Electrolysis in Experiment

In electrolysis of aqueous solutions you must use unreactive materials (such as graphite) for electrodes to prevent unwanted reactions between the electrode and the solution. Aqueous salt solutions contain hydrogen, hydroxide, metal and non metal ions. In dilute halide salt solutions the oxygen ions outnumber the halide ions so oxygen forms at the anode.

There can be many products of the electrolysis of aqueous solutions including hydrogen, oxygen or halide gases and solid metals. You can determine which gas is produced as oxygen gas will relight a glowing splint, hydrogen gas will put out a glowing splint and chlorine gas turns damp blue litmus paper red.

In the electrolysis of molten salts only the metal and non metal ions of the salt are present (no hydrogen or hydroxide from water). The salt must be melted by a heat source, e.g. bunsen burner. Electrolysis of lead bromide is commonly used to demonstrate molten salt electrolysis due to its relatively low melting point.

In molten electrolyte electrolysis, a metal is always formed at the cathode and non-metal is formed at the anode. Halide gases such as chlorine or bromine are commonly produced. Bromine gas is brown and pungent smelling.

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