EasyChemistryHigh School (11–12)The d- and f-Block Elements › Transition Elements (d-Block)NumericalA-Level IB

A 7.90 g sample of pure potassium permanganate, with a molar mass of 158 g/mol, is heated until it…

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A $7.90\ \text{g}$ sample of pure potassium permanganate, with a molar mass of $158\ \text{g/mol}$ , is heated until it stops giving off gas: $2\text{KMnO}_4 \rightarrow \text{K}_2\text{MnO}_4 + \text{MnO}_2 + \text{O}_2$ . Find the moles of permanganate, the mass of oxygen given off and the mass of solid left.

Need a reminder? The key ideaShow

Moles = mass in g divided by molar mass in g/mol, or concentration in mol/L times volume in litres. Take every mole ratio from the balanced equation, and follow the chain one step at a time.

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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