CAIE A-Level Chemistry A2 25.2 Partition Coefficients Questions

Procaine is used as an anaesthetic in medicine. It can be synthesised from methylbenzene in five steps as shown in Fig. 7.1.

Iodine is found naturally in compounds in many different oxidation states.

Procaine is used as an anaesthetic in medicine. It can be synthesised from methylbenzene in five steps as shown in Fig. 7.1.

Explain what is meant by partition coefficient, $K_{\mathrm{pc}}$.

Iodine is found naturally in compounds in many different oxidation states.

Iodide ions, $\mathrm{I}^{-}$, react with acidified $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})$ to form iodine, $\mathrm{I}_{2}$, and water. This reaction mixture is shaken with cyclohexane, $\mathrm{C}_{6} \mathrm{H}_{12}$, to extract the $\mathrm{I}_{2}$. Cyclohexane is immiscible with water.

$15.0 \mathrm{~cm}^{3}$ of $\mathrm{C}_{6} \mathrm{H}_{12}$ is shaken with $20.0 \mathrm{~cm}^{3}$ of an aqueous solution containing $\mathrm{I}_{2}$ until no further change is seen.
It is found that 0.390 g of $\mathrm{I}_{2}$ is extracted into the $\mathrm{C}_{6} \mathrm{H}_{12}$.
The partition coefficient of $\mathrm{I}_{2}$ between $\mathrm{C}_{6} \mathrm{H}_{12}$ and water, $K_{\mathrm{pc}}$, is 93.8.
Calculate the mass of $\mathrm{I}_{2}$ that remains in the aqueous layer.
Show your working.
mass of $I_{2}$ in aqueous layer =

Iodine is found naturally in compounds in many different oxidation states.

Iodide ions, $\mathrm{I}^{-}$, react with acidified $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})$ to form iodine, $\mathrm{I}_{2}$, and water. This reaction mixture is shaken with cyclohexane, $\mathrm{C}_{6} \mathrm{H}_{12}$, to extract the $\mathrm{I}_{2}$. Cyclohexane is immiscible with water.

Suggest how the value of $K_{p c}$ of $\mathrm{I}_{2}$ between hexan-2-one, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{COCH}_{3}$, and water compares to the value given in (a)(ii). Explain your answer.