Chemistry of water -Part 7-

Water hardness and softening:

Hard water is natural water that contains calcium ions (as well as magnesium ions and, in some cases, iron ions). Before using this type of water in industry or at home, it must first be treated.

A tub faucet with built-up calcification from hard water in Southern Arizona- Wikipedia

Water hardness comes in two types:

A - Temporary or carbonic hardness:
Along with the mineral ions we previously mentioned, it is caused by the presence of carbonate ions in the water.

b- Permanent or non-carbonated hardness:
Specifically, the presence of sulfate and chloride ions is what causes it.

Water's hardness can be determined by how it reacts with regular soap, which is made of fatty acid salts in either sodium or potassium. In water, soap breaks down into negative ions like oleate (C18H33O2-), which combine with calcium ions to form insoluble calcium oleate:

Ca++ + 2C18H33O2- ==== Ca (C18H33O2)2 (s)

This reaction wastes the soap, and the precipitate that forms is deposited on the fabric fibers, carrying additional soap with it and preventing the transfer of dirt from the fabric to the water.

Additionally, hard water has the negative effect of causing the precipitation of calcium carbonate and calcium sulfate in pipes, which occurs in boilers, because they are poor heat transfer materials, the local increase in heat results in a reduction in the boiler's thermal efficiency.

• Temporary hardness, or carbonate hardness, can be eliminated by boiling and filtering water, which is why it is so called; permanent hardness, on the other hand, cannot be eliminated by boiling.

References:

• Kada, Imene- Double ionisation de la molécule d’eau par impact d’électrons- Phd thesis

• Pezzella, Marco. Molecular dynamics at water interfaces: from astrophysical to biochemical applications. 2020, Phd Thesis no:13717, University of Basel, Faculty of Science.

• [General and inorganic chemistry book- M. Shkhashirou- H. Birqdad- Y. Qodsi- University publications. Algeria]

• Berend Ensing; geboren te Delfzijl- Chemistry in Water. Phd Thesis. University of Amsterdam- 2003

• [AQUAPROX- Livre: Traitement des eaux de refroidissement. Imprimé en France par EMD S.A.S- 53110 Lassay-les-Chateaux. N° d'imprimeur: 15566- Dépot légal: juin 2006. N° 842- Cyclus print 90°]