2020_DHS-RVHS-TJC_H3_Prelim_Key

1 © DHS / RVHS / TJC 2020 9813/01 [Turn Over Section A 1 (a)  The electrochemical epoxidation can be ran at ambient conditio ns, compared to the high T and P of the silver–based method.  The current methods may produce CO 2 due to overoxidation, leading to an increased carbon footprint  Water is an abundant / safe / sustainable oxygen source compar ed to flammable mCPBA  Generates useful H 2 (g) side–product  Higher atom efficiency compared to the mCPBA method that produ ces a large amount / stoichiometric amounts of RCOOH sideproduct. ( b ) ( i ) (ii) No. of mol of cyclooctene oxide = ହ଴ ଵଶ଺݈݋݉ No. of mol of electrons req = ൈ 2 ൈ ଵ଴଴ ଷ଴ ݈݋݉ Total charge = ܥ c ) ( i ) The Mr of the product epoxide can be determined using mass spectrometry. The molecular ion peak is expected to increase from 126 to 128 if the oxygen source was H218O. (ii)  Use renewable electricity/ development of renewable energy sou rces/ low cost technology that generate electricity e.g. solar cells  Use renewable chemical feedstock e.g. CO 2 / create renewable ethene instead of fossil–fuel derived ethene  Optimising conditions to improve yield of epoxide over ketone  Understanding mechanism for ketone formation  Increase the yield of epoxide by increasing the selectivity to epoxide with which it’s created.  Changing a catalyst to improve selectivity for epoxide over ke tone  Modify the electrolyte to improve the interaction between ethe ne and the anode. ( d ) Since water is in large excess, the reaction is pseudo–zero ord er with respect to [H2O]. Let n be the order of reaction with respect to [cyclooctene]. rate = k’[cyclooctene] n Taking logarithms on both sides of the equation, ሿ

2 © DHS / RVHS / TJC 2020 9813/01 ൌ െ2.56 െ ሺെ3.52ሻ െ0.8 െ ሺെ2.16ሻ ൌ 0.7059 Hence the order of reaction with respect to [cyclooctene] is 0.7. ( e ) ( i ) Ring strain in a 3–membered ring, where the bond angle is constrained to 60° instead of 109.5° f o r t h e s p3–hybridised atoms / additional repulsion between bond pairs destabilises the ring (ii) CH2=CH2 (g) + H2O (l) → H2 (g) + (g) H = ∑BEreactants – ∑BEproducts = BE(C=C) + 2(O–H) + Hvap – [ BE(H–H) + BE (C–C) + 2BE(C–O) – 105] = 610 + 2(460) + 40.8 – [ 436 + 350 + 2(360) – 105 ] = +169.8 kJ mol‒1 (iii) S > 0 as the number of gaseous particles increases from 1 to 2 m ol as the reaction proceeds. Since G = H – TS and |TΔS| increases as temperature increases, G becomes less positive /more negative, reaction becomes more spontaneous. [Total: 16] -3.6 -3.4 -3.2 -3 -2.8 -2.6 -2.4 -2.2 -2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 lg (rate) lg [cyclooctene]

3 © DHS / RVHS / TJC 2020 9813/01 [Turn Over 2 (a) (i) Compare the angles of rotation of plane–polarised light by the enantiomerically pure reactant and the stereoc