A descaling agent or chemical descaler is a liquid

chemical substance A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wit ...

used to remove

limescale Limescale is a hard, chalky deposit, consisting mainly of calcium carbonate (CaCO3). It often builds up inside kettles, boilers, and pipework, especially that for hot water. It is also often found as a similar deposit on the inner surfaces of ol ...

from metal surfaces in contact with hot water, such as in boilers, water heaters, and kettles. Limescale is either white or brown in colour due to the presence of

iron compounds Iron shows the characteristic chemical properties of the transition metals, namely the ability to form variable oxidation states differing by steps of one and a very large coordination and organometallic chemistry: indeed, it was the discovery o ...

. Glass surfaces may also exhibit scaling stains, as can many ceramic surfaces present in bathrooms and kitchen, and descaling agents can be used safely to remove those stains without affecting the substrate since both ceramics and glass are unreactive to most acids.

Action

Descaling agents are typically

acidic In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...

compounds such as

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...

that react with the calcium carbonate and

magnesium carbonate Magnesium carbonate, (archaic name magnesia alba), is an inorganic salt that is a colourless or white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals. Forms The most common magnesium carbonate forms are ...

compounds present in the scale, producing

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

gas and a soluble salt. CaCO₃(s) + 2H⁺(aq) → Ca²⁺(aq) + CO₂(g) + H₂O(l) MgCO₃(s) + 2H⁺(aq) → Mg²⁺(aq) + CO₂(g) + H₂O(l) Strongly acidic descaling agents are usually

corrosive A corrosive substance is one that will damage or destroy other substances with which it comes into contact by means of a chemical reaction. Etymology The word ''corrosive'' is derived from the Latin verb ''corrodere'', which means ''to gnaw'', ...

to the eyes and skin, and can also attack and degrade clothing fibres, so appropriate protection such as rubber gloves and

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...

aprons should be used in cleaning operations.

Acids used

Notable descaling agents include

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main componen ...

citric acid Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in ...

glycolic acid Glycolic acid (or hydroxyacetic acid; chemical formula HOCH2CO2H) is a colorless, odorless and hygroscopic crystalline solid, highly soluble in water. It is used in various skin-care products. Glycolic acid is widespread in nature. A glycolate (s ...

formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Est ...

lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as nat ...

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...

, sulfamic acid and

. The calcium salts are soluble and thus washed away during dissolution or

Solvation Solvation (or dissolution) describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of t ...

. The speed of the descaling action depends on the

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', ''number concentration'', ...

and

acidity In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...

or pH of the solution provided. Hydrochloric acid is much stronger than acetic acid for example, so tends to remove scale faster. Weak acids such as acetic or citric acids may be preferred however, where damage to the substrate is to be minimised. There are many companies offering inhibited or " buffered" acids that inhibit the corrosive effect of the acids on various materials. Typically about a 10% concentration of hydrochloric acid with a corrosion inhibitor and some added penetrating and wetting agents added. This allows for a better cleaning of machinery and especially

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...

s because often the scale is mixed up with

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

and other contaminants. These additives reduce the corrosion on the metals and cut through and loosen up these other materials mixed with the scale for faster and more thorough cleaning.

References

{{Reflist Chemical process engineering Plumbing Heating, ventilation, and air conditioning

Action

Acids used

See also

References