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Hydrolysis is a chemical reaction between water and another compound, breaking chemical bonds in both molecules. It occurs in some ionic compounds, essential life processes, soap making, and rock erosion. Hydrolysis is used in breaking down food into nutrients and in industrial processes. It is also important in rock weathering, forming soils and making minerals available to plants.
Hydrolysis is a type of chemical reaction that occurs between water and another compound. During the reaction, chemical bonds are broken in both molecules, causing them to break apart. The water molecule splits to form positively charged hydrogen (H+) and hydroxide (OH-) ions, and the other molecule splits into two simpler sections, also with positive and negative charges. H+ and OH- ions bind to each of these sections. These reactions occur when some ionic compounds, for example certain acids, bases and salts, dissolve in water; are involved in processes that are essential for life; they are used in some important industrial processes, such as soap making; and play an important role in the erosion of rocks.
Ionic compounds
Ionic compounds can be acids, bases, or salts, which are compounds that result from the reaction of an acid and a base. They consist of positively charged cations and negatively charged anions. When dissolved in water, they split into their cations and anions. Anions of weak acids and cations of weak bases will react to some extent with water, resulting in hydrolysis.
When a salt is the product of a strong acid and a weak base, the base cation will hydrolyse in water. For example, ammonium chloride (NH4Cl) is the salt of a weak base – ammonia (NH3) – and a strong acid – hydrochloric (HCl). When dissolved in water, it splits into cations and anions, NH4+ and Cl-, respectively. The cation, however, will react with water to some extent to lose a hydrogen ion:
NH4+ + H2O NH3 + H3O+
Since this reaction produces hydronium ions (H3O+), the resulting solution is acidic. When a salt is the product of a strong base and a weak acid, the anions of the acid will react with water accepting hydrogen ions (H+), leaving hydroxide ions (OH-), which gives an alkaline solution. The salt of a strong acid and strong base will not hydrolyze because the anion of the acid and the cation of the base do not react with water.
Vita
Many processes essential to life involve hydrolysis. An example is the release of energy by the molecule adenosine triphosphate (ATP). Cells use this compound to store energy, which can then be released when needed. The molecule has three phosphate groups (PO4-), but can lose one of these groups by reacting with water. This reaction actually consumes a small amount of energy, but much more is released by subsequent reactions of the free phosphate group.
Hydrolysis also plays a vital role in breaking down food into easily absorbed nutrients. Most organic compounds in food do not react readily with water, and a catalyst is usually required to enable these processes to take place. The organic catalysts that help with reactions in living organisms are known as enzymes. In the body, enzymes such as lipases, carbohydrases and proteases catalyze the reactions of fats, carbohydrates and proteins with water.
An example of hydrolysis is the breakdown of starch, which is catalyzed by the enzyme amylase. Starch is broken down into smaller molecules, which consist of the sugar known as maltose. Maltose can then be further broken down into glucose molecules, under the influence of the maltase enzyme. In each case, water takes part in the process, splitting and adding a hydroxyl group and a hydrogen ion to the new molecules formed on each side of the broken bond.
Industry
Many industrial processes require the hydrolysis of various substances to create useful products. Often, though, the raw materials for these processes don’t react easily with water molecules, so the reactions are aided by a variety of means, such as high pressure, high temperatures, and catalysts. Laboratory hydrolysis usually requires the use of a catalyst, which is typically a strong acid or alkali.
Hydrolysis has been used for a long time in soap making. During this process, known as saponification, the fat is hydrolysed in a reaction with water and the strong alkali, sodium hydroxide. The reaction produces fatty acid salts, commonly known as soap. Saponification sometimes occurs in old oil paintings when the fatty acids in the oil paint react with the metals in the paint pigments. This can cause white deposits and lumps to form on the surface of paintings, although it is not known why this only occurs on some works of art and not others.
Weathering
Hydrolysis is an important process in rock weathering. Various silicate minerals, such as feldspar, undergo slow hydrolysis reactions with water, forming clay and silt, along with soluble compounds. This process is important in forming soils and making essential minerals available to plants.
