a)How much would the freezing point change in a 2.5m solution of phenol in benzene? (freezing point of phenol is 7.40 degrees C, freezing point of benzene is 5.12 degrees C)
b)How much would the boiling point change in a 1.0m solution of magnesium chloride in ethanol? (boiling point of ethanol is 1.19 degrees C)
a)
delta T = Kf*m
b)
delta T = i*Kb*m
i is the van't Hoff factor which for MgCl2 is 3 (for three particles).
a) To determine the change in freezing point of a solution, you can use the formula:
ΔTf = Kf * m
Where:
ΔTf = change in freezing point
Kf = cryoscopic constant (molal freezing point depression constant, unique for each solvent)
m = molality of the solution (moles of solute per kilogram of solvent)
In this case, the freezing point depression constant for benzene can be assumed to be 5.12°C/molal. The molality of the solution is given as 2.5 m.
Plug the values into the formula:
ΔTf = 5.12°C/molal * 2.5 m
ΔTf = 12.8°C
Therefore, the freezing point of the solution would decrease by 12.8 degrees Celsius.
b) To determine the change in boiling point of a solution, you can use the formula:
ΔTb = Kb * m
Where:
ΔTb = change in boiling point
Kb = ebullioscopic constant (molal boiling point elevation constant, unique for each solvent)
m = molality of the solution (moles of solute per kilogram of solvent)
In this case, the boiling point elevation constant for ethanol can be assumed to be 1.19°C/molal. The molality of the solution is given as 1.0 m.
Plug the values into the formula:
ΔTb = 1.19°C/molal * 1.0 m
ΔTb = 1.19°C
Therefore, the boiling point of the solution would increase by 1.19 degrees Celsius.