This electricity is added by putting electrodes into the solution which are hooked up to the positive and negative pole or terminal of a power source, such as a battery. Electrodes are classified as either cathodes or anodes.

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Electrolysis is often used to produce pure hydrogen from sodium chloride (NaCl) and water (H2O). Electricity is introduced to the mixture of salt and water, and the elements recombine to form chlorine gas (Cl), hydrogen gas (H) and sodium hydroxide (NaOH).