Question

A drop of olive oil of radius 0.25 mm spreads into a circular film of radius 10 cm on the water surface. Estimate the size of molecule of oleic acid.

Answer 1

Here,`r = 0.25 mm = 0.25xx10^(-3)m, `
`R =10cm = 10^(-1) m`
Thickness of oile film ` = ("volume of oil drop")/("area of the film")`
`((4)/(3)pir^3)/(piR^2) = (4)/(3) (r^3)/(R^2) = (4)/(3)(0.25xx10^(-3))^3/((10 ^(-1))^2)`
`= 2.08xx 10 ^(-9)m`
If we assume the oil film to be one molecule
thick, then size of molecule of oleic acid
`= 2.08xx10^(-9) m`