This experiment was inspired by an elder version of Bob Worley electrolysis
Two pencil leads -connected with a 9-Volt battery- touch a drop of copper(II)chloride solution. 5 x 5 mm filter papers are placed close to the electrodes. One of them is wetted with a tiny drop of blue petunia extract, the other one with a diluted potassium chloride solution. (more see below)
A solid with the colour of copper grows at the end of the negative electrode, bubbles are observed at the positive rod. After 1 minute the white paper close to the positive electrode starts to get brown.
The blue colour of the other paper changes to red. (Later on it is bleached).
Copper(II) chloride react leaving copper and chlorine CuCl2(aq) --> Cu(s)+Cl2g)
Chlorine oxydizes iodide. producing iodine Cl2(g) + 2 I- --> 2 Cl- + I2(s)
Chlorine reacts with water in the blue paper forming hydrochloric acid. German
First publication: 15.03.2014 Last modification: 14.10.2016