Hard and soft waterPrint
Water in different parts of the UK varies in the amount of dissolved mineral ions it contains. This determines whether it is hard or soft water. There are advantages and disadvantages to each, but the damage that can be caused to water pipes and appliances by hard water means that water may need to be softened.
Rainwater is naturally weakly acidic [acidic: Having the properties of an acid, such as a pH below 7.] because it contains carbonic acid, formed by the reaction between water and carbon dioxide in the atmosphere. When the rain falls, it flows over rocks or soaks into the ground and then passes through layers of rock. Compounds [compound: A substance formed by the chemical union (involving bond formation) of two or more elements.] from the rocks dissolve into the water.
Hard water [hard water: Water, containing magnesium ions and calcium ions, that does not easily form lather with soap.] contains dissolved compounds, usually calcium or magnesium compounds. For example, limestone contains calcium carbonate, CaCO3. Carbonic acid in rainwater reacts with this to produce soluble calcium hydrogencarbonate:
carbonic acid + calcium carbonate → calcium hydrogencarbonate
H2CO3(aq) + CaCO3(s) → Ca(HCO3)2(aq)
The presence of calcium ions [ion: The charged particle formed when an atom, or a group of atoms, lose or gain electrons. Ion charge helps determine a substance's acidity or alkalinity.] and magnesium ions in the water makes it hard. Soft water [soft water: Water that readily forms lather with soap.] readily forms lather with soap, but it is more difficult to form lather with hard water. The dissolved calcium ions and magnesium ions in hard water react with the soap to form scum [scum: An insoluble precipitate that forms with soap and hard water.] , so more soap is needed. Soapless detergents do not form scum with hard water.
The types of rocks found in different regions determines how hard or soft the water will be.
The water in some parts of the country is soft because it has low levels of dissolved calcium and magnesium compounds, while the water in other parts of the country is hard because it has higher levels of dissolved calcium and magnesium compounds.
There are varying degrees of hardness in water - from slightly hard to very hard.
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