HardChemistryHigh School (11–12)The p-Block ElementsNumerical

A student passes sulphur dioxide through 25.0 mL of 0.0200 mol/L potassium permanganate solution…

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A student passes sulphur dioxide through $25.0\ \text{mL}$ of $0.0200\ \text{mol/L}$ potassium permanganate solution, acidified with dilute sulphuric acid. The gas is passed until the purple colour just disappears. The reaction is $2\text{MnO}_4^- + 5\text{SO}_2 + 2\text{H}_2\text{O} \rightarrow 2\text{Mn}^{2+} + 5\text{SO}_4^{2-} + 4\text{H}^+$ . Find the amount of permanganate, the amount of sulphur dioxide that was used, the volume of that gas at $273\ \text{K}$ and $1\ \text{atm}$ , and the amount of hydrogen ions produced by the reaction. Take $22.4\ \text{L}$ for $1\ \text{mol}$ of gas.

Need a reminder? The key ideaShow

Redox: electrons lost equal electrons gained. In iodometry, 2 mol of thiosulphate react with 1 mol of iodine. In a disproportionation one species forms two products with higher and lower oxidation states. In a puzzle, follow the clues one at a time: gas tests, colours and the reagents of the standard conversions. At 273 K and 1 atm, 1 mol of gas fills 22.4 L.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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