Markscheme May 2017 Chemistry Standard level Paper 2

Transcription

1 M7/4/CHEMI/SP/ENG/TZ/XX/M Markscheme May 07 Chemistry Standard level Paper pages

2 M7/4/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 M7/4/CHEMI/SP/ENG/TZ/XX/M. a i 3.75 g Accept other valid methods for M. n(ag) «mol» g mol AND g 3.75 g n(o) «mol» 6.00 gmol 6.00 Award [ max] for correct empirical formula if method not shown «/ ratio of Ag to O approximately :, so» AgO. a ii temperature too low heating time too short oxide not decomposed completely heat sample to constant mass «for three or more trials». b A r closer to 07/less than 08 «so more 07 Ag» A r less than the average of (07 09) «so more 07 Ag» Accept not heated strongly enough. If M as per markscheme, M can only be awarded for constant mass technique. Accept "soot deposition" (M) and any suitable way to reduce it (for M). Accept "absorbs moisture from atmosphere" (M) and "cool in dessicator" (M). Award [ max] for reference to impurity AND design improvement. Accept calculations that gives greater than 50% 07 Ag.

4 4 M7/4/CHEMI/SP/ENG/TZ/XX/M c i Flask containing Colour of solution Product formula Do not accept name for the products. Accept Na OH for NaOH. Na O blue NaOH AND P 4 O 0 yellow H 3 PO 4. c ii «molten» Na O has mobile ions/charged particles AND conducts electricity «molten» P 4 O 0 does not have mobile ions/charged particles AND does not conduct electricity/is poor conductor of electricity. d electrons in discrete/specific/certain/different shells/energy levels energy levels converge/get closer together at higher energies energy levels converge with distance from the nucleus Ignore coefficients in front of formula. Do not award marks without concept of mobile charges being present. Award [ max] if type of bonding or electrical conductivity correctly identified in each compound. Do not accept answers based on electrons. Award [ max] if reference made to solution. Accept appropriate diagram for M, M or both. Do not give marks for answers that refer to the lines in the spectrum. 3

5 5 M7/4/CHEMI/SP/ENG/TZ/XX/M. a i Sn (aq) Sn 4 (aq) e Accept equilibrium sign. Accept Sn (aq) e Sn 4 (aq).. a ii Cr O 7 (aq) 4H (aq) 3Sn (aq) Cr 3 (aq) 7H O (l) 3Sn 4 (aq) Accept equilibrium sign.. b i «3.39 g 0.00 g so percentage uncertainty» 0.0 «%» Accept answers given to greater precision, such as 0.05 %.. b ii 3.39 g «[K Cr O 7 ] g mol 0.00 dm» «mol dm 3». b iii n(sn 3mol ) «0.450 mol dm dm 3 mol «[Sn 0.079mol ]».79 «mol dm 3» dm» «mol» Award [] for correct final answer.

6 6 M7/4/CHEMI/SP/ENG/TZ/XX/M 3. a i PCl Cl 3 «K c» PCl 5 3. a ii decrease in temperature Do not accept temperature change. endothermic «reaction» AND «equilibrium» shifts to the left/reactants endothermic «reaction» AND K c decreases endothermic «reaction» AND concentration of PCl 5 increased/concentration of PCl 3 and Cl decreased «equilibrium» shifts in exothermic direction 3. b Lewis structure: Accept H positive in place of endothermic. Accept products instead of PCl 3 and Cl. Penalize missing lone pairs once only between this question and 4(b). Accept any combination of lines, dots or crosses to represent electrons. Molecular geometry: trigonal/triangular pyramidal Do not apply ECF.

7 7 M7/4/CHEMI/SP/ENG/TZ/XX/M 4. a i triple bond in nitrogen «molecule» AND single bond in hydrazine Accept bond enthalpy values from data booklet (58 and 945 kj mol ). triple bond stronger than single bond more shared «pairs of» electrons make bond stronger/attract nuclei more 4. a ii hydrogen bonding «between molecules, dinitrogen tetraoxide does not» 4. a iii N H 4 : AND N O 4 : 4 4. a iv N H 4 AND oxidized/oxidation state increases N H 4 AND loses hydrogen N H 4 AND reduces/removes oxygen from N O 4 4. b Accept N H 4 AND gives electrons «to N O 4». Accept any combination of lines, dots or crosses to represent electrons. Do not penalize missing lone pairs if already done in 3b. Do not accept structure that represents.5 bonds.

8 8 M7/4/CHEMI/SP/ENG/TZ/XX/M 5. a i concentration of acid decreases Accept less frequency/chance/rate/ probability/likelihood of collisions. surface area of magnesium decreases Do not accept just less acid or less magnesium. Do not accept concentrations of reagents decrease. 5. a ii curve starting from origin with steeper gradient AND reaching same maximum volume 5. b «E a(rev) 6 3» 358 «kj» Do not accept c NO (g) H O (l) HNO 3 (aq) HNO (aq) Accept ionised forms of the acids. 4NO (g) H O (l) O (g) 4HNO 3 (aq)

9 9 M7/4/CHEMI/SP/ENG/TZ/XX/M 6. a Initiation: Do not penalize missing electron dot on C C l l Cl Cl radicals if consistent throughout. Accept Cl, HCl and CH 3 Cl without showing bonds. Propagation: Do not accept hydrogen radical, H or 3 Cl CH C l H CH H, but apply ECF to other propagation 4 3 steps. C C l l CH C CH l Cl 6. b hexane AND hex--ene Accept benzene AND hexane AND hex--ene. 6. c 3 3 Accept CH CHCl or CHClCH. Do not accept C H 3 Cl.

10 0 M7/4/CHEMI/SP/ENG/TZ/XX/M 7. a i water/h O Accept hydroxide ion/oh a ii Acid Base HOCl H O AND AND OCl OH 7. b i «0.00 mol dm dm 3» «mol» 7. b ii 0.50 g «M» 04 «g mol» mol 7. b iii « [H ] 0.00» «mol dm 3»

11 M7/4/CHEMI/SP/ENG/TZ/XX/M 8. a i 89. Accept other methods for correct H «kj» manipulation of the three equations. Award [] for correct final answer. «H» 03. «kj» 8. a ii 03. «kj» «kg» 4.8 «kj kg K» T «K» «T» 57. «K» «T final (57..8) C» 79.0«C» / 35.0 «K» If 00.0 kj was used: 00.0 «kj» «kg» 4.8 «kj kg K» T «K» «T» 56.3 «K» Award [] for correct final answer. Units, if specified, must be consistent with the value stated. «T final (56.3.8) C» 78. «C» / 35. «K» 8. b C 6 H 4 (OH) Accept molecular ion. Do not accept C 6 H 4 (OH) (positive charge missing). 8. c «highest m/z» 08 Only accept exactly 08, not values close to this.