Definition - What does Hydrolysis mean?

Hydrolysis is the chemical process of decomposition or alteration of a chemical substance by water. It is a reaction involving the breaking of a bond in a molecule using water. The reaction mainly occurs between an ion and water molecules and often changes the pH of a solution. This can cause metallic corrosion through oxidizing metals.

In aqueous solutions of electrolytes, it produces weak base by the reactions of cations with water or weak acid by reactions of anions with water, which can lead to corrosion.

Corrosionpedia explains Hydrolysis

Hydrolysis is a chemical process in which a certain molecule is split into two parts by the addition of a molecule of water. One fragment of the parent molecule gains a hydrogen ion (H+) from the additional water molecule. The other group collects the remaining hydroxyl group (OH-). The reactants other than water, and the products of hydrolysis, may be neutral molecules — as in most hydrolysis involving organic compounds — or ionic molecules, as in hydrolysis of salts, acids and bases.

The most common hydrolysis occurs when a salt of a weak acid or weak base (or both) is dissolved in water. Water auto-ionizes into negative hydroxyl ions and positive hydrogen ions.

Hydrolysis can cause metallic corrosion, which can produce very corrosive environments through the chemical change of water into acid. This phenomenon is particularly noticeable when the environment is confined, such as in most forms of localized corrosion (pitting, crevice, environmental cracking). The chemical change in question is true of most metals since the metallic ions produced by the corrosion processes are not soluble in their ionic forms. These ions then react and form more stable species such as oxides and hydroxides. For example, hydrolysis of the aluminum ions in an aluminum window causes aluminum corrosion through acidification of the crevice.

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