Markscheme November 2015 Chemistry Higher level Paper 2

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1 N15/4/EMI/P2/ENG/TZ0/XX/M Markscheme November 2015 hemistry igher level Paper 2 16 pages

2 2 N15/4/EMI/P2/ENG/TZ0/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 Assessment entre.

3 3 N15/4/EMI/P2/ENG/TZ0/XX/M Subject Details: hemistry L Paper 2 Markscheme Mark Allocation andidates are required to answer ALL questions in Section A [40 marks] and TWO question in Section B [2 x 25 marks]. Maximum total = [90 marks]. 1. A markscheme often has more marking points than the total allows. This is intentional. 2. Each marking point has a separate line and the end is shown by means of a semicolon (;). 3. An alternative answer or wording is indicated in the markscheme by a slash (/). Either wording can be accepted. 4. Words in brackets ( ) in the markscheme are not necessary to gain the mark. 5. Words that are underlined are essential for the mark. 6. The order of marking points does not have to be as in the markscheme, unless stated otherwise.

4 4 N15/4/EMI/P2/ENG/TZ0/XX/M Section A 1. IO3 to I 2 : V/ 5 to 0; I to I 2 : I/ 1 to 0; Accept change in oxidation number 5 and 1. Penalize incorrect notation such as 5 or 5 once only. Oxidizing agent: IO3 /iodate and Reducing agent: I /iodide; / (mol of KIO3); ( ) 0.107(g) ; Award for the correct final answer. (c) 1.4 (%); Accept 1 (%). systematic; dilute the orange juice; Accept other valid suggestions, eg. compare with a standard (showing colour at equivalence) / look at mixture through a yellow filter / add more starch (for a sharper colour change) / filter orange juice (through charcoal). Do not accept repeat titrations or alternative indicator. (d) (mol) ; IO3 : 368O6 / 1:3 mole ratio; ( mol 3 ) (mol) ; Award for the correct final answer. Award [1 max] for 4.80 x 10 6 (mol) obtained from reversed ratio, 3:1. (e) (f) ( ) (g) ; Accept Mr 176 and mass (g). Ea / 1233 (K) ; R Accept value from 1200 to 1260 (K). gradient Ea ( ) Jmol 1 / 10.2kJ mol 1 correct Ea value; correct units; Allow value in range kj mol 1. Answer must be given to three significant figures. Award for correct final answer and units. Accept J or kj instead of J mol 1 or kj mol 1.

5 5 2. N15/4/EMI/P2/ENG/TZ0/XX/M (u) 1s2 2s2 2p6 3s2 3p6 4s13d10 / 1s2 2s2 2p6 3s2 3p6 3d10 4s1 ; Do not accept [Ar] 4s13d10. (u2 ) 1s2 2s2 2p6 3s2 3p6 3d9 ; Do not accept [Ar] (c) d9. (N3) Lewis base and (u2 ) Lewis acid; N3/ligand donates an electron pair (to u2 ) / u2 accepts an electron pair (from N3); forming coordinate/dative (covalent) bond; Accept coordination bond. Do not accept just covalent bond. d orbitals are split (into two sets of different energies); (frequency/wavelength of visible) light absorbed by electrons moving between d levels/orbitals; colour due to remaining frequencies/complementary colour transmitted; u2 has unpaired electrons/partially filled d sub-level / Zn2 has filled d sub-level; Accept d-d transitions possible between orbitals for M2. [4] 38 (g) 5O2 (g) 3O2 (g) 42O(g) ; Ignore state symbols. bonds broken: 2( )/694 8( )/3304 5(O O)/2490 / 6488 (kj); bonds made: 6( O)/4476 8(O )/3712 / 8188 (kj); ( ) 1700 (kj mol 1); Ignore signs in M1 and M2. Award for the correct final answer. Award for 1700 (kj mol 1). Accept values from 2016 data booklet to give 6494 (kj) for M1, 8528 (kj) for M2, and 2034 (kj) for M3. OO (2 )4 OO ; Accept OO(2)4OO but not OO(2)4OO or OO(2)4OO. 2N(2 )6 N2 ; Accept N2(2)6N2 but not 2N(2)62N or N2(2)62N. Accept full or condensed structural formulas. Type: condensation (polymerization); Structural feature: two functional groups on each monomer; Accept ON ; Accept this group if correctly identified as part of polymer chain. water/2o; (c)

6 6 5. N15/4/EMI/P2/ENG/TZ0/XX/M ability of an atom to attract (a pair of) electrons in a covalent bond/molecule / ability of an atom to attract a shared pair of electrons; Do not accept element/nucleus instead of atom. do not form bonds/compounds / do not share electrons / have (full/stable) octet / have full/stable outer shell; Accept (chemically) inert / do not react / stable electron arrangements/ configurations. (Li s) atomic/ionic radius increases; force of attraction between metal ions and delocalized electrons decreases; Accept metallic bonding gets weaker. (F I ) London/dispersion/instantaneous induced dipole-induced dipole forces increase; Accept vdw/van der Waals' forces for London/dispersion forces. with increasing number of electrons/molar mass/surface area/size of electron cloud; Do not accept with increasing size or with increasing mass only. (c) Na has one less energy level/shell compared to Na atom / Na has 2 energy levels/shells compared to 3 in Na atom; (compared to Na atom) effective nuclear charge greater in Na (so valence electrons attracted more strongly to nucleus) / (compared to Na atom) more protons than electrons in Na (so valence electrons attracted more strongly to nucleus); [3 max] [1 max]

7 7 N15/4/EMI/P2/ENG/TZ0/XX/M Section B 6. possible to get iron and 3:1 ratio of the two equations; The ratio may be shown in combining the equations/calculating overall G/ 29 (kj). possible to get iron and resultant G is negative/ 29 (kj); Possible to get iron needs only to be stated once. Do not accept possible to get iron without any reason. Do not accept it is not possible to get iron because G is positive. G Ö [ ] [ 742] ; G Ö 820(kJ mol 1 ) ; Award for the correct final answer. S G Ö [ (298 ( ))] ; Ö [ (34.8)] [ (28.3)] 23.6 (JK 1 mol 1 ) ; GÖ 818(kJ mol 1 ) / (J mol 1 ) ; Award for the correct final answer. Award [0] if b is repeated here. (c) ybridization NF4 N2 2 N2 4 sp3; sp2; sp3; Do not penalize if it is not superscript. sigma bond: overlapping of orbitals end to end/head on / overlapping of orbitals along internuclear axis; Accept axial overlapping of orbitals. pi bond: side-ways/parallel overlapping of p orbitals (above and below internuclear axis); Accept overlapping of p orbitals above and below the internuclear axis. Accept suitable labelled diagrams.

8 8 N15/4/EMI/P2/ENG/TZ0/XX/M See saw; Octahedral; [4] Accept any combination of lines, dots or crosses to represent electron pairs. Penalize missing lone pairs on fluorine atoms once only. For SF4, lone pair on S required for the mark. Do not allow EF for a wrong Lewis structure. Accept saw horse/distorted tetrahedron instead of see-saw. (d) 323 3O 32O 3OO ;; Award for correct order. Award for 3OO 32O 3O 323 as compounds are not listed in order of increasing boiling point. Award if one error in the order. 323 /London/dispersion/instantaneous induced dipole-induced dipole forces 3O dipole-dipole forces (and London/dispersion forces) 32O -bonding (and dipole-dipole and London/dispersion forces) 3OO -bonding (and dipole-dipole and London/dispersion forces);; Award for all four correct. Award for two or three correct. -bonding strongest / London/dispersion forces weakest / dipole-dipole stronger than London/dispersion / dipole-dipole weaker than -bonding; Accept van der Waals forces for London/dispersion forces. 3OO forms more/stronger -bonds than 32O / 3OO is more polar than 32O; Accept 3OO has more electrons/higher molar mass than 32O. (e) ionization and (bombardment) by high energy/fast moving electrons/electron gun (to form positive ions); acceleration and passing through electric field/potential difference/oppositely charged plates; deflection and passing through magnetic field/electromagnet; Award for naming 3 processes (ionization, acceleration, deflection) in the correct order with incorrect details. [4]

9 9 7. N15/4/EMI/P2/ENG/TZ0/XX/M Increasing the pressure, at constant temperature: decreases; more (gas) molecules/moles on the right / fewer (gas) molecules/moles on the left; Increasing the temperature, at constant pressure: increases; (forward) reaction is endothermic; (iv) equilibrium reached faster; no change in the concentration of reactants/products/yield (at equilibrium) / position of equilibrium is not affected; rates of forward and reverse reactions increase (equally); reduces activation energy; no change in Kc; [2 ]3 [O] (K c ) ; [4 ][2O] [4] [3 max] (increasing) temperature and (Kc) increases; Award [0] if both temperature and pressure stated. O (g) 2 O (g) 2 (g) O 2 (g) (1.00 x ) (1.00 x ) x x x2 K c 10.0 / 10.0 (1.00 x ) x / (1.00 x ) ; 2 x (1.00 x ) ; [O] 0.240(moldm 3 ) and [2O] = 0.240(moldm 3 ) and [2 ] 0.760(moldm 3 ) 3 and [O2 ] 0.760(moldm ) ; (c) Order with respect to O2: first (order); Order with respect to NO: second (order); (rate ) k [NO]2 [O2 ] ; / 173 ; mol 2 dm6 s 1 ; 2 1 Accept M s /mol 2 L2 1 s.

10 10 (iv) N15/4/EMI/P2/ENG/TZ0/XX/M NO NO N2O 2 (fast); N2O2 O2 2NO2 (slow); second step is rate determining step; OR NO + O2 O + NO2 (fast); O + NO NO2 (slow); second step is rate determining step; OR NO + O2 NO3 (fast); NO3 + NO 2NO2 (slow); second step is rate determining step; Accept single arrow instead of reversible sign. Accept fast/slow next to the equations. Do not accept the following mechanisms: NO + NO NO2 + N (fast) N + O2 NO2 (slow) OR NO + NO + O2 N2O4 (slow) (d) (e) N2O 4 2NO 2 (fast) Pb Ni Fe Zn;; Award for the correct order. Award for Zn Fe Ni Pb as metals not listed in order of increasing reactivity. Award if one error in the order. Pb2 / lead(ii) (ions); Do not accept Pb/lead. Dilute sodium chloride: 1 1 2O(l ) O2 (g) 2 (aq) 2e / 2O (aq) O2 (g) 2O(l ) 2e ; 2 2 oncentrated sodium chloride: l (aq) 1 l2 (g) e ; 2 Award [1 max] if equations are given the wrong way round. Accept e instead of e. Ignore state symbols and equilibrium sign. Accept correct half-equations balanced with different coefficients.

11 N15/4/EMI/P2/ENG/TZ0/XX/M base I: 7.0; base II: 5.5; base I: strong base and base II: weak base; NaO and KO; Accept LiO. (iv) 3 3 (from the graph: initial p 11, po 3) [O ] 10 (mol dm ) ; / ; x Kb ; Kb OR at half-equivalence point, p 9.0 pka for base II; pkb ; Award M1 and M2 for stating: at half-equivalence point po 5 pkb for base II. Kb ; Accept other valid methods of working. Accept a slightly different value of pkb and so Kb if the student uses the p at the end point, rather than the initial or half-neutralisation values. (v) methyl red; Do not accept bromocresol green (since from table 16 data booklet p range, 3.8 is too low). resists change in p; on addition of small amounts of acid and base; (after mixing) [N3 ] [N4 ] / n N3 n N4 / n mol ; [O ] Kb [base] / po pkb 4.75; [salt] p 9.25; Award [1 max] if no working shown. Accept other valid methods of working. (c) Reaction A: base and accepts a proton/ ; Accept donates a pair of electrons. Reaction B: acid and donates a proton/ ; Award if acid and base identified correctly without a reason. onjugate acid-base pair 1/2 onjugate acid-base pair 2/1 onjugate acid-base pair 1/2 Acid 2O3 O3 3O and and and Base O3 ; O32 ; 2O; [2 max]

12 12 (d) (e) N15/4/EMI/P2/ENG/TZ0/XX/M strong acid: (assumed to be) completely/100% dissociated/ionized and weak acid: partially dissociated/ionized; Similarity: bubbling/effervescence/gas / heat/increase in temperature / solid dissolves; Difference: strong acid more vigorous / faster reaction / greater temperature increase; Accept converse statements for weak acid. 104(: 1) / 10 1:10 5 / 1:10 4 ; Do not accept inverse ratio, 1:104. Na and Mg: basic Al: amphoteric Do not accept amphiprotic. Si to l: acidic Ar: no oxide ;; Award for three or four correct, award for two correct. Award for stating oxides become more acidic towards the right/chlorine or more basic towards the left/sodium. Do not penalize incorrect formulas of oxides. Na2O(s) 2O(l ) 2NaO(aq) / Na2O(s) 2l (aq) 2Nal (aq) 2O(l ) ; Accept a correct equation with any acid or acidic oxide. SO3 (l) 2O(l) 2SO4 (aq) / SO3 (l) 2NaO (aq) Na2SO4 (aq) 2O (l); Accept a correct equation with any metal hydroxide, metal oxide, metal carbonate or metal hydrogen carbonate. Do not accept equation with SO2. Ignore state symbols. Accept ionic equations for M1 and/or M2. 9. RBr (l ) NaO(aq) RO(aq) NaBr (aq) / RBr (l) O (aq) RO(aq) Br (aq) ; Ignore state symbols. ( ) / (mol) ; (molar mass )137 (g mol 1); Accept 138. (iv) ( which corresponds to 49, hence molecular formula) 49Br; Accept correct structural formula of one of the isomers as molecular formula. Do not accept EF from 9a for an impossible molecular formula, such as 410Br.

13 13 (v) N15/4/EMI/P2/ENG/TZ0/XX/M 3222Br and primary; (3)22Br and primary; 3Br23 and secondary; (3)3Br and tertiary; If primary, secondary or tertiary not stated, award for four correct, for three correct and for two correct structural formulas. Penalize missing hydrogens once only. Accept either full or condensed structural formulas. If 511Br was used, accept any correct structural formulas Br and primary; (3)222Br and primary; 32(3)2Br and primary; (3)32Br and primary; 3Br223 and secondary; 32Br23 and secondary; 3Br(3)2 and secondary; 32(3)2Br and tertiary; If primary, secondary or tertiary not stated, award for four correct, for three correct and for two correct structural formulas. Penalize missing hydrogens once only. Accept either full or condensed structural formulas. [4]

14 14 N15/4/EMI/P2/ENG/TZ0/XX/M increase in carbon chain; curly arrow going from lone pair/negative charge on N to ; curly arrow showing Br leaving; Accept curly arrow either going from bond between and Br to Br in 1-bromobutane/1-bromo-2-methylpropane or in the transition state. representation of transition state showing negative charge, square brackets and partial bonds; Do not penalize if N and Br are not at 180 to each other. Products: 3222N/(3 )22N and Br /KBr; [4] Penalize missing hydrogens and/or incorrect bond linkages (eg N instead of N ) only once in this question. Remember to apply EF from part (v). 3222N N2 OR (3 )22N 22 (3 )222N2 ; Ni / o / Ru; Accept Pt/Pd/u/Rh. Accept either chemical symbol or name.

15 15 (c) N15/4/EMI/P2/ENG/TZ0/XX/M O Br + 2O + Br 25 3 OR O 3 + 2O + Br 3 Br 3 curly arrow going from lone pair/negative charge on O in O to on ; Do not allow curly arrow originating on in O. curly arrow going from bond to form bond; curly arrow showing Br leaving; O Br / 2 (3)2 2O Br ; [4] Accept NaBr for Br. Remember to apply EF from part (v). Do not penalize if mechanism shown with a secondary bromoalkane. Do not penalize incorrect side-chain. Penalize missing hydrogens only once in this question. addition; (25) 2 (25) 2 / (3)2 2 (3)2 2 ; ontinuation bonds required for the mark.

16 16 (d) N15/4/EMI/P2/ENG/TZ0/XX/M Initiation: UV/ hf / h / heat l2 2l ; Reference to UV light or high temperatures must be included. Propagation: l l ; 25 l2 25l l ; Termination: l l l2 / 25 l 25l / ; Accept representation of radical without (eg, l, 25) if consistent throughout mechanism. Accept further chlorination. Award [3 max] if initiation, propagation and termination are not stated or are incorrectly labelled for equations. Accept correct description of processes without equations. Award [3 max] if Br used correctly instead of l. [4]

Markscheme November 2015 Chemistry Standard level Paper 2

N15/4/CHEMI/SP2/ENG/TZ0/XX/M Markscheme November 2015 Chemistry Standard level Paper 2 14 pages 2 N15/4/CHEMI/SP2/ENG/TZ0/XX/M This markscheme is the property of the International Baccalaureate and must