This question is about lipids and biofuels. Octanoic acid, CH3(CH2)6COOH\text{CH}_3(\text{CH}_2)_6\text{COOH}CH3(CH2)6COOH, can be obtained from the acidic hydrolysis of tricaprylin, a triester found in coconut oil and palm kernel oil.
Complete the equation for the hydrolysis of tricaprylin under acidic conditions: CH3(CH2)6COO−CH2∣CH3(CH2)6COO−CH∣CH3(CH2)6COO−CH2+3H2O→H+…\begin{array}{l}\text{CH}_3(\text{CH}_2)_{6}\text{COO}-\text{CH}_2 \\ \quad | \\ \text{CH}_3(\text{CH}_2)_{6}\text{COO}-\text{CH} \\ \quad | \\ \text{CH}_3(\text{CH}_2)_{6}\text{COO}-\text{CH}_2 \end{array} + 3\text{H}_2\text{O} \xrightarrow{\text{H}^+} \dotsCH3(CH2)6COO−CH2∣CH3(CH2)6COO−CH∣CH3(CH2)6COO−CH2+3H2OH+…
Octanoic acid can be used as a biofuel. A student investigated its enthalpy of combustion using the simple calorimetry apparatus shown below:
In this experiment, combustion of 432 mg432 \text{ mg}432 mg of octanoic acid released energy that increased the temperature of 0.150 kg0.150 \text{ kg}0.150 kg of water from 20.2 ∘C20.2 \text{ }^\circ\text{C}20.2 ∘C to 40.5 ∘C40.5 \text{ }^\circ\text{C}40.5 ∘C.
Calculate a value, in kJ mol−1\text{kJ mol}^{-1}kJ mol−1, for the experimental enthalpy of combustion of octanoic acid in this experiment. Give your answer to an appropriate number of significant figures. (The specific heat capacity of water is 4.18 J K−1 g−14.18 \text{ J K}^{-1}\text{ g}^{-1}4.18 J K−1 g−1).
State how the value calculated in Part (b) is likely to differ from standard data book values. Give one reason, other than heat loss to the surroundings, for this difference.