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

Cheers .concentration given must be multiplied with the volume of oleic acid

Answer 2

Hello Dear.

We know, the Shape of the one Drops is Spherical in shape.

Radius of the Drop = 1.4 mm.
 = 0.14 cm.

∴ Volume of the Drop = (4/3)π r³
     = (4/3) × (22/7) × (0.14)³
     = (241472 × 10⁻⁶) ÷ 21

Volume of the 10 Drop of 1/400 cm³ Concentration/cm³ 
= Volume of 1 Drop × 10 × 1/400 
= (241472 × 10⁻⁶) ÷ (21 × 400)
= (603.68 × 10⁻⁶) ÷ 21
= 603.68/21000000  cm³


Radius of the Circular Film = 10 cm.

∵ Area = π r²
            = (22/7) × (10)²
            = 2200/7 cm²


Now,
Molecular Size or Thickness = Volume of one drop/Area of the Film.

   = $\frac{ \frac{603.68}{21000000} }{ \frac{2200}{7} }$
   =  (603.68 × 7) ÷ (21 ×  10⁶ × 2200)
   =  (4225.76 × 10⁻⁸) ÷ 462
   = 9.1467 × 10⁻⁸ cm

Thus, the the Thickness or the Molecular size of drop of Oliec Acid is 9.1467× 10⁻⁸ cm.


Hope it helps.