Question
Why does hard water not form lather with soap?
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Answer
Soap is sodium or potassium salt of fatty acid. it is made up when alkali reacts with fatty acids. hardness of water is due to calcium and magnesium ions. sodium salts dissolve in water and hence lather is formed when soap is added to hard water, calcium and magnesium ions replaces sodium (or potassium) ions in the salt (soap) and gets precipitated hence lather formation is hindered.
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