A 25 % solution of cane-sugar (molar mass =342 ~g ~mol ⁻¹ ) is isotonic with 5 % solution of a substance A . Then find the molecular weight of A .

Step-by-step solution

Two solutions are isotonic when they have the same osmotic pressure. It is only possible when they have same molar concentration. A 25 % solution of cane-sugar means 100 ~g of solution contain 25 ~g of cane-sugar. For dilute solution 100 ~g is approximately equal to 100 ~mL . Molarity of cane-sugar aligned & = Number of mole of cane-sugar Volume (in L) & = 25 ~g 342 ~g / mol 100 ~mL 1000 ~mL & =0.7309 M ...(i) aligned Now, 5 % solution of substance A means 100 ~g of the solution contain 5 ~g of substance A . For di