A descaling agent or chemical descaler is a liquid chemical substance used to remove limescale from metal surfaces in contact with hot water, such as in boilers,

water heaters Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a s ...

, and kettles. Limescale is either white or brown in colour due to the presence of iron compounds. 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 compounds such as hydrochloric acid 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 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 to the eyes and skin, and can also attack and degrade clothing fibres, so appropriate protection such as

rubber gloves A rubber glove is a glove made out of natural rubber or Synthetic rubber. The term ‘rubber’ refers to durable, waterproof and elastic material made from natural or synthetic latex. Rubber gloves can be unsupported (rubber only) or supported ( ...

and plastic 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 component ...

, citric acid, glycolic acid,

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. Es ...

, lactic acid, phosphoric acid, sulfamic acid and hydrochloric acid. The calcium salts are soluble and thus washed away during dissolution or Solvation. The speed of the descaling action depends on the concentration and acidity 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 exchangers because often the scale is mixed up with silica 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