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Freezing point of urea solution is -0.6° C.
How much urea is required to be dissolved in
3 kg water?
[M(urea) = 60 g mol!, K = 1.5°C Kg mol
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1
Answer:
Amount of urea = 1.02g
no. of mole = 1.02/60
Molar mass of urea (NH
2
CONH
2
)=60
Molality =
60
1.02
×
98.5
1000
=0.17259
ΔT
f
=k
f
m⇒0.211=k
f
×0.1759 ...(i)
Let molar mass of unknown compound = M
ΔT
f
=k
f
m
ΔT
f
=k
d
×
M
1.60
.
80.6
1000
0.34=k
f
×
M
19.85
...(ii)
divide equation (i) by (ii)
0.34
0.211
=
19.85
0.1759
×M
M=
0.34×17.59
0.211×19.85
=70gm
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