Must make reference to the delocalised e in graphite ii Before 4 After 3 iii

Must make reference to the delocalised e in graphite

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Must make reference to the delocalised e in graphite. (ii) Before: +4 After: +3 (iii) Making use of dot and cross diagram to show the bonding pairs. 4 bond pair of bonding e , no lone pairs of e hence tetrahedral shape. (iv)
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H2 Chemistry 9647 2015 cold alkaline KMnO 4 or cold KMnO 4 and aq NaOH Common mistake: use K 2 Cr 2 O 7 or that the reagents should be heated (v) Condensation c (i) 2Li 2 O 2 + CO 2 Li 2 CO 3 + 1/2O 2 Common mistake: students did not write the correct formula for lithium carbonate or lithium peroxide and wrote LiCO 3 or LiO 2 . (ii) Li + has a small ionic radius and hence its charge density is high enough to distort the electron cloud of CO 3 2– , weakening the C–O bonds and allowing it to decompose thermally. NOTE: Need to be clear that it was the C-O bond in the carbonate ion that was polarised and that the cation has high charge density. d (i)
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H2 Chemistry 9647 2015 (ii) Common mistake: not relating the position of the OH group to the number of carbon atoms in each of the starting compounds and using RLi as one of the reagents instead of RBr. e Heat all three with acidified K 2 Cr 2 O 7 in a test tube. The one that remains orange is R. The other two will turn the orange K 2 Cr 2 O 7 to green. Test the oxidised product with 2,4-dinitrophenylhydrazine. The one that produces orange ppt is Q and the one without ppt is P. Common mistake: Used KMnO 4 to oxidise the alcohols. Colour change is purple to colourless. Did not heat the acidified K 2 Cr 2 O 7 . Use tri-iodomethane test to identify R. NOTE: need to isolate oxidised product before testing for it such as heating the alcohol with acidified oxidant with produce CO 2 due to the presence of acid.
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