The permanganate experiment

In activity 17.2 the only thing that changes is the temperature. The solutions, the volumes and the nails are all kept the same.

Activity 17.2

You will need: 2 iron nails of the same size, water, dilute potassium permanganate (KMnO₄) solution, dilute sulphuric acid (H₂SO₄), a stopwatch, two test tubes, a burner.

Make up a very dilute potassium permanganate solution.
Put equal volumes of it into two test tubes, and add equal amounts of sulphuric acid to those volumes.
Heat one of the tubes to a somewhat higher temperature.
Drop the same number of equal, well-cleaned iron nails into both tubes.
Using a stopwatch, measure how long the solution in each tube takes to change colour.

Figure to be added

The two test tubes: acidified KMnO₄ solution on the left and heated acidified KMnO₄ solution on the right, each with its clean iron nail (activity 17.2).

What we watch here is a colour change. The purple of the potassium permanganate fades as it reacts with the iron, so the fading of the colour marks the end of the reaction.