Markscheme May 2018 Chemistry Standard level Paper 2

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1 M8/4/CHEMI/SP/ENG/TZ/XX/M Markscheme May 08 Chemistry Standard level Paper 3 pages

2 M8/4/CHEMI/SP/ENG/TZ/XX/M This markscheme is the property of the International Baccalaureate and must not be reproduced or distributed to any other person without the authorization of the IB Global Centre, Cardiff.

3 3 M8/4/CHEMI/SP/ENG/TZ/XX/M. a n(h SO 4 ) « dm mol dm 3» / «mol». b H SO 4 (aq) Mg(OH) (s) MgSO 4 (aq) H O (l) Accept an ionic equation.. c «n(h SO 4 ) n(naoh) ( dm mol dm 3 )» / «mol». d n(h SO 4 ) reacted « » / «mol». e n(mg(oh) ) «n(h SO 4 )» / «mol» m(mg(oh) ) « mol g mol» 0.3 «g» Award [] for correct final answer.. f % Mg(OH) «0.3 g 00» 8.0 «%» Answer must show three significant.4 g figures.

4 4 M8/4/CHEMI/SP/ENG/TZ/XX/M. a M: Accept speed for x-axis label. Accept number of particles, N, frequency or probability «density» for y-axis label. Do not accept potential energy for x-axis label. M: Do not accept a curve that touches the x-axis at high energy. Do not award M if two curves are drawn. 3 both axes correctly labelled correct shape of curve starting at origin E a(catalyst) < E a(without catalyst) on x-axis M3: Ignore any shading under the curve.

5 5 M8/4/CHEMI/SP/ENG/TZ/XX/M. b i. b ii rate decreases curve starting from origin with steeper gradient AND reaching same maximum volume slower reaction «ethanoic acid» partially dissociated/ionized «in solution/water» lower [H ] Accept weak acid or higher ph.

6 6 M8/4/CHEMI/SP/ENG/TZ/XX/M. c «ph» converts «wide range of [H ]» into simple «log» scale/numbers «ph» avoids need for exponential/scientific notation «ph» converts small numbers into values «typically» between 0/ and 4 «ph» allows easy comparison of values of [H + ]. d «species» do not differ by a «single» proton/h + conjugate base of H 3 PO 4 is H PO 4 «not HPO 4» conjugate acid of HPO - 4 is H PO 4 «not H 3 PO 4» Accept uses values between 0/ and 4. Do not accept easier to use. Do not accept easier for calculations. Do not accept hydrogen/h for H + /proton.

7 7 M8/4/CHEMI/SP/ENG/TZ/XX/M 3. a i 3. a ii 4 levels showing convergence at higher energy arrows (pointing down) from n 3 to n AND n 4 to n

8 8 M8/4/CHEMI/SP/ENG/TZ/XX/M 3. b i same number of shells/«outer» energy level/shielding AND nuclear charge/number of protons/z eff increases «causing a stronger pull on the outer electrons» 3. b ii K + 9 protons AND Cl 7 protons K + has «two» more protons same number of electrons/isoelectronic «thus pulled closer together» 3. c i 3. c ii Anode (positive electrode): Cu(s) Cu (aq) e Cathode (negative electrode): Cu (aq) e Cu (s) Accept Cu(s) e - Cu + (aq). Accept for Award [ max] if the equations are at the wrong electrodes. 3. c iii «external» circuit/wire AND from positive/anode to negative/cathode electrode Accept through power supply/battery instead of circuit.

9 9 M8/4/CHEMI/SP/ENG/TZ/XX/M 4. a bonds broken: 4(C H) (H O) / 4(44) (463) / 58 «kj» bonds made: 3(H H) C O / 3(436) 077 / 385 «kj» » 97 «kj» H «BE BE (bonds broken) (bonds made) 4. b i for any element 0 «by definition» no energy required to form an element «in its stable form» from itself 4. b ii H Ö «(products) (reactants) 0 [ 74.0 ( 4)]» 05 «kj» 4. b iii «bond enthalpies» averaged values «over similar compounds» «bond enthalpies» are not specific to these compounds Award [3] for correct final answer. Award [ max] for 97 «kj» a Q: non-equilibrium concentrations AND K c : equilibrium concentrations Q: «measured» at any time AND K c : «measured» at equilibrium 5. b [SO ].00 3 «Q SO O » reverse reaction favoured/reaction proceeds to the left AND Q > K c /0.500 > 0.8 Do not award M without M.

10 0 M8/4/CHEMI/SP/ENG/TZ/XX/M 6. a i polar bonds «between H and group 6 element» difference in electronegativities «between H and group 6 element» uneven distribution of charge/electron cloud non-linear/bent/v-shaped/angular shape «due to lone pairs» polar bonds/dipoles do not cancel out 6. a ii number of electrons increases London/dispersion/instantaneous induced dipole-induced dipole forces increase M: Do not accept net/overall dipole moment without further explanation. Accept non-symmetrical «shape/distribution of charge». M: Accept M r /A r increases or molecules become larger in size/mass/surface area. 6. b Electron domain geometry: tetrahedral Molecular geometry: bent/v-shaped/angular Both marks can be awarded for clear diagrams. Electron domain geometry requires a 3-D diagram showing the tetrahedral arrangement.

11 M8/4/CHEMI/SP/ENG/TZ/XX/M 7. a Physical evidence: equal C C bond «lengths/strengths» regular hexagon «all» C C have bond order of.5 «all» C C intermediate between single and double bonds M: Accept all C C C bond angles are equal. Chemical evidence: undergoes substitution reaction «more readily than addition» does not discolour/react with bromine water substitution forms only one isomer for,-disubstitution «presence of alternate double bonds would form two isomers» more stable than expected «compared to hypothetical molecule cyclohexa-,3,5-triene» enthalpy change of hydrogenation/combustion is less exothermic than predicted «for cyclohexa-,3,5-triene»

12 M8/4/CHEMI/SP/ENG/TZ/XX/M 7. b i 3CH 3 CH CH OH (l) Cr O 7 (aq) 8H (aq) 3CH 3 CH CHO (aq) Cr 3 (aq) 7H O (l) correct reactants and products balanced equation 7. b ii Aldehyde: by distillation «removed from reaction mixture as soon as formed» Accept clear diagrams or descriptions of the processes. 7. c i Carboxylic acid: «heat mixture under» reflux «to achieve complete oxidation to COOH» 36 «48 4 6» C 8 H 8 O 7. c ii A: C H «in alkanes, alkenes, arenes» AND B: C=O «in aldehydes, ketones, carboxylic acids and esters»

13 3 M8/4/CHEMI/SP/ENG/TZ/XX/M 7. c iii Any two of: Do not penalize use of Kekule structures for the phenyl group. C 6 H 5 COOCH 3 Accept the following structures: CH 3 COOC 6 H 5 HCOOCH C 6 H 5 CH 3 O H O Award [ max] for two correct aliphatic/linear esters with the molecular formula C 8 H 8 O. 7. c iv C 6 H 5 COOCH 3 «signal at 4 ppm ( range in data table) due to alkyl group on ester»

Markscheme November 2017 Chemistry Higher level Paper 2

Markscheme November 2017 Chemistry Higher level Paper 2 N7/4/CHEMI/HP/ENG/TZ0/XX/M Markscheme November 07 Chemistry Higher level Paper 9 pages N7/4/CHEMI/HP/ENG/TZ0/XX/M This markscheme is the property of the International Baccalaureate and must not be reproduced