Find the average molecular mass of starch given that an aqueous solution of10g/c of starch has an osmatic pressure `5 xx 10^(-3)` atm at `25^(@)C` what is the approximate number of glucose units in this sample of starch

Options

A. 312
B. 302
C. 322
D. 332

Answer

B

Explanation

Concentration of glucose `= C = (10^(4)gm)/(M), pi= CRT, 5 xx 10^(-3) = (10^(4))/(M), x 0.0821 xx 298 :. M = 4.893 xx 10^(7)`
Number of glucose units `= (4.893 xx 10^(7))/(162) = 302` (Note : MW of glucose is taken as 162 since in the formation of starch `H_(2)O` is lost `180-18 = 162`)