To calculate molar mass by freezing point depression, determine the change in freezing point temperature using the freezing point depression constant, and then evaluate molatility. Once molatility is obtained, use it to calculate moles. Molar mass can be calculated by substituting the obtained value into the molar mass equation.
- Determine change in freezing point temperature
Using suitable techniques, calculate the difference between the freezing point of the solution and the freezing point of the solvent.
- Calculate molatility using the freezing point depression constant
Use the equation (change in temperature = molatility x freezing point depression constant) by putting in the value obtained from step 1 and solving for molatility. The value of the freezing point depression constant varies for every solvent. Choose the right one for your solvent as per international standards by referring to an appropriate chart of freezing points for solvents.
- Calculate moles from the molatility equation and substitute into molar mass equation
Use the equation (molatility = moles / kilograms of solvent) to calculate moles. After that, use (molar mass = grams/moles) to calculate the molar mass of the solution. To convert kilograms to grams, multiply the number by 1000 so that the units are homogeneous throughout the calculation.