(a)     Describe the differences in the structure between the saturated fatty acid \({{\text{C}}_{{\text{16}}}}{{\text{H}}_{{\text{32}}}}{{\text{O}}_{\text{2}}}\) and the unsaturated fatty acid \({{\text{C}}_{{\text{16}}}}{{\text{H}}_{{\text{26}}}}{{\text{O}}_{\text{2}}}\).

(b)     Describe how \({{\text{C}}_{{\text{16}}}}{{\text{H}}_{{\text{26}}}}{{\text{O}}_{\text{2}}}\) can be converted to \({{\text{C}}_{{\text{16}}}}{{\text{H}}_{{\text{32}}}}{{\text{O}}_{\text{2}}}\).

(c)     Fatty acids are components of fats and oils.

(i)     Describe one advantage of the products formed by hydrogenating fats and oils.

(ii)     Describe one disadvantage of the products formed by hydrogenating fats and oils.

(a)     unsaturated fatty acid has (3) C=C double bonds;

saturated fatty acid has only single C–C bonds;

unsaturated fatty acid can display cis and trans isomerism / saturated fatty acid cannot display cis and trans isomerism;

saturated fatty acid chains are straighter than unsaturated chains / OWTTE;

(b)     hydrogen/ 2 H /hydrogenation;

(high pressure and) high temperature/any temperature in the range of 150 °C to 200 °C /heat;

catalyst/nickel/Ni/platinum/Pt/copper/Cu/zinc/Zn;

(c)     (i)     semi-solid/solid fat/lipid (with higher melting point);

decreased rate of oxidation/stability increases with increasing saturation;

increased hardness;

control feel and plasticity/stiffness;

hydrogenated vegetable fats are cheaper than animal fats;

(ii)     (trans fatty acids can be formed from partial hydrogenation of fats and oils)

(trans fatty acids) are difficult to metabolize/accumulate in fatty tissue/are difficult to excrete;

(trans fatty acids) increase the levels of LDL cholesterol;

(trans fatty acids) are a low quality energy source;

mono- and poly-unsaturated fats are healthier (for the heart) than saturated fats;

This was generally not well done, with many candidates in the first part failing to note the degree of unsaturation as well as not specifying it was carbon-carbon bonds they were referring to. In Part (b) the conditions for hydrogenation reactions appeared not to be well known, though many candidates gained some marks on the advantages and disadvantages of hydrogenated fats, though the latter often lacked the required precision.