Chemistry Unit 3

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  • Created by: R Butler
  • Created on: 02-05-13 21:04

C3.2 Hard Water

Hard water is water which is difficult to form a lather with a soap in. This is because it contains dissolved magnesium and/or calcium ions which react with the soap to form scum.

How hard water forms:

i) Magnesium and calcium ions get into the water as rivers or streams run over magnesium/calcium compounds and the compunds dissolve, eg. Gypsum - calcium sulphate

ii) Limestone causes hardness in water as calcium carbonate, although it is insoluble in water, as rain falls caron dioxide dissolves in the rain, making it slightly acidic, this slightly acidic water runs into rivers and reacts with calcium carbonate to form calcium hydrogencarbonate, which is soluble in water. Therefore Ca2+ ions get into the water.

Soaps chemical name is sodium stearate.

In hard water, some soap is watsed as it is reacted with the calcium and/or magnesium ions to form insoluble salts (scum). Only once the scum is formed can the soap lather.

One type of hard water can also form scale, or limescale as its better known. This insoluble solid forms when hard water is heated. This scale can block pipes and reduce fficiency of appliances.

Despite all these disadvantages, hard water does have its benefits. The Ca2+ ions in hard water can help the growth of strong teeth and bones, and there is…

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