HardChemistryHigh School (11–12)Organic Compounds with Functional Groups › Alcohols, Phenols and EthersNumerical

A 25.0 mL sample of old ether is shaken with excess acidified potassium iodide…

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A $25.0\ \text{mL}$ sample of old ether is shaken with excess acidified potassium iodide. The peroxide $\text{ROOH}$ oxidises iodide to iodine: $\text{ROOH} + 2 \text{I}^{-} + 2 \text{H}^{+} \to \text{ROH} + \text{H}_{2}\text{O} + \text{I}_{2}$ . The iodine is titrated with $0.0100\ \text{mol/L}$ sodium thiosulphate, and $4.60\ \text{mL}$ is needed. Two thiosulphate ions react with each $\text{I}_2$ . Find the amount of thiosulphate in micromoles, the amount of peroxide in micromoles, and the peroxide in mg per litre of ether, expressed as hydrogen peroxide (molar mass $34.015\ \text{g/mol}$ ).

Need a reminder? The key ideaShow

One mole of an ideal gas occupies $\dfrac{RT}{P}$ : $24.46\ \text{L}$ at $25\ ^\circ\text{C}$ and $101.325\ \text{kPa}$ . The lower flammable limit of ether vapour is $1.9\ \%$ by volume. A titration gives moles of thiosulphate, and two thiosulphate ions react with each $\text{I}_2$ . An activating group directs to the ortho and para carbons.

The worked solution

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