Question

10 drops of an oleic acid solution of concentration 1 by 400 cm cube per centimetre cube alcohol are dropped on water surface the circular film does produced has radius 10 cm find the molecular size of oleic acid if the radius of each drop is 1.4 mm

Answer 1

circular film : r =10cm   n=no of drops, concentration=1/400 cm³,
t = nv/400A

Area(A)  = πr^2×400
         =π×(10)^2×400
     A  = 4×10^4 πcm²

Volume of ten drops =4/3πr³
                               =4/3π×(1.4)³×10 mm³            [r=1.4]
                               =4/3π×2.744×10 mm³
                               =4/3π×2744×10^-3×10 mm³
                               =4/3π×2744×10^-2 mm³
                                =10976/3π×10²×10^-3 cm³
                    nV            =10976/3π×10^-5 cm³

  Molecular size =nV/400A 
                         =10976π×10^-5cm³/3/4×10^4πcm³
                         =10976π×10^-5cm³/3×1/4×10^4πcm³
                         =9.15×10^-9m it is approx ans
                               

Answer 2

Answer:9.11*10 to the power - 7cm

Explanation: