Answer:
Boiling T° of solution = 135.6°C
Explanation:
Formula for elevation boiling point is:
ΔT = Kb . m . i
ΔT = Boiling point of solution - Boiling point of pure solvent
Kb = Boiling point elevation constant
m = molality → moles of solute in 1kg of solvent
i = numbers of ions dissolved
FeCl₃ → Fe³⁺ + 3Cl⁻
In the dissociation of the ionic salt, we determined 4 moles of ions dissolved.
3 for chlorides and 1 for iron. Then i = 4
m → We convert the mass of solute to moles:
90 g . 1mol / 162.2g = 0.555 moles
650 g of solvent = 0.650 kg of solvent
m = 0.555 mol/0.650kg → 0.85
We replace data at formula
Boiling T° of solution - 129.90°C = 1.67°C . kg/mol . 0.85 mol/kg . 4
Boiling T° of solution = 1.67°C . kg/mol . 0.85 mol/kg . 4 + 129.90°C
Boiling T° of solution = 135.6°C
