What is the effect of 1 mol dm-3 hydrochloric acid on a bulb? explain why this effect happens.

Electrolysis of hydrochloric acid using the Hoffman voltameter with platinum electrodes (right diagram).  The Hofmann voltameter is filled with the electrolyte (hydrochloric acid) by opening the taps at the top of the outer tubes to allow any gas to escape. The gases formed on the electrolysis of the dilute hydrochloric acid can be collected via the same taps.

In the simple electrolysis cell (left diagram), the graphite (carbon) electrodes are, through a large rubber bung, 'upwardly' dipped into an solution of dilute hydrochloric acid. In this cheap and simple apparatus the gaseous products (hydrogen and chlorine) are collected in small test tubes inverted over the carbon electrodes. You have to fill the little test tubes with the electrolyte (dil. hydrochloric acid), hold the liquid in with your finger and carefully invert them over the nearly full electrolysis cell. The electrolysis will only take place when electricity is passed through the dilute hydrochloric acid solution.

In both experiments above the platinum or carbon electrodes are inert. You can also use the simple apparatus illustrated on the right, using two inert metal wire electrodes.