Question

If the mole fraction of urea in water is 0.15 then
molality of urea in the solution will be
(1) 3.4 m (2) 2.5 m
(3) 7.5 m (4) 9.8 m

Answer 1

Answer:

9.8 m

STEP BY STEP EXPLANATION

➡ GIVEN :- mole fraction of urea in the water is 0.15

mole fraction of water

= 1 - mole fraction of urea

= 1 - 0.15

= 0.85

Thus, no. of moles of urea in the solution will be =   0.15

the number of moles of water in the solution will be =.85

So, mass of urea present in solution will be = number of moles of urea X molar mass of urea

= 0.15 X 60

= 9g

Similarly mass of water present in the solution will be = number of moles of water X molar mass of water

= 0.85 X 18 = 15.3g

Now, molality of a solution is given by the following relation

molality = number of moles of solute / Mass of solvent (in Kg)

So, molality of urea solution will be = 0.15 / 0.0153

=9.8 m

HOPE IT HELPED

Answer 2

Answer:

The molality of urea in the solution will be equal to 9.8m.

Therefore the option (4) is correct.

Explanation:

Given: In water the mole fraction of urea $x_{A}=0.15$

Then the mole fraction of water, $x_{B}=1-x_{A}$

                                                     $x_{B}=1-0.15\\x_{B}=0.85$

Number of moles of urea $n_{A}=0.15$

Number of moles of water, $n_{B}=0.85mol$

Mass of urea =(No. moles of urea)(Molar mass)

                     $=0.15*60\\=9g$

Mass of water in solution $=0.85*18=15.3g$

Molality of solution = (no. of moles of urea)/(mass of solvent in kg)

Molality of urea in solution $=\frac{0.15}{15.3*10^{-3}}=9.8m$