State and explain van't Hoff- Avogardo's law.

Explanation

Statement of van't Hoff-Avogadro's law : At given temperature, equal volumes of the solutions having the same osmotic pressure contain number of solute particles.
Explanation : The equal number of moles of the substances contain equal number of molecles.
The osmotic pressure, `pi`, is given by `pi = CRT`
where C is the concentration of a solution is mol `dm^(-3)`.
`pi = n/V Rt :. pi prop (n)/(V)` at constant temperature .
If two solutions contain, `n_(A)` and `n_(B)` moles of two solutes in the equal volumes (V) of the solutions A and B at the same temperature, then `pi_(A) prop n_(A//V)` and `pi_(B)prop n_(B//V)`
`:. (pi_(B))/(pi_(A)) = (n_(A))/(n_(B))`
If `pi_(A) = pi_(B)`, then `n_A = n_B`.
Thus, two solutions having equal osmotic pressure will contain equal number of moles and hence equal number of the molecules of the substances (solutes).
This is similar to Avogadro's hypothesis for gases. Hence, it is called van't Hoff-Avogadro's law for the solutions.