a solution containing 5g of non -volatil solute in 50g of water bolis at 373 52k. calculate the molar mass of the solute .(kb for water is 0.52k kg/mol)
Answers
Answer:
As we know that, depression in boiling point,
ΔTb =kbm
where,
ΔT
b
= Elevation in boiling point = 0.52
k
b
= molal elevation of boiling point = 0.52
m = molality of solution = ?
∴0.52=0.52×m
⇒m=1
As,
m=
Kg of solvent
moles of solute
=1
⇒ As the molality is 1, it signifies that 1 mole of urea is present in 1 kg of water.
∴ no. of moles of water in the solution =
18
1000
=55.55;(∵ 18 is the molar mass of water)
As we know,
mole fraction of solute or solvent in the solution =
total no. of moles of solution
no. of moles of solute or solvent
∴ mole fraction of urea in water =
total no. of moles
no. of moles of urea in the solution
⇒ mole fraction of urea in water =
1+55.55
1
=
56.55
1
=0.0176≈0.018
Hence, the mole fraction of urea in the solution is 0.018.