C3.2 Hard and Soft Water

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  • Created by: Curlot
  • Created on: 09-04-14 16:01

Hard Water

How does Hard Water Form?

Most hard water contains dissolved calcium and magnesium ions. These dissolve when a river flows over rocks of these materials. Limestone also causes hardness in water because it is mainly calcium carbonate which is insoluble, however when rain falls carbon dioxide in the air dissolves into it, making that water slightly acidic.

Calcium carbonate reacts with the slightly acidic solution and the calcium hyrdogencarbonate created is soluble in water. Therfore calcium ions get into the water making it hard.

Hard water Vs. Soap

When we have hard water we need to use more soap because before it has removed the dirt some of it is wasted reacting with the calcium and magnesium ions in the water. This forms insoluble salts that appear as scum. Only when all the calcium and magnesium ions have reacted can the soap form a lather.

Sodium Sterate + Calcium Ions-> calcium stearate Precipitate + Na+ ions (soluble in water)


Hard water can also lead to the


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