Temporary water hardness

What is meant by the term temporary water hardness, where it is significant, and how to determine the temporary water hardness is explained in this article.

Temporary and permanent water hardness

The temporary water hardness indicates the content of water in bicarbonate (HCO3 +), CO3- and OH-. It is therefore called carbonate hardness.

In contrast, stands the permanent water hardness. All alkaline earth metals dissolved in the water, which is not bound in the form of bicarbonate or magnesium carbonate, count to non-carbonate hardness or permanent water hardness.

Both together make up the total water hardness. It alone indicates the concentration in which salts of the alkaline earth metals are dissolved in the water.

Kalkkohlensäure balance

The calcium ions are balanced by dissolved CO2 in the water. As a result, lime can neither be eliminated from the water, nor lime can be absorbed.

If CO2 is removed from the water, limescale is separated. Deposits form in the form of dolomite or calcite - or the so-called scale. These deposits are very difficult to dissolve.

The balance between calcium and carbon dioxide is also temperature dependent. When the water is heated, lime is also precipitated.

Term temporary water hardness

The term "temporary water hardness" derives from the fact that the lime components bound by HCO3, CO3 and OH ions are precipitated on warming of the water and also on CO2 removal.

So they are not permanently dissolved in the water, but only temporarily, as long as no increase in temperature takes place, and as long as no CO2 is withdrawn. Therefore the term temporary or temporary water hardness.

Protection against precipitation

Especially in washing machines, it is important to avoid precipitation of lime when warming the water as possible.

The advertised for many years Calgon, which is to avoid calcification of the washing machine, contains for it synthetic zeolites. This substance forms a lattice structure and reduces water hardness by functioning like an ion exchanger.

Synthetic zeolites release Na + ions, taking up Ca + and Mg2 + ions in the lattice structure.

Tips & Tricks

A reduction in water hardness is also possible with other methods - there are different water softening systems.

Video Board: Class 11 Chemistry: How to remove temporary hardness of water? | Removal of hardness from water