The qualitative sketches I, II and III given below show the variation of surface tension with molar concentration of three different aqueous solution of KCl, CH 3 OH and CH 3 (CH 2 ) 11 OSO 3 – Na + at room temperature. The correct assignment of the sketches is:
Text Solution
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Impurities affect surface tension appreciably. It is observed that impurities which tend to concentrate on surface of liquids, compared to its bulk lower the surface tension.
Substance like detergents, soaps (CH 3 (CH 2 ) 11 SO 3 – Na + ) decreases the surface tension sharply.
Those like alcohol (eg. –CH 3 OH, C 2 H 5 OH) lower the surface tension slightly. This can also be related to the fact that CH 3 OH has smaller dielectric constant. Dielectric constant is directly proportional to surface tension. So, on adding CH 3 OH in water, overall dielectric constant decreases and surface tension decreases.
Inorganic impurities present in bulk of a liquid such as KCl tend to increase the surface tenstion of water.
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