0.5g of salt dissolved in 25g of water . calculate the% amount of the salt in the solution
0.5g of salt dissolved in 25g of water . calculate the% amount of the salt in the solution
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Explanation:
Wt. of KCl(w)=0.5g
Wt. of water (W)=100g
Molecular wt (m) of KCl=39+35.5=74.5
Apply the relation of freezing point depression (ΔT f ) with molecular weight of the solute:
ΔT
f
caca =
W×m
K
f
×1000×w
=
100×74.5
1.86×1000×0.5
=0.124
o
C
ΔT
f
obs
=0
o
C+0.24
o
C=0.24
o
C
VAn't Hoff factor (i)=
ΔT
f
cal
ΔT
f
obs
=
0.124
0.24
=1.93
The degree of dissociation (α) of KCl is:
α=
n−1
i−1
where n= number of ions
Here n=2 for K
+
and Cl
−
=
2−1
1.93−1
=
1
0.93
∴α=0.93 or 93%
Thus, the degree of dissociation of the salt is 93% or 0.93.