| Date | November 2011 | Marks available | 2 | Reference code | 11N.3.sl.TZ0.F1 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Deduce | Question number | F1 | Adapted from | N/A |
Question
A healthy diet consists of a range of food groups in the right proportions that provide the energy for the body to function, grow and repair itself.
Examples of straight-chain fatty acids include \({{\text{C}}_{{\text{19}}}}{{\text{H}}_{{\text{39}}}}{\text{COOH}}\), \({{\text{C}}_{{\text{19}}}}{{\text{H}}_{{\text{31}}}}{\text{COOH}}\) and \({{\text{C}}_{{\text{19}}}}{{\text{H}}_{{\text{29}}}}{\text{COOH}}\).
State the empirical formula and structural features of monosaccharides.
Deduce the structural formula of a triester formed from three long-chain carboxylic acid molecules, RCOOH, and one propane-1,2,3-triol molecule, \({\text{HO–C}}{{\text{H}}_{\text{2}}}{\text{CH(OH)–C}}{{\text{H}}_{\text{2}}}{\text{OH}}\). Identify one of the ester linkages in the structure by drawing a rectangle around it.
Deduce the number of C=C bonds present in one molecule of each fatty acid.
\({{\text{C}}_{{\text{19}}}}{{\text{H}}_{{\text{39}}}}{\text{COOH}}\):
\({{\text{C}}_{{\text{19}}}}{{\text{H}}_{{\text{31}}}}{\text{COOH}}\):
\({{\text{C}}_{{\text{19}}}}{{\text{H}}_{{\text{29}}}}{\text{COOH}}\):
Markscheme
\({\text{C}}{{\text{H}}_2}{\text{O}}\);
Accept (CH2O)n
one carbonyl/C=O and (at least two) hydroxyl/OH groups;
Award [1] for structure that shows unambiguously how the atoms are arranged together.
Award [1] for identifying one of the three ester linkages – must not include R and/or CH2.
\({{\text{C}}_{19}}{{\text{H}}_{39}}{\text{COOH}}\): 0
\({{\text{C}}_{19}}{{\text{H}}_{31}}{\text{COOH}}\): 4
\({{\text{C}}_{19}}{{\text{H}}_{29}}{\text{COOH}}\): 5
All three [2], any two [1], any one [0].
Examiners report
The vast majority of candidates were able to state the empirical formula of monosaccharides, but a good number were not able to state its structural features.
It was surprising to see that only about half could deduce the structure of the triester correctly and identify the ester linkage.
About half of the candidates were able to deduce the number of C=C bonds correctly from the list of fatty acids.
