Question

How do you calculate the experimental molality of the methanol solution from the freezing point of the solution?

`DeltaT_(f) = K_(f)m`

Answer 1

If you find `K_f` and `T_f` in a table for pure methanol, you can solve the equation for `m` (molality of solution). Moreover, you can calculate the molar mass of an unknown solute to identify it in the lab.

For instance, if the freezing point of pure water is `0°C`, but with the addition of salt it becomes `-2.0°C`, we can derive the molality of salt present.

Water `K_f = (1.86°C)/m`

`2.0°C = (1.86°C)/m * m`
`therefore m approx 1.1m`