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A descaler (also: limescale remover ) is a chemical cleaning agent used to remove limescale deposits such as scale . In the household, acetic acid , citric acid and amidosulphonic acid are used in particular , as well as products that contain these substances.

Formation of lime

Lime CaCO 3 (Ca 2+ and CO 3 2− ) is formed from tap water at elevated temperatures ( e.g. in kettles). The water-soluble calcium hydrogen carbonate Ca (HCO 3 ) 2 contained in tap water is converted into water-insoluble lime (chemical name: calcium carbonate), which settles on the walls or heating elements of the stove and increasingly hinders the transfer of heat.


The solubility of CaCO 3 is increased by adding acid . The protonated water molecules contained in the acidic solution (oxonium ions, H 3 O + ) give off protons to the carbonate ion (CO 3 2– ). This reacts again to form carbonic acid (H 2 CO 3 ), which instantly breaks down into water (H 2 O) and gaseous carbon dioxide (CO 2 ). The calcium ions (Ca 2+ ) together with the anion of the acid used form a water-soluble salt.

Reaction equation

Dissolving the lime with acetic acid :

Acetic acid reacts with insoluble lime (CaCO 3 ) to form water-soluble calcium acetate [dissociates into calcium ions (Ca 2+ ) and acetate ions (H 3 C-CO 2 - )], gaseous carbon dioxide escapes, which is why it foams.

Dissolving the lime with citric acid :

Instructions for use

Different decalcifying agents are used depending on the application or device.

Acetic acid can corrode metals and damage seals and should therefore only be used for decalcifying devices that are made entirely of stainless steel or other acid-resistant materials and whose seals, if any, can be easily replaced.

When using citric acid , devices with water heating (coffee machine, water heater, kettle, etc.) should not be switched on. Warmed acid dissolves the lime more quickly, but when heated, the lime residue precipitates again and can lead to hard-to-dissolve deposits and blockages. For this reason, cleaning tabs for coffee machines often contain lactic acid .

With sulfamic acid , problems with corrosion or stubborn deposits generally do not occur. It is therefore used in the majority of the commercially available decalcifying agents, which have a wide range of uses.

Limescale deposits on vertical surfaces, such as shower walls, can be removed by cleaning toilet paper (or other soft and absorbent material) with an acid, e.g. B. vinegar essence is soaked and placed on the surfaces to be decalcified. In the case of heavier deposits, the soaked cellulose is left on the surface for several hours or several days and, if necessary, moistened again with water or acid, whereby concentrated acids can also be used here. Protective gloves and glasses must be worn when handling these.

Washing machines and dishwashers do not normally have to be descaled, in spite of claims made by manufacturers of descaling agents to the contrary, as the dishwashing detergents and detergents used contain sufficient water softeners to prevent limescale deposits, even if the dosage is insufficient. A severe underdosing of the detergent would initially lead to so-called fat lice on the laundry (small, gray, greasy stains from lime soap ) before the lime begins to settle on the heating elements.

See also