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Chemistry in Everyday Life — Chemistry STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceChemistryChemistry in Everyday Life3 Marks
Question
Why the soaps do not work in hard water?
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Answer

(i) 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 present in hard water to form a scum, before it can be used for the real purpose of washing.
$\underset{\text { Soap (in hard water) }}{ C _{17} H _{25} COONa + CaCl _2} \longrightarrow 2 NaCl +\underset{\text { Insoluble calcium stearate (Soap) }}{\left( C _{17} H _{35} COO \right)_2 Ca }$
(ii) The scum formed by the action of hard water on soap sticks to the clothes being washed and interferes with the cleaning ability of the additional soap. Thus soaps do not work in hard water.

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