Structure and Bonding-P1

Transcription

1 Structure and Bonding-P Mark Scheme Level Subject Exam Board Unit Topic Difficulty Level Booklet GCSE Chemistry AQA C2 Structure and Bonding-P Gold Level Mark Scheme Time Allowed: 25 minutes Sce: /25 Percentage: /00 Page

2 M.(a) lattice / giant structure max 3 if increct structure bonding particles ionic (contains) ions Na + and Cl - accept in wds dot and cross diagram: must include type and magnitude of charge f each ion electrostatic attraction allow attraction between opposite charges (b) hydrogen allow H 2 sodium hydroxide allow NaOH (c) any one from, eg: people should have the right to choose insufficient evidence of effect on individuals individuals may need different amounts. allow too much could be harmful igne religious reasons igne cost igne reference to allergies (d) (i) one bonding pair of electrons accept dot, cross e any combination, eg Page 2

3 (iii) 6 unbonded electrons on each atom simple molecules max 2 if increct structure bonding particles accept small molecules accept simple / small molecular structure with intermolecular fces accept fces between molecules must be no contradicty particles which are weak which require little energy to overcome must be linked to second marking point reference to weak covalent bonds negates second and third marking points iodine has no delocalised / free / mobile electrons ions so cannot carry charge if no mark awarded iodine molecules have no charge gains mark [4] M2.(a) (i) any two from: igne any conclusion drawn referring to data below 7.5 nm above 20 nm 00% of (type and type 2) bacteria are killed with a particle size of 7.5 to 8.5 nm accept nanoparticles in the range of 7.5 to 8.5 nm are most effective at killing (type and type 2) bacteria as the size increases (beyond 8.5 nm), nanoparticles are less effective at killing (type and type 2) bacteria type shows a linear relationship type 2 is non-linear type bacteria me susceptible than type 2 (at all sizes of nanoparticles shown on the graph) allow type 2 bacteria are harder to kill 2 (yes) because you could confirm the pattern that has been observed allow would reduce the effect of anomalous points / random errs allow would give better line of best fit Page 3

4 igne references to reliability / precision / accuracy / reproducibility / repeatability / validity (b) (no) because trend / conclusion is already clear magnesium loses electron(s) oxygen gains electron(s) two electrons (per atom) gives full outer shells (of electrons) eight electrons in highest energy level reference to increct particles increct bonding increct structure = max 3 (electrostatic) attraction between ions fms ionic bonds accept noble gas structure [7] M3.(a) weaker bonds allow (other substances) react with the silicon dioxide fewer bonds igne weaker / fewer fces disruption to lattice do not accept reference to intermolecular fces / bonds (b) (i) Na 2O do not accept brackets charges in the fmula Page 4

5 electrons can be shown as dots, crosses, e any combination (c) 2 bonding pairs accept 4 electrons within the overlap 2 lone pairs on each oxygen accept 4 non-bonding electrons on each oxygen lattice / regular pattern / layers / giant structure / close-packed arrangement (of) positive ions (of) atoms (with) delocalised / free electrons reference to increct particles increct bonding increct structure = max 2 [7] M4.(a) Will kelp last longer than coal as an energy source? (b) any two from: cannot be determined by experiment allow can t predict how long kelp / coal will last allow me testing needed based on opinion ethical environmental economic reason allow could damage ecosystem allow reference to cost 2 (c) (i) 7 Page 5

6 sodium (atom) loses (electron) and iodine (atom) gains (an electron) reference to increct bonding increctly named particle = max 2 any all marks can be obtained from a labelled diagram igne inner shell electrons if shown electron (electrostatic) attraction fms ionic bond(s) (iii) ions can move (in the solution) (iv) 2 I I e (v) hydrogen is fmed because sodium is me reactive (than hydrogen) [] M5.(a) reference to increct bonding increct structure increct particles = max 3 giant structure / lattice igne many bonds Page 6

7 made up of positive ions surrounded by delocalized / free electrons allow positive ions surrounded by a sea of electons with strong bonds / attractions allow hard to break f strong so a lot of energy is needed to break these bonds / attractions / fces igne high temperature igne heat (b) (i) that they are very small -00 nanometres a few(hundred) atoms accept tiny / really small / a lot smaller / any indication of very small eg. microscopic, smaller than the eye can see igne increct numerical values if very small is given delocalised / free electrons allow sea of electrons one non-bonded electron from each atom accept electron(s) moving through the structure / nanotube allow electron(s) carry / fm / pass current / charge [7] Page 7

8 M6.(a) (i) lead nitrate accept Pb(NO 3) 2 do not accept nitrideigne (all) nitrate(s) sodium iodide / potassium iodide accept Nal / Kl accept other crect soluble iodides eg HI, MgI 2 do not accept sodium iodine / potassium iodine (b) metallic / sharing / covalent molecule = max 3 magnesium loses 2 electrons all three underlined ideas must be present two underlined ideas = mark eg magnesium loses electronsmagnesium gains 2 electronsmagnesium loses 2 ions nb magnesium ion loses 2 electrons = mark 2 errs = 0 marks eg magnesium gains electrons 2 iodine gains / an electron all four underlined ideas must be present three underlined ideas = mark eg iodine gains electron(s) iodine loses / an electroniodide gains / an ioniodide (ion) gains / an electron 2 errs = 0 marks 2 (c) attractions / fces (of attraction) / bonds are strong lot of energy needed to break bonds / fces / attractions max 2 if reference to increct bonding increct structure increct particles because oppositely charged ions attract electrostatic attraction between ions Page 8

9 in giant structure lattice igne many bonds igne ionic bonding unqualified [9] M7.(a) (i) M r of NH 3 = 7 crect answer with without wking gains 3 marks accept crect rounding of intermediate answers can be credited from crect substitution from step 2 2 (moles of) NH 3 = (28/34) 6.8 allow ecf from step (4/7) 6.8 = 5.6 allow ecf from step 6.8 accept Page 9

10 crect answer with without wking gains 2 marks if answer is not crect evidence of 4.2 / gains mark if answer not crect gains mark 2 (iii) reaction is reversible accept reaction reaches equilibrium allow reaction does not reach completion igne some is lost (b) 3 bonding pairs do not accept extra electrons on hydrogen lone pair accept 2 non-bonding electrons on outer shell of nitrogen (c) (i) hydroxide / OH accept phonetic spelling neutralisation accept acid-base allow exothermic (iii) nitric (acid) allow HNO 3 igne increct fmula (iv) (NH 4 ) 2 SO 4 Page 0

11 allow (NH 4 + )2 SO42 [2] M8.(a) (i) current / charge couldn t flow allow could not conduct (electricity) because the ions / particles couldn t move do not accept electrons/ molecules / atoms (salt) needs to be molten / () dissolved (to conduct electricity) so that the ions / particles can move () do not accept electrons / molecules / atoms he had status accept he had authity experience he had evidence / proof accept the experiment could be repeated (b) hydrogen / H 2 do not allow hydrogen ions the ions are positive accept because opposite (charges) attract potassium is me reactive (than hydrogen) Page

12 accept potassium ions are less easily discharged (than hydrogen) potassium ions are less easily reduced (than hydrogen) (c) (i) gain electron(s) accept fully balanced crect equation f 2 marks one electron if no other marks awarded allow (potassium ions) reduced f mark 2 Cl Cl 2 + 2e must be completely crect, including charge on electron accept crect multiples (iii) 2, 8, 8 accept any combination of dots, crosses, e any other relevant symbol igne any charges if given [0] M9. (a) (i) mention of molecules / intermolecular / ionic / covalent = max 2 atoms / positive ions any two from: (atoms / positive ions) in regular pattern / lattice / layer / giant structure ( diagram) delocalised electrons Page 2

13 accept electrons move within / through the structure allow free (moving) electrons allow sea of electrons (atoms / positive ions) held together by strong / electrostatic attractions allow strong (metallic) bonds 2 delocalised electrons accept electrons move within / through the structure allow free electrons (b) (i) smaller / very small accept converse accept - 00 nanometres in size accept a few hundred atoms accept larger surface area large surface area f their size nanoparticles / me can fit into (tiny) gaps allow nanosize particles have large(r) surface area [6] M0. (a) (i) ionic / molecules / metallic / (inter)molecular = max 2 because graphene / it has a giant structure / lattice / macromolecular accept all / every / each atom is bonded to 3 other atoms because graphene / it has covalent bonds / is covalent Page 3

14 because in graphene / the bonds are strong a lot of energy needed / hard to break the bonds there are delocalised / free electrons because one (delocalised / free) electron per atom linked to first marking point accept because three electrons per atom used (in bonding) accept because one electron per atom not used (in bonding) (b) opaque (owtte) eg could not see through them layers slide layers not aligned igne thick [6] M. (a) 8 (b) it loses / transfers electrons it = Au / gold atom three electrons sharing / covalency = max mark Page 4

15 (c) (i) O 2 2 CO and 2 CO 2 crect balancing of equation from O accept crect multiples / fractions throughout reference to increct bonding = mark max because carbon dioxide is simple molecular / small molecules there are intermolecular fces (between the molecules) allow intermolecular bonds so a small amount of energy needed (to separate molecules) (intermolecular fces) are weak (d) any three from: gold is the only catalyst f some reactions catalysts are not used up improves speed of reaction reduces amount of energy process needs low(er) temperature if no mark awarded, allow catalyst reduce costs (of the process) f mark only small quantities (of catalyst) needed 3 [] Page 5

16 M2. (a) because calcium is +2 and hydroxide is accept to balance the charges to make the compound neutral (in terms of charges) allow calcium needs to lose 2 electrons and hydroxide needs to gain one electron (b) particles of size -00 nm allow clear comparison to nmal size particles particles with a few hundred atoms / ions particles with a high surface area (to volume ratio) as different properties to nmal size particles of the same substance (c) M r CaO = 56 and M r Ca(OH) 2= 74 2/56 (x74) (x74) allow ecf from step 74/56 (x2).3(24 ) (x2) 2.6(428 ) in range 2.6 to 2.96 crect answer with without wking gains 3 marks allow ecf carried through from step igne final rounding to 3 Page 6

17 [5] M3. (a) Graphite: because the layers (of carbon atoms) in graphite can move / slide it = graphite this is because there are only weak intermolecular fces weak fces between layers accept Van der Waals fces allow no covalent bonds between layers Diamond: however, in diamond, each carbon atom is (strongly / covalently) bonded to 4 others allow diamond has three dimensional / tetrahedral structure so no carbon / atoms able to move / slide allow so no layers to slide so diamond is rigid (b) because graphite has delocalised electrons / sea of electrons allow free / mobile / roaming electrons which can carry charge / current move through the structure however, diamond has no delocalised electrons Page 7

18 accept however, diamond has all (outer) electrons used in bonding [7] M4. any three from: any reference to increct bonding = max 2 giant structure / lattice / macromolecule covalent (bonds) bonds are (very) strong allow bonds difficult to break takes a lot of energy to break bonds each atom / carbon joined to four others accept each atom / carbon fms four bonds 3 [3] M5. (a) (i) mention of molecules any reference to increct bonding = max 2 giant structure / lattice particles arranged in a regular pattern allow close packed / layers sea of electrons / delocalised electrons allow free electrons positive ions and electrons attract each other Page 8

19 igne metallic bonds appropriately labelled diagrams can gain first two marks (sea of) electrons can move through the structure allow free / roaming / mobile electrons delocalised electrons (b) (metal) oxide / ionic compound fmed ions not free to move electrons cannot move through the structure allow no / fewer delocalised / free / roaming / mobile electrons [6] M6. three from: reference to ionic / metallic / intermolecular / (small) molecules = max 2 structure: (max 2) giant structure / macromolecule / all the atoms are joined together allow (giant) lattice igne large structure igne diamond structure covalent (bonds) strong bonds / bonds difficult to break each silicon atom fms 4 bond sand / each oxygen atom fms 2 bonds explanation: (max 2) Page 9

20 a lot of energy needed to break the bonds high melting point if neither point given accept high temperature needed to break bonds f mark does not burn react with oxygen 3 [3] M7. (a) mark f dividing mass by A r max 2 if A r divided by mass = 0.03 = 0.04 mark f crect proptions 3 4 mark f crect whole number ratio (allow multiples) can be awarded from crect fmula Pb 3O 4 mark f crect fmula ecf allowed from step 2 to step 3 and step 3 to step 4 if sensible attempt at step crect fmula with no wking gains 2 marks Page 20

21 (b) (i) allow all dots all crosses e e igne inner shells and any inner electrons allow 4 non-bonded electrons anywhere on shell as long as not in overlap need not be paired fces of attraction / bonds between molecules are weak (owtte) do not accept intramolecular fces / covalent bonds are weak do not accept reference to ions intermolecular fces / bonds are weak (owtte) it is made of small molecules with weak fces of attraction if 2 marks not awarded made of small molecules / simple molecular gains mark fces of attraction are weak (without specifying between molecules / intermolecular) gains mark (accept easily broken / not much energy needed to break instead of weak) bonds are weak without specifying intermolecular would not gain a mark and would be igned 2 (iii) 4 [8] M8. (a) any four from: max 3 marks if any reference made to covalent / ionic Page 2

22 bonding / molecules intermolecular fces graphite / diamond fces of attraction between electrons and then igne throughout giant structure / lattice igne layers positive ions sea of electrons delocalised / free electrons igne electrons can move awareness of outer shell / highest energy level electrons are involved (electrostatic) attractions / bonds between electrons and positive ions bonds / attractions (between atoms/ ions) are strong allow hard to break f strong igne fces unqualified a lot of energy / heat is needed to break these bonds / attractions igne high temperature 4 (b) (i) that they are very small accept tiny / really small / a lot smaller / any indication of very small eg microscopic, smaller than the eye can see 00 nanometres a few (hundred) atoms igne increct numerical values if very small is given any 2 from: one (non-bonded) electron from each atom delocalised / free electrons allow sea of electrons igne electrons can move electron carry / fm / pass current / charge igne carry electricity 2 [7] Page 22

23 M9. (a) (i) lead nitrate accept Pb(NO 3) 2 do not accept nitride sodium iodide / potassium iodide accept NaI / KI accept other crect soluble iodides do not accept sodium iodine / potassium iodine filter / filtration / filtering accept decant / decanting etc. accept centrifugation igne evapation heating if after filtration (b) metallic / sharing / covalent molecule = max 3 magnesium loses 2 electrons all three underlined ideas must be present two underlined ideas = mark eg magnesium loses electrons magnesium gains 2 electrons magnesium loses 2 ions nb magnesium ion loses 2 electrons = mark 2 errs = 0 marks eg magnesium gains electrons all four underlined ideas must be present 2 iodine gains / an electron Page 23

24 three underlined ideas = mark eg iodine gains electron(s) iodine loses / an electron iodine gains / an ion iodide (ion) gains / an electron 2 errs = 0 marks 2 (c) any two from: mention of molecules / intermolecular / covalent / atoms = max fces (of attraction) / bonds are strong lot of energy needed to break bonds oppositely charged ions attract electrostatic attraction between ions giant structure lattice allow many bonds igne ionic bonding unqualified 2 [9] M20. (a) one nitrogen atom joined to three hydrogen atoms crect pairs of electrons (b) because ammonia is made of small molecules / simple molecules / simple molecular structures and so there are weak fces between the molecules and so the intermolecular fces are weak incomplete answers that link only size of molecule strength of intermolecular fces with boiling point only gain mark Page 24

25 (c) (i) hydroxide nitric (d) because this is an endothermic reaction that takes in energy from the surroundings as the ammonium nitrate dissolves [8] M2. heat then mould / extrude into a new shape / object plastic made of polymer chains that can move (when heated) because plastic / polymer has weak intermolecular fces [4] M22. (a) the sodium atom loses / transfers an / one electron the chline atom gain(s) this / an / one electron Page 25

26 involves electrons in the outer energy levels / shells of both the sodium atom and the chline atom (b) sodium chlide has a giant structure / lattice of oppositely charged ions / positive and negative ions the electrostatic fces of attraction / bonds between ions are strong therefe sodium chlide has a high melting point because a large amount of energy is needed to make the ions mobile [6] M23. (a) allow all dots all crosses combination all e / e other suitable symbols centre of symbols must be on inside overlapping areas within reason (b) (i) any two from: no change initially stays constant at the beginning Page 26

27 increase slowly at first and then me rapidly accept converse arguments allow vapour pressure is 0 at any temperature < 00 o C f mark accept positive crelation accept explanation based on kinetic they eg particles have me kinetic energy allow reasonable attempt at using numbers 2 44 (using graph) accept 43 to 45 (c) intermolecular fces / bonds fces / bonds between molecules bonds / fces are weak covalent bonds are weak = 0 marks if they do not gain either of the marks on the left then allow simple covalent / molecular / made of small molecules f mark [6] M24. (a) 2.6 / range 2.5 to 2.7 crect answer with without with wrong wking gains 2 marks (accept answers between 2.5 and 2.7) if answer increct moles of salicylic acid = 2/38 = moles ie 2/ gains mark (80/38) 2 gains mark g 80/38 = (.304 g) gains mark (not.304g alone) 2 Page 27

28 (b) 42. range 40.7 to 42.3 accept crect answer with without with wrong wking f 2 marks ecf ie (. / their answer from (a)) 00 crectly calculated gains 2 marks if answer increct percentage yield =. / gains mark if they do not have an answer to part (a) they choose not to use their answer then: yield = (. / 2.5) 00 () = 44 accept 44 f 2 marks with no wking 2 (c) any one from: errs in weighing some (of the aspirin) lost do not allow lost as a gas not all of the reactant may have been converted to product eg reaction didn t go to completion allow loss of some reactants the reaction is reversible accept other products / chemicals side reactions igne waste products reactants impure not heated f long enough not hot enough f reaction to take place (d) any one from: use lower temperature Page 28

29 use less fuel / energy igne references to use of catalyst produce product faster speed up reaction me product produced in a given time (owtte) increased productivity lowers activation energy [6] M25. five ideas from the following f one mark each each carbon / atom joined / bonded to three other carbon / atoms each carbon fms 3 bonds in layers only weak fces (of attraction) / bonds between layers allow weak electrostatic / intermolecular fces /bonds between layers layers / atoms can slide over each other one electron on each carbon is not used f bonding electrons delocalised electrons free allow sea of electrons electrons carry the charge / current giant structure / lattice covalent (bonds) strong bonds a lot of energy needed to break bonds reference to ionic bonding = max 4 diagrams could be used: to show layered structure to show that each carbon is bonded to three other carbon atoms to show giant structure (at least 3 rings required) [5] Page 29

30 M26. (a) (i) any one from: they are positive / cations they are H + opposite charges attract igne atom potassium is me reactive ( reverse) assume it refers to hydrogen allow potassium reacts with water allow potassium is very reactive most reactive metal / element allow hydrogen gains electrons me easily / is reduced me easily accept potassium is higher up the reactivity series (b) 6 and 2 accept crect multiples and fractions (c) (i) the reaction / it is reversible a description of a reversible reaction allow it is an equilibrium allow reversible symbol drawn crectly allow the reverse / back reaction lithium nitride assume that it if they do not specify means lithium nitride assume lithium / lithium nitrate refers to lithium nitride Page 30

31 hydrogen is bonded / held / absbed / has fmed a compound / reacted with lithium nitride 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 compound of hydrogen with lithium nitride / product is (me) stable / less reactive / less chance of a reaction accept converse f hydrogen as below assume that gas / hydrogen means gas in the cylinder hydrogen (in cylinder) / gas is not bonded / held absbed / in a compound / reacted with lithium nitride plus one of: can explode / cause a fire is free is under pressure can leak releases quickly (d) (i) loss of an electron loses electrons do not accept any ref. to oxygen full outer shell of 8 electrons on circle need not be paired can be, dot e do not accept if extra electrons added to inner shell [0] Page 3

32 M27. (a) C H O = 0.05 = 0.5 = C 2H 6O mark f dividing the crect amount multiples of crect amount by A r mark f proptions mark f whole number ratio accept any multiple mark f crectly written simplest fmula crect fmula without wking gets only 2 marks crect fmula gains full marks provided steps and 2 are crect. ecf can be allowed from step 2 to 3 step 3 to 4 fmula can be in any der eg OH 6C 2 (b) intermolecular fces / bonds are weak (covalent) bonds are weak = 0 fces between molecules bonds between molecules () (attractive) fces are weak = are weak () if no marks awarded, allow low boiling point small M r f mark (c) (i) to check the safety of the perfume (owtte) Page 32

33 accept references to possible harmful / dangerous effects of perfume 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 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 how though they are how accurately repted companies did not disclose how they did their tests: so they could not be checked so they could not be shown to be reliable / valid so they could not be repeated 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 so they may not be truthful about their results so they may not be reliable 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 so results will be different so results will not be fair / valid / reliable converse eg companies should do the same tests so that the results will be fair etc. companies would not give false infmation because of damage to reputation it might lead to litigation 2 [9] Page 33

34 M28. (a) 2Mg + O 2 2MgO accept crect multiples / fractions (b) electrons do not need to be paired accept dots / circles / e instead of crosses do not allow 2.6 without diagram (c) electrons do not need to be paired allow without bracket s/ must have the charge accept dots / circles / e instead of crosses igne extra empty outer shells igne nucleus do not allow [2.8] 2+ without diagram (d) oppositely charged (ions / atoms) allow positive and negative(ions / atoms) Page 34

35 (they) attract must be in crect context accept held by electrostatic fces igne ionic bonding maximum if they refer to intermolecular fces / attractions / covalent bonds (e) magnesium chlide accept MgCl 2 (if crectly written) [6] M29. any four points from: high melting point owtte igne boiling point many all atoms joined together each silicon (atom) joined to four oxygen (atoms) each oxygen joined to two silicon covalent (bonds) 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 = mark rigid / hard structure no free electrons po conduct of heat Page 35

36 giant covalent structure = 2 marks max 3 if ionic / metallic bonding mentioned igne electrostatic igne molecules / intermolecular fces [4] M30. (a) nanoparticles / they are small(er) accept 00 nm a few atoms in size so can easily pass through pes / skin / cell / membranes / arteries / veins / capillaries / into blood stream owtte must be a comparative statement can be inferred from smaller particles allow absbed f pass through (b) any one from: may be toxic (to cells / specific cells) allow may harm / damage / kill cells / gans / tissues may cause cancer to ensure safety reduce risk risk of litigation allow may cause allergies / side effects igne harmful / dangerous unqualified eg harmful to body / people nanoparticles may have different properties to see if they pass into the body (c) any two sensible ideas from eg: testing is expensive testing costs money allow it costs money igne litigation testing is time consuming Page 36

37 don t see any reason to test since nmal sized particles (of titanium oxide) do not cause harm accept nmal 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 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 2 [5] Page 37