Question

10 drops of oleic acid solution of concentration 1/400 cm^3 per cm^3 of alcohol are dropped on a water surface. the circular​ film thus produced has radius 10cm. find the molecular size of oleic acid if the radius of each drop is 1.4mm

Answer 1

Oleic acid is soluble in alcohol but insoluble in water. (b) Lycopodium powder spreads on the entire surface of water. When a drop of the solution of oleic acid in the solution spreads on water surface as it does not dissolve in water. The drop pushed the lycopodium powder particles away and creates a circular area where it falls, thus enabling us to measure the area where oleic acid spreads. (c) Since 20 mL (1 mL oleic acid + 19 mL alcohol) contains 1 mL of oleic acid, oleic acid in each mL of the solution =120mL. Further, as this 1 mL is diluted to 20 mL by adding alcohol, oleic acid in each mL of prepared solution. =(120mL)20 =(1400)mL (d) By means of a burette (to allow the solution to trickle out in drops so that these can be counted) and measuring their volume with a measuring cylinder, the volume of n drops can be calculated. (e) If n is the number of drops in 1mL of the solutions, volume of oleic acid in one drop =[1400]mLn =(1400n)mL