Hofmann voltameter

The Hofmann water electrolysis unit, Hofmann decomposition apparatus or water decomposition apparatus according to Hofmann is a device for the electrolytic decomposition of aqueous solutions and was named after August Wilhelm Hofmann (1818-1892), who described this experimental setup, for example, in his 1866 published book. The experimental setup was used as a coulomb meter.

Function

He used to demonstrate the electrolytic decomposition of water, for example. In this case, the entire apparatus is often filled with dilute sulfuric acid, because pure water does not have sufficient electrical conductivity. After applying a DC voltage to the platinum electrode or carbon electrode takes place the evolution of gas at the cathode and anode.

The water is decomposed into oxygen and hydrogen, its two components. The gases collect in the two measuring tubes and can be removed with the help of a rooster. For better power management, the solution is often enriched with an acid or alkali, and sodium chloride (NaCl) is suitable. Attention chlorine gases form!

At the cathode, the oxonium ions, which are formed by proteolysis of zugesetzen acid, are reduced to hydrogen and oxidized at the anode, the water to oxygen and oxonium ions.

Cathode reaction:

Anode reaction:

Overall reaction:

The ratio of gas volume in the legs is thereby 1: 2 ( oxygen: hydrogen ) amount. However, this ratio can not come into existence precisely because the oxygen in the water dissolves better in the beginning than hydrogen. To circumvent this problem, the experiment should run with open taps for a few minutes before.

Operation

The positively charged oxonium ions that are in the vicinity of the negatively charged electrode, the cathode, are, are attracted by the negative charge and there discharged under release of hydrogen ( cathodic reduction ). In the positively charged electrode, the anode, electrons are removed from the water ( anodic oxidation). The oxidized water particles are unstable and decompose to release oxygen and formation of oxonium ions. The oxonium ions do not migrate through the solution to the cathode, they just give their positive charge through a rearrangement of hydrogen bonds by the solution to the cathode on. Figure: Proton conduction proton conduction in water is called This form of electric line.