Coconut oil contains a triester with three identical R groups. This triester reacts with potassium hydroxide to form propane-1,2,3-triol and a potassium carboxylate salt.
The triester in coconut oil has a relative molecular mass, Mr=638.0M_r = 638.0Mr=638.0. In this triester, the R group represents an alkyl group that can be written as CH3(CH2)n\text{CH}_3(\text{CH}_2)_nCH3(CH2)n. Deduce the value of nnn in CH3(CH2)n\text{CH}_3(\text{CH}_2)_nCH3(CH2)n. Show your working.
A 2.150 g2.150\text{ g}2.150 g sample of coconut oil is heated with 0.650 g0.650\text{ g}0.650 g of KOH\text{KOH}KOH (Mr=56.1M_r=56.1Mr=56.1) in aqueous ethanol until all of the triester is hydrolysed. The mixture is cooled. The remaining KOH\text{KOH}KOH is neutralised by exactly 26.85 cm326.85\text{ cm}^326.85 cm3 of 0.250 mol dm−3 HCl0.250\text{ mol\,dm}^{-3}\ \text{HCl}0.250 moldm−3 HCl. Calculate the percentage by mass of the triester (Mr=638.0M_r=638.0Mr=638.0) in the coconut oil. Show your working.
Suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH\text{KOH}KOH. Give a safety precaution used when heating the mixture and justify your choice.
22 exam-style questions on AQA A Level Chemistry Carboxylic acids and derivatives (A-level only), covering Carboxylic acids and esters (A-level only) and Acylation (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.