Calculate the number of carbon-carbon double bonds in linolenic acid, \({{\text{C}}_{{\text{18}}}}{{\text{H}}_{{\text{30}}}}{{\text{O}}_{\text{2}}}\), given that 7.7 g of iodine, \({{\text{I}}_{\text{2}}}\), react with 2.8 g of linolenic acid.

3 C=C double bonds;

3 C=C double bonds scores [2].

No ECF.

Many candidates were able to solve this straight forward calculation question. The major errors candidates made included comparing the ratio of the masses provided rather than working out the ratio of the number of moles of linolenic acid to iodine. In this instance candidates were not awarded any marks because they clearly did not understand the concepts involved. Candidates could also calculate the number of carbon-carbon bonds from the formula of linolenic acid.