Question

Q. The mole fraction of water in an
aqueous solution of NaCl is 0.75. The
molality of the solution is
(a) 6.2 m (b) 9.25 m
(c) 18.5 m (d) 37 m

Answer 1

Answer:Mole fraction of H²O in solution =0.75

∴   Mole fraction of solute in solution =1−0.75=0.25

Hence each mole of solution, 0.25 mole of solute is dissolved.

0.75 mole of water =18×0.75=13.5gm=0.0135Kg

Molality (m)= no. of moles of solute / mass of solvent

                     =   0.25 /0.0135

                     =18.5m

∴   Correct answer is c.

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