Question

Liquid A having 5 moles and V.P. = 200 mm $Hg$ is mixed with another liquid having B having 10 moles and V.P. = 100 mm $Hg$. Find out the molar ratio of the solute and solvent in the liquid phase. Also find out the P at which liquid starts boiling.

Answer 1

Hint: when more than one compound comes together to form a solution then they do so in specific quantities. The formation of a solution or compound of the substances takes place in specific amounts of volume and pressure. For the analysis and representation of the compounds as such, we need certain measures. The molar ratio is one such measure.

Complete answer:
Solutions are homogeneous mixtures which contain two or more components which mix together. The solution generally contains a solute and a solvent. Generally, the solvent is the component which is present in the higher quantity and the solute is smaller. Generally, the solvent is known as the dispersion medium and the solute is called the dispersed phase.
The relation can be given by the Raoult’s law which states that for a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to the mole fraction present in solution, $p = p^\circ \chi $,
Total moles in the solution = 10 + 5 = 15 moles.
So mole fraction of liquid A = $\dfrac{5}{{15}} = 0.33$
Mole fraction of liquid B = $\dfrac{{10}}{{15}} = 0.66$
Molar ratio of A with B = $\dfrac{{0.33}}{{0.66}} = \dfrac{1}{2}$
So from Raoult’s law, calculating the partial pressures of liquid A = $200 \times 0.33 = 66$
From Raoult’s law, calculating the partial pressures of liquid B = $100 \times 0.66 = 66$
A substance begins to boil when its vapour pressure is equal to the environmental pressure.

So, the total pressure of the liquid = $66 + 66 = 132mmHg$ and the liquid will boil at this pressure.

Note: Solutions can also exist in various states like solid, liquid, or gas.
The solid solutions are called alloys which are the mixture of two or more elements, the liquid state of the mixtures are usually called solutions.
Gases too intermix to form mixtures, since the gases are the state with the most mobile atoms so their mixtures are most usual in nature.