Question

 A burette is filled with oleic acid drop upto the 15.5cm³ ark. After 50 drops of the oil were let out of the burette the level of the oil dropped to 22.5cm³.

1. Determine the volume of one drop of the oleic oil. 
2. One drop of the oleic oil is carefully introduced onto a clean surface of a trough. It spread to a patch. Determine the thickness of each oleic oil molecules in metres. (Assuming the radius of drop = radius of patch). 
3. State two assumptions made in part (b) above. 

Answer 1

1. 50 drops = 22.5
                 −15.5 
                     7.0
   1 drop = 7.0
                 50   
             = 0.14cm³     
2. Vol of the drop = vol of the patch
   ∴ ⁴/₃πr³ = πr²×t
   But ⁴/₃πr³=0.14
   r³ = 0.14×3
            4π
   
   = 0.322 cm
   Hence 0.14 = π x 0.322² x t 
   t =    0.14     
        π x 0.3222
   = 0.4298 cm 
3.   
   1. Oil spread to one molecule thick.  
   2. No evaporation took place.