AS Paper 1 and 2 Amount of Substance MARK SCHEME

Transcription

1 AS Paper and 2 Amount of Substance MARK SCHEME South Axholme School M.A [] M2.D [] M3.B [] M4.D [] M5.D [] M6.B [] M7.C [] M8.C [] M9.C [] Page

2 M0.B [] M.A [] M2.A [] M3.B [] M4.A [] M5.C [] M6.C [] M7.A [] M8.B [] Page 2

3 M9.B [] M20.A [] M2.B [] M22.D [] M23.D [] M24.B [] M25.D [] M26.A [] M27.B [] Page 3

4 M28.A South Axholme School [] M29.A [] M30.D [] M3.C [] M32.D [] M33.B [] M34.C [] M35.C [] M. (a) Electronegativity increases Proton number increases (increase in nuclear charge) Page 4

5 Same number of electron shells/levels Or same radius or Shielding of outer electrons remains the same South Axholme School Attraction of bond pair to nucleus increases Allow electrons in bond instead of bond pair (b) Big difference in electronegativity leads to ionic bonding, smaller covalent Lose a mark if formula incorrect Sodium oxide ionic lattice Strong forces of attraction between ions P 4O 0 covalent molecular Must have covalent and molecular (or molecules) Weak (intermolecular) forces between molecules Or weak vdw, or weak dipole dipole between molecules melting point Na 2O greater than for P 4O 0 Or argument relating mpt to strength of forces (c) Moles NaOH = = M moles of NaOH correct Moles of H 3PO 4 = /3 moles of NaOH (= ) M2 is for /3 Moles of P in l = = M3 is for factor of,000,000 Moles of P 4O 0 = /4 M4 is for factor of /4 (or /2 if P 2O 5) Mass of P 4O 0 = /4 284 = g = 25 kg (Or if P 2O /2 42) M5 is for multiplying moles by M r with correct units allow conseq on incorrect M4 (allow ) Page 5

6 [5] M2. moles NaOH used = vol / 000 conc () = 2.7 (if uses 25 here only scores first of first 4 marks)/ = () (consider as an arithmetic error loses mark) (range to ) moles HCl in 25 cm 3 = () (or mol HCl reacts with mol NaOH) moles of HCl in 250 cm 3 = () moles ZCl 4 = / 4 = () (or or mark is for / 4) M r = mass / no. Moles () (method mark also.304 / ) = 24.7 () (or gives 27) (allow 24 to 25) A r = = 72.7 () (27 gives 75, 42 is ) Therefore element is Germanium () (allow conseq correct from A r) (75 gives As) If not / 4 C.E. from there on but can score 2 independent marks for (mass / moles / method and identity of element) (for candidates who use m v = m 2v 2 and calculate [HCl] = allow st 3 marks if 25 and 2.7 wrong way round only award /3) [9] M3. (a) Proton: mass, charge + () Neutron: mass, charge 0 () Electron mass /840, charge - () Allow mass = 0, or negligible, or /800 to /2000 Isotopes have the same number of protons () OR atomic number different number of neutrons () Page 6

7 Isotopes have the same electronic configuration () OR same number of electrons Chemical properties depend on electrons () South Axholme School 7 (b) 2 () OR 2 or in words Spectrum gives (relative) abundance () OR % or amount And m/z () Multiply m/z by relative abundance for each isotope () Allow instead of m/z mass no, A r or actual value from example Sum these values () Divide by the sum of the relative abundances () only award this mark if previous 2 given Max 2 if e.g. has only 2 isotopes 7 [4] M4. (a) L = () or must show working = () Ignore wrong units NB answer only scores 2 (b) equal () Or same or : Page 7

8 (c) PV = nrt (or n = ) () = () =.39 () Allow.390 to.395 ignore units even if incorrect answer =.4 loses last mark 3 (d) = 2.93 () mol.dm 3 () OR M, mol/dm 3, mol.l allow to 2.93 Note unit mark tied to current answer but allow unit mark if answer = 2.9 or 3 2 (e) (i) moles H 2SO 4 =.24 = () If use m v = m 2v 2 scores 3 if answer is correct otherwise zero moles NH 3 in 30.8 cm 3 = = () Mark is for 2 CE if 2 not used moles of NH 3 in dm 3 = = 2.0 () (mol dm 3 ) Allow 2.00 to 2.05 No units OK, wrong units lose last mark (ii) moles (NH 4) 2SO 4 = moles H 2SO 4 = 0.30 () Allow consequential wrong moles in part (i) if clear H 2SO 4=(NH 4)SO 4 Wrong formula for (NH 4) 2SO 4 CE=0 M r (NH 4) 2SO 4 = 32. () Allow (32) mass = moles M r = = 4.0 () Page 8

9 if moles of (NH 4) 2SO 4 not clear CE (g) wrong unit loses mark Allow South Axholme School 6 (f) Mg 3N 2 + 6H 2O 3Mg(OH) 2 + 2NH 3 Formulae () Balanced equation () 2 [6] M5. (a) (i) Number of moles of O 2 at equilibrium: = 0.22 () Number of moles of NO at equilibrium: 0.44 () OR 2 mol of oxygen 3 (ii) Original number of moles of NO 2: = 0.46(3) () Number of moles of NO 2 at equilibrium: 0.46(3) 0.44 = 0.02(3) () OR conseq on mol NO above (b) Expression for K C: K C = () Calculation: K C = = 7.0(0) mol dm 3 () () () If mol NO 2 = 0.02; K C = 9.26 (9.3) or conseq on values from (a) If vol missed, score only K C and units If K C wrong: max 2 for correct use of vol and conseq units If K C wrong and no vol: max for conseq units Page 9 3

10 (c) pv = nrt () South Axholme School T = = () for using as V T = 669 K () 4 (d) Yield of oxygen: increased () Value of K c: no effect () 2 [3] M6. (a) (i) Molecule/compound/consists/composed/made up of hydrogen and carbon only () (ii) C nh 2n+2 () (iii) C 6H 4 only () Do not credit structures alone or in addition. 3 (b) Chemically similar / react in same way / same chemistry Differ by CH 2 gradation in physical properties OR specified trend e.g. b.p. same functional group Any 2, 2 marks + Not same molecular formula 2 (c) (i) Same molecular formula () NOT same Mr different structural formula / structures () (or atoms arranged in different way) NOT different spatial arrangements Only credit M2 if M correct Page 0

11 (ii) 2-methylpentane () 2,2-dimethylbutane () South Axholme School (iii) OR correct condensed / structural formula Penalise sticks once Penalise absence of vertical bonds once penalise badly drawn bonds once (vertical between H atoms) 6 (d) (i) M % by mass of H = 7.7(0)% () M2 mol H = 7.70 / = 7.70 mol C = 92.3 / 2 = 7.69 () M3 (ratio : ) CH Credit variations for M2 e.g. 78 = 6 and = 6 Correct answer = 3 marks (ii) (CH has empirical mass of 3 and = 6 ) C 6H 6 () Correct answer mark 4 [5] M7. (a) Ideal gas equation law () Page

12 (b) Moles of X: n = () = = () 6.5 to , min 2 sig figs If write n = zero here, but can score M r Relative molecular mass of X: M r = () 6.5 to 62.5 = 62 () 4 (c) % oxygen = 5.6 (2) C =38.7 / 2 H = 9.68 / O = 57.6(2) / 6 () = 3.23 = 9.68 = 3.23 : 3: CH 3O () If no % O or if wrong A r used then max Correct empirical formula earns all three marks 3 (d) ( CH 3O) = C 2H 6O 2 () [9] M8. (a) Moles HCl = = () (= 0.537) Concentration = () = 2.5 (mol dm 3 ) () Page 2

13 Conseq on correct min 2 d.p. 2.4 to 2.5 Ignore wrong units A.E. lose one mark 3 (b) (i) = 5.7() 0 3 (mol) () 5.7 to (ii) = (mol) () Conseq (iii) = 38 () Conseq (iv) Relative atomic mass of M: = 78 () = 39 () Identify of M: Potassium or K or K + () Conseq If 78 = M r then M = selenium 6 [9] M9. (a) (i) pv = nrt () (ii) Moles ethanol = n =.36/46 (= mol) () Page 3

14 V = nrt/p = () if V = p/nrt lose M3 and M4 = (m 3 ) () = 899 (900) cm 3 () range = If final answer = award (2 + M); if = dm 3 or if = 92 award (3 + M) Note: If.36 or 46 or 46/.36 used as number of moles (n) then M2 and M4 not available Note: If pressure = 00 then, unless answer = dm 3, deduct M3 and mark consequentially 5 (b) (i) Mg 3N 2 + 6H 2O 3Mg(OH) 2 + 2NH 3 () (ii) Moles NH 3 = (=0.055 mol) () Number of molecules of NH 3 = () [mark conseq] = () [range to ] Conseq (min 2 sig fig) 4 (c) Moles NaCl = 800/58.5 (= 3.68) () Moles of NaHCO 3 = 3.68 () Moles of Na2CO 3 = 3.68/2 = 6.84 () Mass of Na 2CO 3 = = 725 g () [range = ] [450 g (range ) is worth 3 marks] Accept valid calculation method, e.g. reacting masses or calculations via the mass of sodium present. Also, candidates may deduce a direct 2: ratio for NaCl:Na 2CO 3 4 [3] M0. Ideal gas equation: pv = nrt () Page 4

15 Calculation: n = pv/rt = () mark for volume conversion fully correct = (mol) () range to M r = m/n =.304/ = 80. () range min 2 s.f. conseq If V wrong lose M2; p wrong lose M3; inverted lose M3 and M4 [5] M. (a) (i) = (mol) () accept or (ii) = (mol) () accept 0.0 If both (i) and (ii) answers wrong, allow ONE process mark for both correct processes (iii) = (mol) () Not conseq must use figures shown (iv) Moles of MgCO 3 = /2 = (mol) () allow Mass of MgCO 3 = () allow 84 mark conseq on moles MgCO 3 =.25g () accept.3g mark conseq Percentage MgCO 3 =.25/ () mark conseq (check for inversion) = 90% () mark conseq Page 5

16 range = % If % expression inverted, lose M4 and M5 South Axholme School 8 (b) (i) % oxygen = 38.0 () Na = 36.5/23 S = 25.5/32(.) O = 38.0/6 () =.587 = = = 2::3 () If no % of oxygen Max (allow M2 only) If % for Na and S transposed, or atomic numbers used, M only available (ii) Na 2SO 3 + 2HCl 2NaCl + H 2O + SO 2 () allow multiples allow SO H+ H 2O + SO 2 4 [2] M2. (a) (i) Atoms with the same number of protons / proton number () NOT same atomic number with different numbers of neutrons () NOT different mass number / fewer neutrons (ii) Chemical properties depend on the number or amount of (outer) electrons () OR, isotopes have the same electron configuration / same number of e (iii) 23/ () CE = 0 if inverted or multiplied tied to M 3.8(2) 0 23 [2-5 sig figs] () 5 (b) s 2 2s 2 2p 6 3s () accept subscripted figures Page 6

17 (c) Highest energy e / outer e s / last e in (3)d sub-shell () OR d sub-shell being filled / is incomplete OR highest energy sub-shell is (3)d NOT transition element / e configuration ends at 3d Q of L (d) N correct symbol () allow Mass number = 5 AND atomic number = 7 () 2 [9] M3. (a) Mg + 2HCl MgCl 2 + H 2 MgO + 2HCl MgCl 2 + H 2O Allow ionic equations (b) Hydrogen collection Using a gas syringe or measuring cylinder/ graduated vessel over water Allow if shown in a diagram Measurements (i) P (ii) T (iii) V Use ideal gas equation to calculate mol hydrogen or mass/mr Mol H 2 = mol Mg (Mark consequentially to equation) 2 (c) MgCl 2 + 2NaOH Mg(OH) 2 + 2NaCl Species Balanced Allow an ionic equation Page 7

18 Mg(OH) 2 MgO + H 2O South Axholme School (d) Allow 2 significant figures in these calculations and ignore additional figures EITHER Mol MgO obtained stage 2 = mass MgO/MrMgO = 6.4/ 40.(3) = 0.59 Allow 0.6 Allow method mark if formula of magnesium oxide or M r incorrect Moles of Mg = moles of H 2 hence Mol original MgO = mol MgO from stage 2 - mol H 2 = = 0.06 Allow 0. Mark consequentially to moles of magnesium oxide determined above OR Mass MgO formed from Mg = M r MgO {or 40.(3)} () = 2.3 g Allow 2. () Allow method mark if formula of magnesium oxide or Mr incorrect Mass original MgO = total mass MgO - mass formed from Mg () NB = = 4.28 g Allow 4.3 () Mark consequentially mass of magnesium oxide determined above As there is an error in part (d), the mass of sample should have been 6.25 NOT 2.65, award full marks to any candidate who has crossed out their correct first answer. [5] M4. (a) (i) Page 8

19 (ii) (mark conseq on (a)(i)) (iii) (mark conseq on (a)(ii)) (iv) 3.0/ (mark conseq on (a)(iii)) 24 (Do not allow 24 without evidence of appropriate calculation in (a)(iii)) (b) M r(na 2CO 3) = 06 M r (xh 2O) = = 44 (mark conseq on M) x = 8 (mark conseq on M2) (Penalise sf errors once only) 3 (c) (i) PV = nrt (ii) Moles A r = 325/39.9 = 8.5 (accept M r = 40) P = nrt/v = ( )/ = Pa or = kpa Range = Pa to Pa (If equation incorrectly rearranged, M3 & M4 = 0 If n =325, lose M2) (Allow M if gas law in (ii) if not given in (i)) 2 [2] M5. (a) (i) 2Na + 2NH 3 2NaNH 2 + H 2 (or multiples) Page 9

20 (ii) (Missing H penalise once only) [NOT dot-and-cross diagrams] [NOT 90 / 80 angles] (need 2 lp & bent shape) (iii) 07 (iv) More lone pairs on NH 2, than on NH3 Lone pairs repel more than bonding pairs Must be comparison (Mark separately) [NOT repulsion between atoms or between bonds] (b) (i) Simplest ratio of atoms of each element in a compound / substance / species / entity / molecule (ii) Mg N O (0.675) MgN 2O 6 (Mark M first. If any wrong A r used = CE = 0) (Accept Mg(NO 3) 2 for M3 if above working shown) [9] Page 20

21 M6. (a) (i) = (mol) accept / 0.05 (ii) = / (mol) only (iii) (mol) Mark conseq on (ii) (iv) = (mol) Mark conseq on (i) & (iii) (v) ½ = (mol) If used Mark conseq on (iv) (.) or (.) Mark for M r = 2.22 g or.83 g (b) pv = nrt = 8.4() 0 3 (mol) = () = (K) Mark conseq on moles Note Sig. fig. penalty - apply once if single sf given, unless calc works exactly [] Page 2

22 M7.B [] M8.C [] M9. (a) moles HNO 3 = = ( mol); moles Pb(NO 3 ) 2 = ½ = (0.3 mol); M r Pb(NO 3 ) 2 = 33(.2); mass Pb(NO 3 ) 2 = 33.2 x 0.3=43.5 g; (accept ) (M & M2 are process marks. If error in M, or in M2, do not mark M4 consequentially, i.e. do not award M4) (if atomic numbers used in M3, do not award M4) (b) (i) pv = nrt; ; = 3.6 X 0 3 ; (If pressure not converted to Pa, max 2) (If n = used = CE; M2 = M3 = 0) (ii) moles NO 2 = 4/ ; [mark is for use of 4/5] Page 22

23 M r NO 2 = 46; = OR ; South Axholme School massno 2 = l0 3 = 0..33(g) OR (g); (if atomic numbers used, M3 = M4 = 0) [] M20. (a) (i) (free ) radical substitution (both words required for the mark) initiation Cl 2 2Cl (credit correct half arrows, but penalise double headed arrows) first propagation CH 3Cl + Cl CH 2Cl + HCl second propagation CH 2Cl + Cl 2 CH 2Cl 2 + Cl (penalise the absence of dots on radicals once only) (penalise radical dot on Cl of CH 2Cl once only) (ii) CH 3Cl + Cl 2 CH 2Cl 2 + HCl (penalise if any radicals appear in this equation) (b) M: mol C = 0./2.0 and mol Cl = 89.9/35.5 M2: Ratio : 2.53 OR : 3 OR CCl3 M3: 237.0/Mr of CCl 3 = 237.0/8.5 = 2 Therefore C 2Cl 6 (correct answer gains full credit) OR M: /00 and /00 Page 23

24 M2: Ratio 23.9/2.0 : 23/35.5 OR 2 : 6 South Axholme School M3: C 2Cl 6 (correct answer gains full credit) (c) any two from CHBr 3 or CBr 4 or C 2H 2Br 4 (or CHBr 2CHBr 2) or C 2Br 6 (or CBr 3CBr 3) (ignore HBr or H 2) (ignore equations and ignore names when given in addition to formulae) (penalise names alone) 2 [0] M2. (penalty for sig fig error =mark per question) (a) (i) moles KNO 3 =.00/0. = (mol) (ii) pv = nrt or n = pv/rt moles O2 = n = = () () = (mol) (mark answer first check back if wrong) (transcription error lose M3, mark M4 conseq on error) (if untraceable figures used M3=M4=0) (if wrong temp conversion lose M3 conseq M4) (if n = RT/pV CE, lose M3 and M4) 2 (b) (i) simplest/lowest ratio of atoms of each / element/s in a compound / substance / species / entity / molecule (ii) K N O Page 24

25 () () KNO 2 () (M3 tied to M2), (M3 can be transferred from equation if ratio correct but EF not given) (if calc inverted, lose M2 and M3), (if used At N / wrong No for Ar then CE, lose M2 and M3) (if % of O missing, award M2 only) 3 (c) 2KNO 3 2KNO 2 + O 2 or fractions/multiples (accept 2KNO 3 K 2N 2O 4 + O 2) (do NOT accept Y in equation) [0] M22. (penalty for sig fig error = mark per question) (a) neutron: relative mass = relative charge = 0 (not neutral ) electron: relative mass = /800 0/negligible or relative charge = (b) 7 O/O7 mass number (Do not accept 7.0) oxygen symbol O (if oxygen + mass number = 7 ()) (if oxygen + mass number = 7 (0)) (if at N 0 given but 8, treat as con for M2) (if lp on Be, diagram = 0) (ignore bond angles) (not dot and cross diagrams) Page 25

26 (c) South Axholme School 2 QoL Linear () bent / V-shaped / angular () (mark name and shape independently) (accept (distorted) tetrahedral) (if balls instead of symbols, lose M can award M2) (penalise missing Cl once only) (not non-linear ) 2 (d) M r (Mg(NO 3) 2 = 58(.3) (if At N 0 used, lose M and M2) moles Mg(OH) 2 = (conseq on wrong M2) (answer to 3+ s.f.) moles HCl = = or (mol) (process mark) vol HCl = = (cm 3 ) (unless wrong unit) (if candidate used 0.07 or 0.07 lose M2) (just answer with no working, if in range = (4). if, say, 34 then =(2)) (if not 2: ratio, lose M3 and M4) (if work on HCl, CE = 0/4) [2] M23. (a) (i) (free )radical substitution (both words required for the mark) (ii) uv light OR sunlight OR high temperature OR 50 C to 500 C (iii) Propagation (ignore chain, first, second in front of the word Page 26

27 propagation) South Axholme School (iv) Termination CH 2CH 3 + Br CH 3CH 2Br OR 2 CH 2CH 3 C 4H 0 (penalise if radical dot is obviously on CH 3, but not otherwise) (penalise C 2H 5 ) (credit 2Br Br 2) (ignore chain in front of the word termination) (b) (i) Fractional distillation OR fractionation (credit gas liquid chromatography, GLC) (ii) CH 3CH 3 + 6Br 2 C 2Br 6 + 6HBr (credit C 2H 6 for ethane) (c) Correct structure for CF 2BrCF 2Br drawn out (penalise Fl for fluorine) (d) (i) 2 bromo 2 chloro,, trifluoroethane OR bromo chloro 2,2,2 trifluoroethane (insist on all numbers, but do not penalise failure to use alphabet) (accept flourine and cloro in this instance) (ii) 97.4 only (ignore units) (iii) (57/ ) = 28.9% OR 28.88% (credit the correct answer independently in part (d)(iii), even if (d)(ii) is blank or incorrectly calculated, but mark consequential on part (d)(ii), if part (d)(ii) is incorrectly calculated, accepting answers to 3sf or 4sf only) (penalise 29% if it appears alone, but not if it follows a correct answer) (do not insist on the % sign being given) (the percentage sign is not essential here, but penalise the use of units e.g. grams) [] Page 27

28 M24. (a) (i) Avogadro s number/constant of molecules/particles/species / [Not atoms ] Or same number of particles as (there are atoms) [Not molecules] in 2.(00)g of 2 C (ii) Moles O 2 = (= mol) = 29 ( ) [Accept answers via 4 separate mole calculations] = mol [answer to 3 + sf] [Mark conseq on errors in M/M2] () (iii) Moles of nitroglycerine = (= mol) [Mark conseq on their moles of O 2] M r of nitroglycerine = 227 or number string Moles of nitroglycerine = = (g) [answer to 3+ sf] [If string OK but final answer wrong then allow M6 but AE for M7] [Mark conseq on error in M r] [Penalise wrong units] [Penalise sig. fig. errors once only in whole question] (b) pv = nrt or pv = or p = p = = Page 28

29 = or 7980 or 7.98 [ignore s.f.] units = Pa or kpa or MPa (as appropriate) [If error in conversion from Pa, treat as a contradiction of the units mark] [If transfer error, mark conseq but penalise M2] [If data from outside of above used, penalise M2 and M3] [If pv expression incorrectly rearranged, penalise M2 and M3] [if T = 373 K used, penalise M2] [] M25. (a) [Diagrams must be complete and accurate] (b) (i) Attraction /electrostatic forces/bonds/attractions between (positive) ions/lattice and delocalised/free electrons/sea of electrons. [Not metallic bonding] [Not just forces ] 2 (ii) Electrostatic attractions/forces between ions or attractions between (oppositely charged) ions/ Na + & Cl [Not ionic bonding] (iii) (Here) the ionic bonding in NaCl is stronger/requires more energy to break than the metallic bonding in Na QoL Accept bonding/forces of attraction in NaCl is stronger than in Na [If IMF/molecules/van der Waals /dipole dipole mentioned in parts(i) or (ii), then CE = 0 for parts (i) and/or(ii) and CE = 0 for part(iii)] Page 29

30 (c) Comparison: Sodium conducts and sodium chloride does NOT conduct Allow only Na conducts Accept Na conducts, NaCl only conducts when molten [Do not accept sodium conducts better than sodium chloride etc.] Explanation: (Delocalised) electrons flow though the metal Allow e move/carry current/are charge carriers/transfer charge. [Not electrons carry electricity ] [Not NaCl has no free charged particles ] Ions can t move in solid salt (d) Layers can slide over each other idea that ions/atoms/particles move [Not molecules] [Not layers separate] (e) (i) Na Cl O 0.9(39) 0.9(38) 2.8(2) Hence: 3 Accept backwards calculation, i.e. from formula to % composition, and also accept route via M r to 23; 35.5; 48, and then to ::3 [If % values incorrectly copied, allow M only] [If any wrong A rvalues/atomic numbers used = CE = 0] (ii) 3Cl 2 + 6NaOH 5NaCl + NaClO 3 + 3H 2O [2] M26. Page 30

31 Mark Range The marking scheme for this part of the question includes an overall assessment for the Quality of Written Communication (QWC). There are no discrete marks for the assessment of QWC but the candidates QWC in this answer will be one of the criteria used to assign a level and award the marks for this part of the question Descriptor an answer will be expected to meet most of the criteria in the level descriptor 4-5 claims supported by an appropriate range of evidence good use of information or ideas about chemistry, going beyond those given in the question argument well structured with minimal repetition or irrelevant points accurate and clear expression of ideas with only minor errors of grammar, punctuation and spelling 2-3 claims partially supported by evidence good use of information or ideas about chemistry given in the question but limited beyond this the argument shows some attempt at structure the ideas are expressed with reasonable clarity but with a few errors of grammar, punctuation and spelling 0- valid points but not clearly linked to an argument structure limited use of information or ideas about chemistry unstructured errors in spelling, punctuation and grammar or lack of fluency (a) (i) M r of C 6H 5NH 2 = 93 M r of CH 3COCl = 78.5 total M r of reagents = % atom economy = 00 QWC = 00 = 5.0 % Page 3

32 (ii) expected yield = = 7.26 kg % yield = 00 = 74. % (iii) Although yield appears satisfactory (74%) % atom economy is only 5% QWC nearly half of the material produced is waste and must be disposed of QWC (b) (nucleophilic) addition-elimination QWC (2) 4 (c) HNO 3 + 2H 2SO 4 NO H3O+ + 2HSO 4 3 [6] M27. (a) (i) Moles of gas produced = 3 Page 32

33 PV = nrt V = nrt/p = /00000 South Axholme School = m 3 (ii) /298 = m 3 (b) (i) any two from: exhaust gases hot so would boil the solution away solution would splash reaction might be too slow would need continuous supply of solution and/or replacement of products 2 (ii) Commercial advantage could sell chlorine and/or hydrogen environmental disadvantage generation of electricity likely to lead to release of CO 2 (or chlorine toxic) (c) % O = 74% N:O = 26/4:74/6 =.86: 4.63 = :2.5 therefore formula is N 2O 5 (d) 2N 2O 2N 2 + O 2 (e) Proportion of O 2 increased leading to higher T (or more complete combustion) [4] Page 33

34 M28. (a) (i) 0.03; (ii) ; Answer to (i) 2 (iii) = 84.3; Allow answer to (ii) Allow (b) = 24.3; mark for -60 Mg; If 47.6 used the answer is 87.6 () And this is Sr () Allow consequential metal from their calculated A Answer has got to be a metal to score M2 [5] M29. (a) (i) 00; Whole expression Ignore >3 sig figs = 35.37(%) allow %; Page 34

35 Allow 35% Allow 2 marks if correct % South Axholme School (ii) Sell the HCl or sell the other product or sell the acid (formed in the reaction); Need a financial gain (b) (i) = 0.869; One mark for M r = 89.9 allow ;; Ignore units 2 (ii) Accept same value as in (i) (iii) = 69.4; Allow ; Accept answer to (ii) 79.9 (iv) 00; Accept /answer to (iii) = 90.75%; If > 00% lose this mark Accept 90.6 to 92% [8] Page 35

36 M30.(a) Mass of mineral on x-axis; If axes unlabelled use data to decide if mass of mineral is on the x-axis. Sensible continuous scales; Lose this mark if the plotted points do not cover at least 9 squares by 7. Lose this mark if the graph plot goes off the squared paper. The graph does not have to start at the origin. Plots points correctly ± one square; Award this mark if the line is close to your line. Draws a best fit straight line Award this mark if best fit line is consistent with candidate s plotted points. Lose this mark if line is kinked or doubled. (b).48 or.49 or.50 or.5 (g); Accept these answers only Ignore precision of answer. Allow range.48.5 (c) (mol); Accept 0.02, Allow answer without working. (d) (.49 / 0.024) = ; Must divide answer to part (b) by answer to part (c) to score first mark. Allow consequential answer from part (b). Allow answer without working. Ignore precision of answer. Page 36

37 (e) Answer to part (e) close to 20.3; Allow consequential answer from part (d). Allow correct calculation of x (f) x must be a whole number; (g) Good / straight line so results good / reliable; Allow consequential answers from candidate s graph Do not allow so results are accurate. Anomaly at.34 g; Allow anomaly clearly indicated on the graph. (h) Ensure reaction / decomposition goes to completion; Do not allow to make fair test or improve reliability Accept to remove all carbon dioxide and water. (i) (i) Percentage errors too high / errors in weighing too high; Do not allow to make fair test or improve reliability Do not allow errors on its own. (ii) Incomplete decomposition or words to that effect; Do not allow to make fair test or improve reliability Do not allow takes too long or wastes chemicals Do not allow not all of the water removed. (j) / 8 = 2.70 and / 84.3 = 0.723; Allow M r of MgCO 3.H 2O = 38.3 MgCO 3.3H 2O; 54 / % Page 37MgCO 3.3H 2O without working

38 scores mark. South Axholme School (k) Atom economy for Reaction is (40.3 / 84.3) x 00 = 47.8% Maximum mark if no working. Ignore precision of answers. Atom economy for Reaction 2 is (40.3 / 58.3) x 00 = 69.% (l) No gas produced in stomach / won t cause wind; Do not allow gas produced on its own. [9] M3.(a) percentage of oxygen is correct calculation of ratios (C 3.25, H 4.7, O 3.645) clearly relates ratios to formula eg simplifies ratios (C, H.29, O.7) or for H then / 6 = 4.7% etc Notes * correct percentage of oxygen can be stated or shown clearly in a calculation * to score final mark must clearly show how ratios relate to C 6H 8O 7 * allow full credit to candidate who correctly finds percentage of oxygen calculates M r shows percentage of H is 8 divided by M r (b) carbon dioxide / CO 2 (c) (i) suitable reaction vessel eg sealed flask or test-tube with side arm or eg tube in bung suitable collection method eg gas syringe / over water in Page 38

39 measuring eg cylinder South Axholme School Notes * collection vessel must allow measurement of gas * if apparatus would leak lose second mark * ignore heating * can draw tubing as single line * accept 2D or 3D diagrams * do not need labels, and ignore mis-labelling (ii) () mass on x-axis Notes * If axes unlabelled use data to decide that mass is on the x-axis sensible scales Notes * lose this mark if the plotted points do not cover at least half of the paper * lose this mark if the graph plot goes off the squared paper plots points correctly ± one square (2) draws appropriate straight line of best fit, omitting point at.7g / 86 cm 3 Notes * lose this mark if the line deviates towards the point at.7g / 86 cm 3 * candidates does not have to extrapolate the line to the origin to score this mark * when checking for best fit, candidate s line must go through the origin ± one square. Extend candidate s line if necessary (3) 29 ± cm 3 Notes * accept this answer only Page 39

40 (d) CO 2 / gas formed distends stomach / produces wind / increases pressure in stomach South Axholme School (e) molecular formula has to be a simple multiple of the empirical formula so approximate M r value will distinguish between the options or equivalent wording (f) gas escapes before bung inserted any 2 for syringe sticks carbon dioxide soluble in water Notes * do not accept operator error / inaccurate equipment / equipment leaks 2 (g) volume depends on pressure and temperature Notes * do not accept to get a more accurate result or equivalent wording without qualification (h) Tablets could vary between samples or equivalent wording Notes * do not accept to get a more accurate / reliable result or to make a fair test without qualification (i) (i) NaHCO 3 least soluble (ii) exhaust gases passed into mixture of NaCl and NH 3 (j) 2NaHCO 3 Na 2CO 3 + CO 2 + H 2O Page 40

41 Notes * accept multiples South Axholme School (k) 06.0 divided by = 48.8% Notes * ignore precision of answer [22] M32. (a) (i) Average/mean mass of atom (of an element); Average mass of atom 2. Mass /2 atom of 2 C; Mass atom of 2 C. QWC. (ii) Other isotope = 46.0%; 07.9 = ; M2 whole expression. 08.8; Answer 08.8 (3 marks). Answer min d.p.. Same electronic configuration/ same number of electrons (in outer shell)/ both have 47 electrons; Ignore protons and neutrons unless incorrect. Not just electrons determine chemical properties. (b) Ionisation; high energy electrons fired at sample; Allow electron gun /blasted with electrons. Acceleration; Page 4

42 With electric field/accelerating potential/potential difference; Allow by negative plate. Deflection; With electromagnet/ magnet/ magnetic field; M2 dependent on M. M4 dependent on M3. M6 dependent on M5. (c) (Silver) metallic (bonding); Vdw/molecules CE=0. Regular arrangement of same sized particles; + charge in each ion; Ignore multiple positive charges. Candidates do not need to show delocalised electrons. (d) Ionic (bonds); Minimum 4 ions shown in 2D square arrangement placed Correctly; Do not allow multiple charges on ions. Further 3 ions shown correctly in a cubic lattice; Strong (electrostatic) forces/bonds; If vdw/molecules/covalent mentioned CE = 0 for M4 and M5. Between + and ions; Accept between oppositely charged ions. [20] Page 42

43 M33. (a) (i) / ; Penalise < 3sf in (a)(i); Allow (for candidates who have used Mg as 24) South Axholme School (ii) Allow correct answer a(i) 2. (iii) / ; Allow / (iv) moles; Allow range to Allow (a)(iii) 2 (a)(ii) (must be positive). (b) PV = nrt; Allow all capitals/ lower case. V = ; M2 Mark is for all numbers correct. If units in answer are in dm 3 allow this expression with 96 in denominator m 3 / 3.2 dm 3 ; M3 Must have correct units/ allow 3200 cm 3. Allow min 2 sig figs in answer. (c) O = 69.6 (%); 2.7 : 4.35 Use of 7/8 CE then M only. Page 43

44 ( : 2) NO 2 Mark for formula not ratio. If NO 2 and no working shown then allow mark. If 69.6% + NO 2 only = 2. Need to see evidence of M2 working. Allow M2 conseq on the wrong M (ie max ). [0] ## (a) Average/mean mass of () atom(s) (of an element) /2 mass of one atom of 2 C OR If moles and atoms mixes Max = (Average) mass of one mole of atoms /2 mass of one mole of 2 C OR (Weighted) average mass of all the isotopes /2 mass of one atom of 2 C OR Average mass of an atom/isotope compared to C-2 on a scale in which an atom of C-2 has a mass of 2 This expression = 2 marks (b) d block Allow 3d/D Other numbers lose M Ignore transition metals [Ar] 3d 2 4s 2 Can be written in full Allow subscripts 3d 2 and 4s 2 can be in either order 27 Page 44

45 (c) (= 550) (or their abundances) If one graph reading error lose M and allow consequential M2 and M3. If 2 GR errors penalise M and M2 but allow consequential M3 If not 7 or their abundances lose M2 and M3 = = 3 marks provided working shown. Zr/Zirconium M4 -allow nearest consequential element from M3 accept Zr in any circumstance (d) High energy electrons/bombarded or hit with electrons accept electron gun knocks out electron(s) (to form ions) Z + = 90 deflected most If not 90 lose M3 and M4 If charge is wrong on 90 isotope lose M3 only Accept any symbol in place of Z since lowest mass/lowest m/z Allow lightest (e) (ions hit detector and) cause current/(ions) accept electrons/cause electron flow QWC bigger current = more of that isotope/current proportional to abundance Implication that current depends on the number of ions [5] Page 45

46 ## (a) Average/mean mass of () atom(s) (of an element) /2 mass of one atom of 2 C OR If moles and atoms mixes Max = (Average) mass of one mole of atoms /2 mass of one mole of 2 C OR (Weighted) average mass of all the isotopes /2 mass of one atom of 2 C OR Average mass of an atom/isotope compared to C-2 on a scale in which an atom of C-2 has a mass of 2 This expression = 2 marks (b) d block Allow 3d/D Other numbers lose M Ignore transition metals [Ar] 3d 2 4s 2 Can be written in full Allow subscripts 3d 2 and 4s 2 can be in either order 27 (c) (= 550) (or their abundances) If one graph reading error lose M and allow consequential M2 and M3. If 2 GR errors penalise M and M2 but allow consequential M3 If not 7 or their abundances lose M2 and M3 Page 46

47 = = 3 marks provided working shown. South Axholme School Zr/Zirconium M4 -allow nearest consequential element from M3 accept Zr in any circumstance (d) High energy electrons/bombarded or hit with electrons accept electron gun knocks out electron(s) (to form ions) Z + = 90 deflected most If not 90 lose M3 and M4 If charge is wrong on 90 isotope lose M3 only Accept any symbol in place of Z since lowest mass/lowest m/z Allow lightest (e) (ions hit detector and) cause current/(ions) accept electrons/cause electron flow QWC bigger current = more of that isotope/current proportional to abundance Implication that current depends on the number of ions [5] Page 47