Structure and Bonding

Transcription

1 Structure and Bonding Mark Scheme Level Subject Exam Board Unit Topic Difficulty Level Booklet GCSE Chemistry AQA C2 Structure and Bonding Bronze Level Mark Scheme Time Allowed: 309 minutes Score: /309 Percentage: /00 Page

2 M.(a) sodium loses (electron) sharing / covalent / metallic = max 2 chlorine gains (electron) or an (electron) (i) Have no overall electric charge Should iodine be added to salt? reason any one from: cannot be done by experiment accept difficult to get / not enough evidence based on opinion / view allow must be done by survey ethical or economic issue. (i) nitric (acid) an alkali indicator accept any named acid base indicator (d) (i) Crystallisation fertiliser allow to help crops grow Page 2

3 any one from: pressure allow concentration temperature ignore heat catalyst. [2] M2.(a) A compound lead nitrate in either order potassium iodide filter paper is missing so solid will go through funnel (d) (i) percentage yield any one from: some product lost reaction may not go to completion unexpected reaction impure reactants. allow insufficient reactant [7] M3.(a) any one from: protection / improve lifespan improve appearance. Page 3

4 (i) Bleach (iv) (v) Hydrogen is less reactive than sodium bonding pair of electrons 6 unbonded electrons on Cl accept dot, cross or e or or any combination Covalent Hydrogen chloride has a low boiling point. Hydrogen chloride is made of simple molecules. (i) oxygen accept carbon dioxide aluminium ions are positive so are attracted (to the negative electrode) allow opposites attract Reduction (iv) slide allow move (d) (i) C strong covalent bonds [4] Page 4

5 M4.(a) (i) 4 isotope (very) small accept smaller / tiny / (very) little (i) C NH 3 (i) nitric (acid) (iv) indicator crystallisation or evaporation allow by heating or cooling or leave (on windowsill) do not accept freezing any one from: grass grows faster grass grows taller or thicker allow grass grows better / greener (d) potassium (atom) loses (an electron) reference to incorrect bonding or particle = max 3 chlorine (atom) gains (an electron) ignore references to full outer shells (electron) electron [3] M5.(a) proton ignore ± Page 5

6 electron very small owtte allow zero allow values from / 800 to / 2000 or (i) Isotopes (d) (i) compound H-O-H covalent (iv) sharing [0] Page 6

7 M6.(a) exothermic Should people use kelp instead of oil as an energy source? Will kelp be more popular than coal in the next 0 years? (i) any four from: If atom or ion omitted = max 3 sharing / covalent / metallic = max 3 ignore reference to full outer shells potassium (atom) loses (an electron) and iodine (atom) gains (an electron) electron iodide (ion) has negative charge allow iodine ion potassium (ion) has positive charge electrostatic attraction or ionic bonding accept stable (structure) or noble gas (structure) 4 because a solid is formed (from two aqueous solutions) filtering or centrifuging or decanting [9] Page 7

8 M7.(a) (i) nucleus neutron electron (i) 2 24 any four from: sharing / covalent / metallic = max 3 magnesium (atom) reacts with two iodine (atoms) magnesium (atom) loses electrons 2 electrons (from each atom) Iodine (atom) gains electron(s) electron or an electron (to each atom) iodide ion formed allow iodine ion iodide has negative charge / is a negative ion / particle allow iodineignore I 2 magnesium ion formed magnesium has positive charge oppositely charged ions attract a giant structure / lattice is formed allow mark for unqualified reference to ion formation or Page 8

9 ionic bonding 4 [9] M8.(a) / one (i) protons neutrons 7 (i) losing a positive electrostatic (d) high melting points strong bonds Page 9

10 (e) (i) 58.5 mole (f) very small (particles) or ignore tiny / small / smaller / microscopic etc. -00nm in size or (particle with a) few hundred atoms [2] M9. (a) (i) C C or D A covalent layers can slide / move over each other accept are weakly bonded (owtte) allow no bonds between layers Page 0

11 ignore slip / rub [6] M0. (a) oxygen and water both needed for mark allow hydrogen oxide for water in any order ignore formulae (i) best fit line, omitting point at 0s straight line drawn through all correct points circle around point at 0 s allow any indication 7.5 allow ecf from candidate s line (iv) increases (with time) accept goes from 0 to 2.5 (i) higher more concentrated Page

12 (d) (i) share covalent simple molecules (e) Water has a boiling point of 00 C Water has a melting point lower than room temperature [2] M. (a) hundred (i) electron(s) Page 2

13 three (d) changes rate of reaction accept lowers activation energy or speeds up / slows down reaction accept reduces costs (e) (i) melt crosslinking allow answers on diagram or (covalent) bonds between polymers / chains allow bonds between layers do not allow intermolecular [8] M2. (a) (i) cryolite lower the melting point of the aluminium oxide (i) opposite charges or oxide ions are negative Page 3

14 attract carbon reacts with oxygen or forms carbon dioxide accept burns Structure mark: either Al (atoms) in layers / rows accept Al (atoms) all the same size allow Al (atoms) in lines or alloy (atoms) not in layers / rows accept different sizes of atoms in alloy allow alloy (atoms) not in lines Sliding mark: either so (Al layers) can slide or so (alloy) layers cannot slide [8] M3. (a) carbon each atom is joined to four other atoms Page 4

15 It has a giant structure very small [4] M4. (a) (i) hydrochloric insoluble filtration crystallisation any four from: any reference to incorrect bonding = max 3 calcium atom reacts with 2 chlorine atoms calcium atoms lose electrons accept calcium ion is formed lose two electrons accept calcium has a 2+ charge / calcium ion has a 2+ charge allow Ca 2+ Page 5

16 chlorine atoms gain electrons accept chloride ion formed gain one electron accept chlorine / chloride has a negative charge / is a negative ion/ is a negative particle allow Cl if no other marks awarded allow ionic bonding or complete outer shell for mark 4 [8] M5. (a) any two from assume it = methanol allow converse for water shorter / quicker soaking time allow it is quicker takes less time / quicker to dry or faster evaporation dissolves quicker / better in methanol 2 (i) CH 4O covalent it is made of small molecules [5] Page 6

17 M6. (a) diagram A the atoms can slide over each other. the atoms are in layers (i) sulfuric bubbles are produced the magnesium disappears crystallisation [7] M7. (a) high melting point not flammable (i) all Page 7

18 two covalent (iv) very strong [6] M8. (a) carbon layers have weak forces / attractions / bonds between them or are only held together weakly second mark must be linked to layers or can slide over each other or separate () covalent [4] Page 8

19 M9. (a) gives out / releases / transfers to surroundings heat / energy ignore light / burns ignore the wire gets hot activation energy (aluminium +) oxygen ( ) aluminium oxide accept correct formulae (d) C (e) (i) a negative loses gains two [8] M20. the atoms are in layers Page 9

20 the atoms can slide over each other [2] M2. (a) the diameter of the tube is very small (i) three covalent bonds [4] M22. (a) (i) 48 3 heat / energy given out / transfers to surroundings Page 20

21 the mark for given out / transfers to cannot be awarded without heat / energy allow given off it has a low boiling point it is made of small molecules [6] M23. (a) (i) mix (owtte) accept to allow more collisions / helps particles to collide (owtte) idea of more efficient heat transfer do not allow heat is a catalyst higher and more powder and big concentrated and more electrons Page 2

22 H+ [6] M24. (a) (i) nucleus neutron electron (i) 6 2 (d) (i) CH 4 compound Page 22

23 covalent [9] M25. (a) carbon all covalent (d) four (e) hard [5] M26. (a) (i) precipitation filtration lead nitrate Page 23

24 sodium iodide sharing / covalent / metallic = max 3 any four from: magnesium (atom) reacts with two iodine (atoms) magnesium (atom) loses 2 electrons iodine (atom) gains electron or an electron iodide ion formed allow iodine ion allow iodine ignore I2 iodide has negative charge / is a negative ion / particle magnesium ion formed magnesium has positive charge oppositely charged ions attract a giant structure / lattice is formed if reference to ions being formed is made unqualified, allow mark 4 [8] M27. (a) metals Page 24

25 copper atoms are arranged in layers copper atoms can slide over each other. the layers of atoms are distorted in bronze [4] M28. (a) (i) all (iv) four covalent hard carbon dioxide accept carbon monoxide accept CO 2 or CO [5] M29. (a) 4 Page 25

26 A it is alkaline accept alkali / basic / base (d) (i) salt nitric fertiliser (e) because energy is taken in (from the surroundings) second mark must be linked to energy [8] M30. (a) because nano-sized particles are smaller than normal sized particles may cause harm when they are inside the body [2] Page 26

27 M3. (a) (i) element compound an / one electron from the sodium atom is lost / transferred to form a sodium ion (i) 8 electrons drawn on outer energy level / shell because oppositely charged ions attract each other or because chloride ions are negative and sodium ions are positive [6] M32. (a) C 3H 8 capital letters for symbols numbers must be halfway or lower down the element symbol allow H 8C 3 do not allow 3:8 or C 3 and H 8 (i) electron covalent Page 27

28 low and small both for mark [4] M33. (a) reduce wear of metal ie don t get damaged or other sensible answer or stop / reduce friction accept stop metal heating up accept move more smoothly ignore make it slippery / rub more smoothly or prevent seizing accept can move freely (i) carbon layers (of atoms) can slide / slip over each other allow slip off or weak forces of attraction / weak bonds (between layers) allow no bonds accept there are weak forces of attraction for mark even when there is no reference to layers accept atoms slide over each other (for mark) an answer which only states there are weak bonds would gain 0 mark when there is no reference to layers weak covalent bonds = 0 marks Page 28

29 [4] M34. (a) (i) increase high melting point (i) decreases increases it gives the particles more energy it makes the particles move faster [6] M35. (a) covalent (i) liquid fluorine accept F / F 2 do not accept fluoride Page 29

30 (i) should fluoride ions be added to drinking water? any one from: not enough reliable/valid evidence may be other factors involved it is an opinion / choice / belief / ethics issue it can t be scientifically investigated allow can t do an experiment ignore test mark independently of (i) [5] M36. (a) any two from: conducts electricity soft slippery high melting point ignore hardwearing / does not stick apply list principle 2 (i) three covalent it is made of layers of atoms [5] Page 30

31 M37. (a) (i) gives out a large amount of energy only water produced / product is non polluting (owtte) allow it does not harm the environment does not explode / burst into flames owtte ignore will not react hydrogen absorbed and released much faster allow more efficient allow can store a larger amount (i) B a lithium atom loses an electron C reversible (d) (i) much smaller surface area [0] Page 3

32 M38. (a) CH 4 4 should be below halfway up H / tail of 4 below the dotted line molecule covalent [3] M39. (a) all three lines correct gains 2 marks one or two correct gains mark if there are more than 3 lines then lose mark for each extra line 2 (i) covalent (iv) (v) four hard three soft carbon accept C Page 32

33 [8] M40. (a) gives out (heat) D L (d) magnesium chloride [4] M4. high giant four allow covalent covalent [4] M42. (a) (i) Page 33

34 all three correct 2 marks one correct mark 2 4 A [4] M43. (a) (i) small or few atoms thick or size in the range 00 nanometres owtte sensible idea of passing through smaller gaps owtte eg can pass through skin / pores / cells or more easily absorbed any two from: good at absorbing UV light / radiation spread more easily cover better save money / use less transparent less chance of getting skin cancer or stops skin cancer ignore more effective alone 2 Page 34

35 toxic to (cells / specific cells) allow harm / damage / kill or cause cancer [5] M44. (a) Cu Fe Zn one significant use for each metal do not credit vague answers such as in experiments and the like do not credit the same use more than once copper examples: do not credit diet supplement coins or coinage (metal) or make alloys or bronze or brass conducting electricity or (electrical) wiring or motors or cables (domestic) (water) pipes heat exchangers roofing steam pipes stills or cooking utensils accept any specified still e.g. whisky still bracelets or rings Page 35

36 iron or steel answers examples: do not credit diet supplement * access-hole covers (sometimes known as manhole covers) * catalyst (in the production of ammonia) * manufacture of steel(s) or in the basic oxygen process * named vehicle or transport or machinery or railings any other uses for iron and steel can be credited provided that the use is clear so, for example, bridges and railway lines would be creditworthy but do not credit buildings and transport which are too vague zinc examples: do not credit diet supplement * brass manufacture * die castings * rust prevention * to galvanise (iron or steel) or (as a) protective coating * battery casing any four general properties of do not credit hard or strong or tough or magnetic are not brittle accept can be bent (into shape) or flexible can be hammered (into shape) accept are malleable can be stretched (into shape) accept are ductile (good) conductors of heat accept just (good) conductor once only (good) conductors of electricity Page 36

37 high boiling points high density or heavy or dense high melting points ringing sound when struck accept sonorous solids (at room temperature) accept shiny (when polished) or silvery 4 (d) any one of do not credit electron references * (good) conductor (of electricity) when molten or liquid accept dissolves in water or crystalline * (good) conductor (of electricity) when in aqueous solution accept (good) conductor (of electricity) when dissolved in water * high melting point or high boiling point do not credit just solid (e) (i) electron from A to B both parts required different numbers of protons accept different atomic numbers do not credit references to neutrons [3] M45. (i) two or 2 magnesium and chloride Page 37

38 either order not positive / negative do not credit chlorine accept Mg++ and Cldo not credit just Mg and Cl accept cation(s) and anion(s) 2 (iv) electrons accept charges (v) any three from (is a) giant structure/lattice structure crystalline / hard accept just 'crystals(s) high melting point / solid high boiling point conductor (of electricity) when dissolved in water or conductor (of electricity) when ions are free to move conductor (of electricity) when molten soluble in water 3 [7] Page 38