Electrolysis is the decomposition of an electrolyte into its elements using a direct electric current.
Electrolysis is the decomposition of an electrolyte into its elements using a direct electric current. Malay: elektrolisis · Chinese: 电解.
For electrolysis to happen the electrolyte must contain freely moving ions, which is why it works only for molten ionic compounds or aqueous solutions. When the current flows, cations move to the cathode and are reduced by gaining electrons, while anions move to the anode and are oxidised by losing electrons. Electrolysis is therefore a redox process driven by an outside supply of electrical energy. The products depend on whether the electrolyte is molten or aqueous, on the concentration, and on whether the electrodes are inert or active.
Example. In the electrolysis of molten lead(II) bromide, lead ions are discharged at the cathode to form molten lead (Pb2+ plus 2e- to Pb) and bromide ions are discharged at the anode to form bromine vapour (2Br− to Br2 plus 2e-). The compound is broken down into its two elements, which is exactly what the definition describes.
Confusion to avoid. Do not confuse electrolysis with the simple conduction of electricity. A metal wire conducts without changing, but an electrolyte is chemically decomposed as it conducts. Also keep electrolysis, which uses electrical energy to force a change, separate from a voltaic cell, which produces electrical energy from a spontaneous change.
Three deciding factors. For an aqueous electrolyte the product at each electrode is decided by three things together: the position of the ions in the electrochemical series, the concentration of the solution, and whether the electrode is inert or active. Changing any one of them can change the gas or metal you collect, which is why the same salt solution can give different products under different conditions, and why exam questions always state the concentration and the electrode material.
Electrolysis brings together electrodes, the electrochemical series and selective discharge, and it is applied in electroplating, the purification of copper and the extraction of reactive metals, so it is one of the most heavily tested ideas in SPM Chemistry.
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