An aqueous solution of NaCl has boiling point of
102.42 oC. What is the corresponding freezing point of this
solution?
a) -2.42 °C
b) -8.77 °C
c) 8.60 °C
d) 2.42 °C
An aqueous solution of NaCl has boiling point, Tb = 102.42 oC and also we know that the boiling point constant, Kb of water is 0.512 oC/molal.
Using the formula, we can calculate the molality of the given NaCl solution.
, where, Tb*= 100 oC
vant's Hoff factor, i = 2, NaCl completely dissociates into two ions
Now by putting the values,
We can now calculate freezing point of the solution by using the formula of depression in freezing point,i.e.,
, where, Tf*= 0 oC
vant's Hoff factor, i = 2 and Kf = 1.86oC/molal
Therefore option b) -8.77 oC is correct.
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