Question

Account for the following observations which were made when concentrated sodium chloride solution, to which a little universal indicator had been added, was electrolyzed in the laboratory in a Hofmann voltameter.
a The universal indicator initially turns red in the region of the anode, but as the electrolysis proceeds it loses its color.
b The universal indicator turns blue in the region of the cathode.

Answer 1

a) Since acidity is a measure of the excess of hydrogen ions in solution (H+), the left behind hydrogen ions make the solution near the positive electrode acidic, which turns the indicator solution red. ... After the electrodes have been disconnected.