Answer:
Boiling point of the solution is 82.3°C
Explanation:
Boiling point elevation is defined as the increasing of a boiling point of a substance by the addition of a solute. The formula is:
ΔT = K×m×i
Where ΔT is change in temperature (Final T - 80.1°C), K is boiling point elevation constant (2.53°C/m), m is molality of the solution (moles of naphthalene / kg of benzene) and i is Van't Hoff factor (1 for Naphthalene)
Moles of 70.6g of naphthalene are:
70.6g × (1mol / 128.16g) = 0.5509 moles
Kg of 722mL of benzene are:
722mL × (0.877g / mL) × (1kg / 1000g) = 0.633kg of benzene
Replacing in boiling point elevation formula:
(T - 80.1°C) = 2.53°C/m×(0.5509mol / 0.633kg)×1
T - 80.1°C = 2.2°C
T = 80.1°C + 2.2°C
T = 82.3°C
The boiling point of the solution is 82.21°C.
Number of moles of solute = 70.6 g/128.16 g/mol = 0.55 moles
Mass of solvent= density of solvent× volume of solvent
= 722 mL × 0.877 g/mL = 633.2 g or 0.6332 Kg
Molality of the solution = 0.55 moles/0.6332 Kg = 0.869 m
We know that;
ΔT = K m i
ΔT = Boiling point depression
K = Boiling point constant
m = molality of solution
i = Van't Hoff factor
ΔT = 2.53°C/m × 0.869 m × 1
ΔT = 2.2°C
Recall that;
ΔT = Boiling point of solution- Boiling point of pure solvent
Boiling point of solution = Boiling point of pure solvent + ΔT
Boiling point of solution = 80.1°C + 2.2°C
Boiling point of solution = 82.21°C
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