When matter changes from a solid to liquid or from liquid to gas, what kind of change takes place?
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The mathematical expression for the depression in freezing point is given as:
where, = depression in freezing point
= molal depression constant (20.0
)
m = molality
Molality is defined as the ratio of number of moles of solute to the kg of the solvent
Number of moles =
given mass of biphenyl solute = 0.925 g
Molar mass of biphenyl = 154.21 g/mol
Put the values,
number of moles of biphenyl =
=
Molality =
Mass of cyclohexane solvent = 25.0 g
Convert g into kg: 1 kg = 1000 g
Thus, mass of cyclohexane =
= 0.025 kg
Now, put the values in the formula of molality:
Molality =
= 0.236 mole/kg or 0.236 m.
Calculate the depression in freezing point:
=
Now,
=
Hence, freezing point of the solution is .