2007 VJC Prelims Paper 1 FAQs

Explanation for Q3
ClO2- is bent, i.e. O=Cl--O-, where Cl has 10 e- around it (inclusive of 2 lone pairs) and O bears the negative charge. Bond angle of ClO2- is similar to that of H2O. About 105 degrees.

Explanation for Q32
Fix T. Then draw a vertical line upwards to cut both curves and extrapolate horizontally to get values for fraction of X. At a fixed T, more X is present when pressure is lower (2 x 10^7 Pa). By LCP, X must be on the side of the equation with more gas molecules.

The shapes of the curves tell us that when T increases, more X is present. By LCP, an increase in temperature favours an endothermic reaction. Thus, X must be the product of an endothermic reaction.

Explanation for Q37
Ethene must attack Br2 first to give a carbocation intermediate. After that, Cl-, H2O and Br- (from the original Br2) can attack the carbocation. Hence, the products must have Br in them.