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what is scum ?how it is formed?

Scum is basically a stivky white substance which is insoluble in water. It mainly formed due to the reaction of magnesium and calcium ions with the sodium and potaasium salts of carboxylic acids.
when this reaction occurs,an insolube white precipitate is formed which is commonly called as scum.
Scum is normally formed in hard water as it contains magnesium ions or calcium ions, which on reaction with soap forms calcium stearate or magnesium stearate.
The calcium or magnesium stearate  is a white precipitate and commonly known as scum.
2C17 H35 COO- + Ca2+ → Ca ( C17 H35 COO- )2

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Hard water contain Mg and Ca salts and they contain Mg+ and Ca+ ions. We know that soap is Sodium and potassium salts of long chain fatty acids. When hard water is treated with soap , then Mg+ and Ca+ ions reacts with soap to form Magnesium and calcium salts of fatty acid which are insoluble in water and often regarded as scum. Scum is nothing but Mg and Ca salts of fatty acid.

Scum is formed when soap is used with hard water. This is because hard water contains salts of calcium and magnesium. When soap is added to hard water, it reacts with these salts to form scum.

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Soap scum is an informal term for the white solid that results from the addition of soap to hard water. Hard water contains calcium or magnesium ions, which react with the fatty acid component of soap to give what are technically called lime soaps:

2 C17H35COO-Na+ + Ca2+ → (C17H35COO)2Ca + 2 Na+

In this reaction, the sodium ion in soap is replaced by calcium ions.

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Soap does not give foam easily with hard water. Hard water contains calcium and magnesium salts. When soap comes in contact with hard water, these ions form calcium and magnesium salts of fatty acids which are insoluble in water.These calcium or magnesium salts precipitate out in the form of scum.

Sodium Stearate (soap)+ Hard Water ----- Calcium Stearate (scum)+ Magnesium Stearate

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Scum is the insoluble precipitate.

When soap is used for washing clothes with hard water, a large amount of soap is wasted in reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called Scum, before it can be used for real purpose of washing.

The Scumor curdy precipitate) formed by the action of hard water on soap, stticks to the clothes being washed and interferes with the cleaning ability , and makes cleaning difficult.

Hope it hellps :)

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okkkk....i got it!!!!!

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