In the presence of acid, soaps will undergo the reaction shown below. Explain ho

Question

In the presence of acid, soaps will undergo the reaction shown below. Explain how this would affect the ability of soap to act as a cleaning agent if it is used in water that is acidic. A friend lives in an area where the tap water is very hard due to high levels of calcium ion. She notices that a bath soap containing sodium palmitate leaves a heavy film of soap scum on her shower. The chemical reaction below is responsible for this observation. Complete and balance the chemical equation, and explain the source of the soap scum NaO_2C(CH_2)_4CH_3 + CaCl_2 rightarrow

Explanation / Answer

Q1) In presence of acid , the reaction of soap is

RCOONa + H+ --------> RCOOH + Na+

If the water is acidic , it hydrolyses soap to acid , which areinsoluble in water , thus forms a precipitate(scum) .

So the foaming action of soap is decreased.

So soaps are ineffective in acidic water.

Q2) In hard water the hardness is due to dissolved magnesium and calcium ions.

When soap is used in hard water , it forms magnesium and calcium salts of soap, which are insoluble in water unlike sodium salts.

Thus they form scum and soap action is decreased.

2CH3(CH2)14 COONa + Ca+2 ----------> [CH3(CH2)14COO]2 Ca + 2Na+

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