Calculating Molar Mass Through Boiling Point Elevation

How can we calculate the molar mass of a compound using boiling point elevation?

Given a solution containing 26.9 g of a molecular compound dissolved in 100.0 g of water with a boiling point of 101.5 °C, how can we determine the molar mass of the compound?

Calculating Molar Mass

To calculate the molar mass of the compound, we need to use the formula for boiling point elevation:

ΔTb = Kb * m

Where:

ΔTb is the boiling point elevation

Kb is the boiling point elevation constant for water

m is the molality of the solution

First, we calculate the molality of the solution:

molality = (moles of solute) / (mass of solvent in kg)

Given that the mass of the solute is 26.9 g and the mass of the solvent (water) is 100.0 g, we can calculate the moles of solute:

moles of solute = mass of solute / molar mass of solute

Next, we convert the mass of the solvent to kg:

mass of solvent = 100.0 g = 0.100 kg

Now we can calculate the molality:

molality = (moles of solute) / (mass of solvent in kg)

Then, we substitute the values into the boiling point elevation formula:

ΔTb = Kb * m

Finally, rearrange the formula to solve for the molar mass:

molar mass = (ΔTb * molality) / Kb

Substitute given values to calculate the molar mass of the compound.