Surface tension of water+alcohol

[toni_2374]

Homework Statement

explain the change in surface tension of mixture of water+alcohol(n-octanol,n-heptanol,n-butanol)? discuss their degree of their solubility in water and this affect to surface tension?

Homework Equations

L=SURFACE CONCENTRATION
δ=SURFACE TENSSION
C=CONCENTRATION OF ALCOHOL IN WATER
L=(1/RT)*∂δ/∂ln(c)

The Attempt at a Solution

If a alcohol is soluble a little in water it can change surface tension so much if a little amount of alcohol is added.

 

[Valkarie]

As alcohols are more soluble in water, the surface tension decreases. This is because the alcohol molecules form a monolayer on the surface of the liquid and the molecules of water are displaced by the alcohol molecules. The decrease in surface tension is due to the lower surface concentration of water molecules and the higher surface concentration of alcohol molecules. To explain the change in surface tension of mixture of water and alcohol, it can be expressed in terms of the Langmuir equation, which states that the surface tension (δ) is dependent on the surface concentration (L) as follows: δ = RTL / (1 + C/L) where R is the gas constant, T is the temperature and C is the concentration of alcohol in the water. The degree of solubility of an alcohol affects the surface concentration of the molecules at the surface of the liquid. As the solubility of an alcohol increases, the surface concentration of the molecules also increases, resulting in a decrease in surface tension. For example, n-butanol has a higher solubility in water compared to n-octanol and n-heptanol, so when n-butanol is added to water, the surface tension will decrease more than when n-octanol or n-heptanol are added.