Limescale
Encyclopedia
Limescale is the hard, off-white, chalky deposit found in kettles, hot-water boilers and the inside of inadequately maintained hot-water central heating systems. It is also often found as a similar deposit on the inner surface of old pipes and other surfaces where "hard water
" has evaporated.
These types of limescale differ slightly due to their origins.
The type found deposited on the heating elements of water heaters etc. has a main component of calcium carbonate
, precipitated out of the (hot) water. Hard water
contains calcium
(and often magnesium
) bicarbonate
and/or similar salts.
Calcium bicarbonate
is soluble in water, however at temperatures above 70 °C (158 °F) the soluble bicarbonate is converted to poorly-soluble carbonate, leading to deposits in places where water is heated. Local boiling “hot spots” can also occur when water is heated, resulting in the concentration and deposition of salts from the water.
Calcium cations from hard water can also combine with soap
, which would normally dissolve in soft water. This combination often forms scum which precipitates out in a thin film on the interior surfaces of baths, sinks, and drainage pipes. Soap usually contains salts of anions from neutralized fatty acid
s or similar chemical compound
s. The calcium salts of these anions are less soluble in water.
The type found on air-dried cooking utensils, dripping taps and bathroom tiling consists of calcium carbonate mixed with all the other salts that had been dissolved in the water, prior to evaporation
.
It can also be found on taps where hard water
has been continually running through and has deposited calcium carbonate
. This can be a help to start with by protecting the inside of the tap, but can build up, reducing water flow and can eventually block the tap.
In kettles, limescale acts as an insulator, impairing heat transfer. Additionally, it can damage the heating element, which overheats due to accruing limescale.
to water, which act as chelating agents (it binds to the metal ions, inactivating them). Adding some carbonated water with low amounts of dissolved Ca and Mg cations (the cheapest mineral water is usually the best for this purpose) also works by dissolving carbonate again as bicarbonate. In kettles and coffee machines the water will not boil long enough for all the carbonate to precipitate out, and the bicarbonate will stay dissolved in the water.
Alternatively, one may use a ball of steel wire, whose surface area attracts much of the limescale, to reduce the accumulation. The ball can then be cleaned coarsely via squeezing (breaking off the brittle limescale), or finely via a descaling agent.
It can also be removed via a scouring pad
, though this may damage the underlying surface.
Hard water
Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...
" has evaporated.
These types of limescale differ slightly due to their origins.
The type found deposited on the heating elements of water heaters etc. has a main component of calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, precipitated out of the (hot) water. Hard water
Hard water
Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...
contains calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
(and often magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
) bicarbonate
Bicarbonate
In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
and/or similar salts.
Calcium bicarbonate
Calcium bicarbonate
Calcium bicarbonate , also called calcium hydrogencarbonate, does not refer to a known solid compound; it exists only in aqueous solution containing the calcium , bicarbonate , and carbonate ions, together with dissolved carbon dioxide...
is soluble in water, however at temperatures above 70 °C (158 °F) the soluble bicarbonate is converted to poorly-soluble carbonate, leading to deposits in places where water is heated. Local boiling “hot spots” can also occur when water is heated, resulting in the concentration and deposition of salts from the water.
Calcium cations from hard water can also combine with soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...
, which would normally dissolve in soft water. This combination often forms scum which precipitates out in a thin film on the interior surfaces of baths, sinks, and drainage pipes. Soap usually contains salts of anions from neutralized fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s or similar chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s. The calcium salts of these anions are less soluble in water.
The type found on air-dried cooking utensils, dripping taps and bathroom tiling consists of calcium carbonate mixed with all the other salts that had been dissolved in the water, prior to evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
.
It can also be found on taps where hard water
Hard water
Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...
has been continually running through and has deposited calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
. This can be a help to start with by protecting the inside of the tap, but can build up, reducing water flow and can eventually block the tap.
How to make Limescale occur
Boil hard water in a pan. After water begins to bubble, turn off the heat and remove the water. You will get limescale in the pan (because boiling hard water will make water soft but leave limescale in the pan).Effects
Other than being unsightly and harder to clean, limescale can impair the operation of various components or damage them.In kettles, limescale acts as an insulator, impairing heat transfer. Additionally, it can damage the heating element, which overheats due to accruing limescale.
Prevention
In kettles, one can add crystals of citric acidCitric acid
Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...
to water, which act as chelating agents (it binds to the metal ions, inactivating them). Adding some carbonated water with low amounts of dissolved Ca and Mg cations (the cheapest mineral water is usually the best for this purpose) also works by dissolving carbonate again as bicarbonate. In kettles and coffee machines the water will not boil long enough for all the carbonate to precipitate out, and the bicarbonate will stay dissolved in the water.
Alternatively, one may use a ball of steel wire, whose surface area attracts much of the limescale, to reduce the accumulation. The ball can then be cleaned coarsely via squeezing (breaking off the brittle limescale), or finely via a descaling agent.
Treatment
Limescale can be removed using various descaling agents and penetrating tools. Principally these are acids which react to form more soluble products.It can also be removed via a scouring pad
Scouring pad
A scouring pad or scourer is a small pad of metal or plastic mesh used for scouring a surface. Some scouring pads have one side made of a soft sponge-like material and the other is the aforementioned plastic mesh.-History:...
, though this may damage the underlying surface.
See also
- FoulingFoulingFouling refers to the accumulation of unwanted material on solid surfaces, most often in an aquatic environment. The fouling material can consist of either living organisms or a non-living substance...
- Descaling agentDescaling agentAn anti-scaling agent, also known as descaling agent, anti-limestone, anti-limescale, anti-lime or anti-scale are preparations to prevent the buildup or to remove limescale and fouling...
- Water softener
- Hard waterHard waterHard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...
- Magnetic water treatmentMagnetic water treatmentMagnetic Water treatment usually by the application of a changing Magnetic flux is a proposed method of water softening The flux change may be deliberately caused by an electromagnet or the result of water flowing near a permanent magnet, usually in a pipe surrounded by the magnetic water treatment...
- LimestoneLimestoneLimestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
- Calcium carbonateCalcium carbonateCalcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...