Four esters, $$\(\mathbf{A}, \mathbf{B}, \boldsymbol{C}\)$$ and $$\(\mathbf{D}\)$$, with the molecular formula $$\(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{2}\)$$ are shown in Fig. 7.1. A mixture of these esters, A, B, C and D, is analysed by gas-liquid chromatography. The chromatogram produced is shown in Fig. 7.2. The number above each peak represents the area under the peak. The area under each peak is proportional to the mass of the respective ester in the mixture. (i) State what is meant by retention time. ....................................................................................................................................... . ................................................................................................................................. (ii) Calculate the percentage by mass of ester $$\(\mathbf{D}\)$$ in the original mixture. percentage by mass of ester $$\(\mathbf{D}=\)$$ .......................... \%

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