The molar concentrations of two individual surfactants required to yicld a surface tension value of 36 dynes/cm in aqueous solution are 2.6 x 10-3 and 1.15 x 10-), respectively. The total molar surfactant concentration required to yield a surface tension of 36 dynes/cm is 6.2 x 10 for a mixture of the two surfactants in which the mole fraction of the first surfactant (on a surfactant- only basis) is 0.41. Calculate the value of Xi, the mole fraction of surfactant 1 in the total surfactant at the aqucous solution air interface for this mixturc. Solution The stronger the intermolecular forces of a liquid, the stronger its surface tension. Normally, the concentration of whatever substances H2O contains has nothing to do with its surface tension. An exception is the concentration of surfactants. The most commonly known surfactant is soap, i.e. sodium stearate. The more sodium stearate molecules present in a certain amount of H2O, the lower the surface tension. For other liquids such as some organic solvents, there are no â€œoil surfactantsâ€, and whatever substance the solvent holds probably wonâ€™t affect the strength of intermolecular forces between solvent particles, so the is no relation between surface tension of a glass of oil and the concentration of a certain substance in it .