(i)     Calculate the heat required, in kJ, to raise the temperature of the water, using data in the table above and from Table 2 of the Data Booklet.

(ii)     Determine the enthalpy of combustion of the potato chip, in \({\text{kJ}}\,{{\text{g}}^{ - 1}}\).

This energy comes mainly from the combustion of triglycerides. State the name of one other type of lipid found in the body and one role, other than energy storage, of this type of lipid.

Name:

Role:

Explain why lipids have a higher energy content than carbohydrates.

(i)     \({\text{heat}} = \frac{{4.18 \times 20.0 \times (51.3 - 17.8)}}{{1000}}\);

\( = 2.80{\text{ (kJ)}}\);

(ii)     \({\text{enthalpy of combustion}} = \left( {\frac{{2.80}}{{0.421}} = } \right){\text{ }} - 6.65{\text{ (kJ}}\,{{\text{g}}^{ - 1}}{\text{)}}\);

Name:

steroids;

Role:

(sex) hormones;

OR

Name:

phospholipids;

Role:

membranes;

lipids less oxidized/contain less oxygen / carbohydrates partially/more oxidized/contain more oxygen / OWTTE;

This part was generally well answered but there were some cases where 33.5 °C was converted into Kelvin. Many candidates had serious problems with unit conversions and gave the answer as 2800 J or 2800 kJ. Some candidates had correct value for (ii) but lost the mark because of the omission of the negative sign.

Part (b) was well answered.

Very few candidates linked the fact that lipids have higher energy content due to being less oxidized.