Soap may be represented by the formula `RCOO^(-)Na^(+)` where R is an alkyl group which represents long chain of carbon with fifteen or more atoms.Now, oil drops containing dirt particles and water donot mix. Soap helpsin their mixing by reducing interfacial tension or friction.Actually it forms a sort of bridge between oil drops and water in which the alkyl portion (hydrophobic end) points towards oil drop while other portion COONa (hydrophilic acid) is directed towards water. this is known as micelle formation. thus, soap helps in the formation of a stable emulsion between oil and water.Ethanol and other similar solvents which are of organic nature, donot help in micelle formation becasue soap is soluble in them.