Class 10 Science - Chapter Carbon and Its Compound NCERT Solutions | Explain the formation of scum when hard

Welcome to the NCERT Solutions for Class 10th Science - Chapter Carbon and Its Compound. This page offers a step-by-step solution to the specific question from Exercise 6, Question 10: explain the formation of scum when hard water is t....
Question 10

Explain the formation of scum when hard water is treated with soap.

Answer

Soap does not work properly in hard water. A soap is a sodium or potassium salt of long chain carboxylic acid. Hard water contains salts of calcium and magnesium. When soap is added to hard water, sodium and potassium ions present in soap displace calcium or magnesium ions from the water molecules forming an insoluble substance called scum. A lot of soap is wasted in the process.

For example:

Sodium Stearate + Calcium chloride → Sodium chloride + Calcium Stearate (scum)

Formation of scum hinders the formation of foam, so soap is thus unable to clean in hard water.

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