The mole fraction of water in a solution of HCI is 0.78. Calculate the molality of the solution.

The mole fraction of water in a solution of HCI is 0.78. Calculate the

1.	The mole fraction of water in a solution of HCI is 0.78. Calculate the molality of the solution.
Answer» SOLUTION :Mole fraction of WATER = 0.78 Mole fraction of HCI = `1 - 0.78 = 0.22`. SUPPOSE, the solution contains `n_(1)`moles of HCI and `n_2` moles of water. Therefore, `n_(1)/(n_(1) + n_(2)) = 0.22`……..(i) and `n_(2)/(n_(1) + n_(2)) = 0.78`……...........(ii) DIVIDING eq. (i) by eq. (ii), we have `n_(1)/n_(2) = 0.22/0.78 = 0.28`.............(iii) Since, molality refers to the number of moles of solute dissolved in 1000 g of solvent (water in the present case), `n_(2) = 1000/18 = 55.55` Substituting the value in eq. (iii), we have `n_(1)/55.55 =0.28` or `n_(1) = 0.28 xx 55.55 = 15.55` Hence, the molality of the given solution is 15.55 m.