Answer – We are given, Cyclohexane freezing
point = 6.50∘C , Kf = 20.0oC/m
Mass of biphenyl = 0.771 g , mass of cyclohexane = 25.0 g
First we need to calculate the moles of biphenyl
Moles of biphenyl = 0.771 g / 154.211 g.mol-1
                            Â
= 0.005 moles
So molality of biphenyl = 0.005 moles / 0.025 kg = 0.200 m
We know the formula for freezing point depression
ΔTf = Kf*m
      = 20.0oC/m *
0.200 m
      = 4.00oC
We know the
Freezing point = Freezing point of pure solvent
– ΔTf
                      Â
= 6.50oC – 4.00oC
              Â
        =
2.4oC
