Mixtures and Raoult's law

You will write functions for the vapour above a mixture of two ideal liquids and for the molar mass of a solute that does not evaporate. Pressures are in kPa.

The idea. $p = x\,p^\circ$, then $P = p_A + p_B$ and $y_A = \dfrac{p_A}{P}$. For a non-volatile solute, $\dfrac{p^\circ - p}{p} = \dfrac{n_B}{n_A}$.

Your tasks.

1. Complete partial_pressure(x, pure) so that it returns Raoult's law for one liquid.
2. Complete total_pressure(x_a, pure_a, pure_b) so that it adds the partial pressures of A and of B.
3. Complete vapour_fraction(x_a, pure_a, pure_b) so that it returns the mole fraction of A in the vapour.
4. Complete molar_mass(p_pure, p_solution, mass_solute, mass_solvent, molar_solvent) so that it returns the molar mass of the solute in g/mol.