Lifelong Learning Programme

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Chemistry is all around us
Copyright 2015
This project has been funded with
support from the European Commission

Educational Packages

Chemistry and Art

Chemistry and Metal Objects of Cultural Heritage

Step 3 - Activities

Evans experiment.
Make a solution of 3 g NaCl, 0.1 g K3Fe(CN)6 and 10 drops of phenolphthalein solution into 100 ml water. Take a piece of steel sheet, grind it with grinding paper and clean it in acetone. Put a drop of the solution on cleaned metal surfaced and observe the colour changes of the drop (Fig. 1).

After a while, outskirt of the drop turns pink and the center blue. Pink colour is caused by phenolphthalein detection of alkalinity. In this place, reduction of air oxygen is more intensive. On the other hand, air oxygen cannot reach the center of the drop and so reduction of iron is more intensive in the middle of the drop. Forming ferrous ions react with K3Fe(CN)6 and it leads to formation of blue sediment.

Fig. 1 Result of the Evans experiment (in the red box).

Fig. 2 Wassily Kandinski – Farbstudie Quadrate.