Question

A certain liquid X has a normal boiling point of 128.20°C and a boiling point elevation constant Kb=1.03·°C·kgmol?1. Calculate the boiling point of a solution made of 38.5g of iron(III) chloride (FeCl3) dissolved in 250.g of X.

Be sure your answer is rounded to the correct number of significant digits.

Answer 1

To calculate the new boiling point of the solution, first find the molality by dividing the moles of FeCl3 by the solvent's mass in kg. Then, multiply the molality by the boiling point elevation constant and the van't Hoff factor. Lastly, add the boiling point elevation to the normal boiling point to obtain the new boiling point.

Step-by-step explanation:

The boiling point of a solution can be calculated using the formula ΔT = i × Kb × m, where ΔT is the boiling point elevation, i is the van't Hoff factor (number of particles the solute splits into), Kb is the boiling point elevation constant, and m is the molality of the solution. For iron(III) chloride (FeCl3), the van't Hoff factor is 4 since it dissociates into one Fe3+ ion and three Cl− ions. First, calculate the molar mass of FeCl3 and find the molality by dividing the moles of FeCl3 by the mass of the solvent in kilograms. Then, multiply the molality by the Kb and van't Hoff factor to find the boiling point elevation. Finally, add this value to the normal boiling point of the liquid to find the new boiling point of the solution.

Step 1: Molar mass of FeCl3 = 55.845 (Fe) + 3 × 35.453 (Cl) = 162.204 g/mol

Step 2: Moles of FeCl3 = 38.5g / 162.204 g/mol = 0.237 moles

Step 3: Molality (m) = Moles of solute / Mass of solvent in kg = 0.237 mol / 0.250 kg = 0.948 m

Step 4: Boiling point elevation (ΔT) = i × Kb × m = 4 × 1.03 °C⋅kgmol−1 × 0.948 m = 3.90 °C

Step 5: New boiling point = Normal boiling point + ΔT = 128.20 °C + 3.90 °C = 132.10 °C

Answer 2

129.18 °C

Step-by-step explanation:

The elevation in the boiling point is a colligative property that can be calculated using the following expression.

ΔTb = Kb × b

where,

ΔTb: elevation in the boiling point

Kb: boiling point elevation constant

b: molality

The molality of the solution is:

`b=(38.5gFeCl_(3))/((162.2 g FeCl_(3)/molFeCl_(3)).0.250 kgX) =0.949m`

ΔTb = Kb × b

ΔTb = (1.03 °C.kg/mol) × (0.949 mol/kg) = 0.977°C

The boiling point of the solution is:

128.20°c + 0.977°C = 129.18 °C