MJC H2 Chem 2013 Prelim P3 Soln

Mark Scheme CONFIDENTIAL ©chemistry@meridian jc 1 1(a) (i) No of moles of NO2 gas produced = 561.01 10 57.6 10 8.31 353    Mr of fexofenadine = -3 1 1.983 10 = 504 (ii) There are significant intermolecular forces of attraction (iii) The R group should be C6H5 since R =77 (b) (i) The hydrochloride salt is more so luble in aqueous solution forming ion- dipole interaction with the water molecules (ii) No of boxes he needs for 5 days = 425 30   = 2 (must be whole no)   (c) (i) CN O Cl         CN N RR HO OH   Compound A Compound B (ii) Electrophilic substitution (iii) NaBH4 in ethanol,r.t.p (iv) COOD O Cl (v) Concentrated H2SO4, heat Suggested Answers for 2013 MJC Prelim P3 939

©chemistry@meridian jc 2 (d) (i) Initiation Br2 2B r Propagation Br CN UV light HBr CN CN Br2 CN Br Br Termination Br CN CN Br     (ii) The formation of the iodo derivative in the propagation step is highly endothermic .   (e) The amine group. The electron donating R gr oup in the amine increase the electron density on the lone pair of electrons on N, making it more available to accept a proton. 2(a) (i) CH3CH(OH)CH3  CH3COCH3 + 2 H+ + 2e CH3CH(OH)CH3 + O2  CH3COCH3 + 2H2O (ii) Eθ = - 0.03 V (iii) The OH- neutralises H + , causing the concentration [H +] to decrease. The equilibrium position will shift left to increase [H +]. Eθ oxid will become less positive. Hence, more positive overall Eθ cell . (iv) Availability of propan-2-ol as source. *Other answers possible (b) (i) [Pt(NH3)4]2+ (aq) + 2e  Pt (s)+ 4NH3 (g). Grey solid formed or pungent ammonia gas evolved ( or state test for ammonia) (ii) No of moles of platinum = ூ் ௡ி = = 2.04 x10-3 Mass of platinum = 2.04 x 10 -3 x 195 = 0.398 g 940

©chemistry@meridian jc 3 (c) (i) P undergoes acid-carbonate reaction / neutralization with NaHCO 3  P contains a carboxylic acid group.  P undergoes electrophilic addition with aq chlorine  P contains an alkene  Q undergoes electrophilic addition and electrophilic substitution with aq chlorine.  Q contains both an alkene and a phenol  Q undergoes oxidation with Tolle n’s reagent but not Fehling solution  P contains an aromatic aldehyde  P and Q undergoes strong oxidation with hot acidified KMnO 4 to give T and U respectively  P has only one R group attached to the benzene ring and Q contains three R groups attached to the benzene . 941

©chemistry@meridian jc 4 (ii) Equation (iii) Compound X is the stronger acid. The distance of Br atom on X is nearer to the COOH/COO - group .Electron-withdrawing effect on –COO - / carboxylate ion hence stabilisation of conjugate base wrt acid for: X > Y. 3(a) (i) HN N N OR HN N N (ii) C O N H (iii) CH3CH2CHO CH3CH2N H C O CH3 CH3CH2COOH CH3CH2NH2 KMnO4,d i lH2SO4 heat HN3,H + cat CH3COCl     (b) 2Fe2+ + S2O8 2-  2Fe3+ + 2SO4 2- E cell = 2.01 – 0.77= +1.24 V > 0 2Fe3+ + 2I - +  2Fe2+ + I2 E cell = 0.77 – 0.54= +0.23 V > 0 Both steps are kinetically more favourable since oppositely charged ions are involved and attract each other hence lowering the Ea.   942

©chemistry@meridian jc 5 (c) Reaction I: nucleophile ; Reaction II: electrophile (d) (i) SN1 CB r H3C H H3CH2C  slow C CH3 H CH2CH3 C CH3 H CH2CH3 N3 - CN 3 H3C H H3CH2C   (ii) Equal probability of nucleophilic attack of the trigonar planar carbocation from top and bottom of the plane forming a racemic mixture. (e) Hydration of MgCl2 : MgCl2 (s) Mg 2+ (aq) + 2Cl- (aq) Partial hydrolysis of MgCl2 [Mg(H2O)6]2+(aq) [Mg(H 2O)5(OH)]+(aq) + H+(aq) pH= 6.5 (f) (i) A= 0 ; B = 1; C = 1 (ii) CH3CH2 C CH2OH CH3 OH CH3CH2 C CHO CH3 OH    A B C H3C N CH2OH CH3CH2 C 4(a) Ga2 dimers are simple molecular ; Aluminium has a giant metallic lattice. Less energy is required to overcome the weak Van der Waals’ forces than the stronger electrostatic attractions between the cations and delocalised electrons. Hence, Ga2 has lower melting point. (b) (i) Increase of mobile electrons to conduct electricity. (ii) Electrons (from nearby/neighbouring atoms) are able to move/mobile to occupy the ‘holes’.  O H2 943

©chemistry@meridian jc 6 (c) (i) ∆Hf o (GaCl3) = -577 kJ mol-1 (ii) Polarisability / extent or ease of polarisation : C l– < Br – < I– . Hence, covalent character : GaCl3 < GaBr3 < GaI3 leading to greater difference between experimental and theoretical value. (iii) Dot and cross diagrams Ga F x 3 3+ -     gallium(III) fluoride   Ga Cl Cl Cl x xx Ga Cl Cl Cl xx x     gallium(III) chloride To minimise repulsion, t he 4 electron pairs are dire cted to the corners of a tetrahedron. Shape around each Ga is tetrahedral with bond angle of 109.5o. Ga3+(g) + 3Cl (g) + 3e 3rd IE Ga2+(g) + 3Cl (g) + 2e 3(1 st EA) 2nd IE Ga+(g) + 3Cl (g) + e 1st IE Ga(g) + 3Cl (g) 3  ∆Hat o (Cl) Ga(g) + 3/2 Cl2(g) ∆Hlatt o (GaCl3) ∆Hat o (Ga) Ga(s) + 3/2 Cl2(g) ∆Hf o ( GaCl3) GaCl 3(s) Ga3+(g) + 3Cl-(g) 0 944

©chemistry@meridian jc 7 (d) (i) Kp = 3(1.8) 1.6 = 3.65 atm2 (ii) The formation is favoured by low pressure. The  equilibrium position shifts right towards an increase in no of moles of gas (iii) S is positive since there is an increase in number of gas molecules. At low temperatures, G is positive becaus e of the positive H. At higher temperatures, the negative –T S outweighs H, and so G becomes negative. Conditions required are a hi gh temperature. to ensure a high rate and feasibility of reaction proceeding. 5(a) Primary Structure – covalent bonds ( in amide / peptide linkage) Secondary Structure – hydrogen bonds Tertiary Structure – R group interactions Quaternary Structure – Van der Waal’s forces, ionic, hydrogen bonding (b) A: Glutamic acid; B: Asparagine ; C : Valine (c) (i) pH = -lg (3 x 10-10) = 9.50 (ii) [NH2OH] formed at eq. point = -31.44? 0 14.40+25.0 1000 [OH-] = -80.03654 1.10 10  = 2.00 x 10-5 mol dm-3 pOH = 4.70 hence pH = 9..30. Phenolphthalein is suitable as the pH transition range of the indicator (8.5 – 10.5) lies within the rapid pH change over the equivalence point (pH 9.3). (d) (i) Order of reaction with respect to PO2 is 1 (ii) Order of reaction with respect to hemoglobin is 1. When concentration of hemoglobin was halved, change in the gradient of the graph is halved and rate of reaction was halved also. (iii) Rate = k [hemoglobin][O2] (iv) Rate = 2.68 x 10-5 mol dm-3 s-1    945

©chemistr (e) (f) ry@meridian jc (i) Ea is particle of reac (ii) 1 Den sec with 2 Pro OR bon hyd (i) Est (ii) lowered d es and he n ction α freq naturation condary, te hin the prim otonates t h R the basi c nd betwee drogen bon ter group due to an nce freque quency of e refers t o ertiary and mary struct he anionic c amino g r n the cha r nding effec 8 alternativ ency of eff e effective co o the br e quaternary ture. group, - C roup, -NH 2 rged R gr o ct as well ve reactio n ective colli ollisions, ra eaking of y structure COO- foun 2 found i n oups of - n pathwa y sions incre ate of react weak bo e but not th d in gluta m lysine, a n COO- and y. No of r eases. Sin tion increa onds holdi he covalen mic acid r nd disrupt d -NH 3 + . A reactant nce rate ases. ng the t bonds residue s ionic Accept 946