for dividing one mass by Ar allow upside down ratio to lose this mark only 1 = 0.367 = 0.366 = 0.183 = 0.55 1 mark for one correct proportion – accept to one d.p. or rounded up to 1 d.p. 1 1 mark for all four correct proportions correctly rounded 1 2 2 1 3 or Pb2Cl2CO3 1 mark for correctly written formula or correct whole number ratio correct formula without working gets only 1 mark. e.c.f. can be allowed from incorrect proportions to formula or ratio 1 [4] M70. any four points from: • high melting point owtte ignore boiling point • many or all atoms joined together • each silicon (atom) joined to four oxygen (atoms) or each oxygen joined to two silicon • covalent (bonds) Page 50 • many bonds would need to be broken • strong bonds allow hard to break bonds • lot of energy / heat needed to break bonds allow high temperature needed to break bonds • giant / macromolecular / lattice / diamond structure • unreactive allow doesn’t react with materials within furnace = 1 mark • rigid / hard structure • no free electrons • poor conductor of heat giant covalent structure = 2 marks max 3 if ionic / metallic bonding mentioned ignore electrostatic ignore molecules / intermolecular forces [4] M71. (a) Compound A any one from: accept correct formulae • sodium bromide • potassium bromide • ammonium bromide • hydrogen bromide • any metal bromide except silver and lead. 1 Compound B silver nitrate accept silver sulphate 1 (b) the silver compound will decompose / silver ions be reduced to silver (owtte) Page 51 accept film would darken owtte accept any idea of light changing silver bromide / silver ions / silver nitrate / silver sulphate allow ‘forms a black solid’ / it would turn black 1 (c) precipitation accept descriptions of precipitation reactions accept double decomposition accept precipitate do not allow displacement 1 (d) electrons 1 are gained the second mark must be linked to electrons accept it / silver / silver ions gains electrons for both marks ignore references to oxygen 1 [6] M72. (a) 2Mg + O2 → 2MgO accept correct multiples / fractions 1 (b) electrons do not need to be paired accept dots / circles / e instead of crosses Page 52 do not allow 2.6 without diagram 1 (c) electrons do not need to be paired allow without bracket s/ must have the charge accept dots / circles / e instead of crosses ignore extra empty outer shells ignore nucleus do not allow [2.8]2+ without diagram 1 (d) oppositely charged (ions / atoms) allow positive and negative(ions / atoms) 1 (they) attract must be in correct context accept held by electrostatic forces ignore ionic bonding maximum 1 if they refer to intermolecular forces / attractions / covalent bonds 1 (e) magnesium chloride accept MgCl2 (if correctly written) 1 [6] Page 53 M73. (a) C 0.60 H 0.15 O 0.40 1 12 1 = 0.05 = 0.15 16 = 0.025 1 2 6 1 1 C2H6O 1 mark for dividing the correct amount or multiples of correct amount by Ar 1 mark for proportions 1 mark for whole number ratio – accept any multiple 1 mark for correctly written simplest formula correct formula without working gets only 2 marks correct formula gains full marks provided steps 1 and 2 are correct. ecf can be allowed from step 2 to 3 or step 3 to 4 formula can be in any order eg OH6C2 1 (b) intermolecular forces / bonds 1 are weak (covalent) bonds are weak = 0 or forces between molecules or bonds between molecules (1) (attractive) forces are weak = 1 are weak (1) if no marks awarded, allow low boiling point or small Mr for 1 mark 1 (c) (i) to check the safety of the perfume (owtte) accept references to possible harmful / dangerous effects of perfume or possible reactions on skin eg to show it does not damage skin / cause cancer etc. allow to see what it smells like on the skin allow so the company do not have to test on animals 1 Page 54 (ii) any two from: idea from text linked with an explanation • the company claim to have tested the product: but we cannot be certain they have or how thorough they are or how accurately reported • companies did not disclose how they did their tests: so they could not be checked or so they could not be shown to be reliable / valid or so they could not be repeated or converse eg companies should disclose how they did their tests so that results can be checked etc. • companies may not have repeated their tests: so they may not be reliable • companies do their own tests: so they may be biased or so they may not be truthful about their results or so they may not be reliable or converse eg independent tests should be done so as to ensure there is no bias etc. • the companies are using different tests: so the results cannot be compared or so results will be different or so results will not be fair / valid / reliable or converse eg companies should do the same tests so that the results will be fair etc. • companies would not give false information because of damage to reputation or it might lead to litigation 2 [9] M74. (a) (i) any one from: • they are positive / cations • they are H+ • opposite charges attract ignore atom 1 Page 55 (ii) potassium is more reactive (or reverse) assume ‘it’ refers to hydrogen allow potassium reacts with water allow potassium is very reactive or most reactive metal / element allow hydrogen gains electrons more easily / is reduced more easily accept potassium is higher up the reactivity series 1 (b) 6 and 2 accept correct multiples and fractions 1 (c) (i) the reaction / it is reversible or a description of a reversible reaction allow ‘it is an equilibrium’ allow reversible symbol drawn correctly allow ‘the reverse / back reaction’ 1 (ii) lithium nitride assume that ‘it’ or if they do not specify means lithium nitride assume lithium / lithium nitrate refers to lithium nitride • hydrogen is bonded / held / absorbed / has formed a compound / reacted with lithium nitride 1 plus one of: • does not explode / cause a fire • is not free / less hydrogen • is not under pressure • does not leak • is only released slowly 1 • compound of hydrogen with lithium nitride / product is (more) stable / less reactive / less chance of a reaction accept converse for hydrogen as below assume that gas / hydrogen means gas in the cylinder • hydrogen (in cylinder) / gas is not bonded / held Page 56 absorbed / in a compound / reacted with lithium nitride 1 plus one of: • can explode / cause a fire • is free • is under pressure • can leak • releases quickly 1 (d) (i) loss of an electron or loses electrons do not accept any ref. to oxygen 1 (ii) full outer shell of 8 electrons on circle need not be paired can be ×, dot or e do not accept if extra electrons added to inner shell 1 [10] M75. (a) (i) any one from: • they are positive / cations • they are H+ • opposite charges attract ignore atom 1 (ii) potassium is more reactive (or reverse) assume ‘it’ refers to hydrogen allow potassium reacts with water allow potassium is very reactive or most reactive metal / element allow hydrogen gains electrons more easily / is reduced Page 57 more easily accept potassium is higher up the reactivity series 1 (b) 6 and 2 accept correct multiples and fractions 1 (c) (i) the reaction / it is reversible or a description of a reversible reaction allow ‘it is an equilibrium’ allow reversible symbol drawn correctly allow ‘the reverse / back reaction’ 1 (ii) lithium nitride assume that ‘it’ or if they do not specify means lithium nitride assume lithium / lithium nitrate refers to lithium nitride • hydrogen is bonded / held / absorbed / has formed a compound / reacted with lithium nitride 1 plus one of: • does not explode / cause a fire • is not free / less hydrogen • is not under pressure • does not leak • is only released slowly 1 • compound of hydrogen with lithium nitride / product is (more) stable / less reactive / less chance of a reaction accept converse for hydrogen as below assume that gas / hydrogen means gas in the cylinder • hydrogen (in cylinder) / gas is not bonded / held absorbed / in a compound / reacted with lithium nitride 1 plus one of: • can explode / cause a fire Page 58 • • • • is free is under pressure can leak releases quickly 1 (d) (i) loss of an electron or loses electrons do not accept any ref. to oxygen 1 (ii) full outer shell of 8 electrons on circle need not be paired can be ×, dot or e do not accept if extra electrons added to inner shell 1 [10] Page 59