Asked by yaminisanwal | 19th Aug, 2008, 09:35: PM

Expert Answer:

When soap is added to water, the ionic-salt end of the molecule is attracted to water and dissolved in it.

The non-polar hydrocarbon end of the soap molecule is repelled by water The soap molecules "stand up" on the surface as the polar carboxyl salt end is attracted to the polar water.

The non-polar hydrocarbon tails are repelled by the water, which makes them appear to stand up.

The oil or grease is a pure hydrocarbon so it is non-polar. The non-polar hydrocarbon tail of the soap dissolves into the oil.

  That leaves the polar carboxylate ion of the soap molecules are sticking out of the oil droplets, the surface of each oil droplet is negatively charged.

As a result, the oil droplets repel each other and remain suspended in solution (this is called an emulsion) to be washed away by a stream of water.

Answered by  | 20th Aug, 2008, 07:37: AM

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