Solutions
1.0 Solution
2.0 Methods of expressing concentration of a Solution
3.0 Solubility
4.0 Henry's law
5.0 Raoult's law
6.0 Azotropes
7.0 Colligative Properties
7.1 Relative lowering of vapour pressure
7.2 Elevation in Boiling point
7.3 Depression of Freezing point
7.4 Osmosis and Osmotic pressure
8.0 Abnormal Colligative Properties
7.4 Osmosis and Osmotic pressure
7.2 Elevation in Boiling point
7.3 Depression of Freezing point
7.4 Osmosis and Osmotic pressure
For osmosis you need to know about SPM (Semi-permeable Membrane).
SPM are membranes (membrane means continuous films) through which only solvent molecules can pass.These membrane contains submicroscopic holes which allow the flow of solvent molecules only.
Examples of SPM are Pig bladdder(Natural), Cellophone(Synthetic) and Cellulose(Natural).
$ \to $ If SPM is placed between solvent and solution, the solvent molecules will flow from pure solvent to solution, this process is called osmosis.
This flow continues until equilibrium is reached.
Now, this flow of solvent can be stopped by application of external pressure on solution side. This required external pressure is called Osmotic pressure of Solution.
$ \to $ So,basically in osmosis solvent molecules flow from lower concentration to higher concentration.
Theoretically, we noticed that osmosis depends on concentration of solution at a given temperature, and experimentally following result was found,
$$\begin{equation} \begin{aligned} \pi = CRT \\ \Rightarrow \pi = {n_2}RT/V \\ \Rightarrow \pi = {w_2}RT/V{M_2} \\ \Rightarrow {M_2} = {w_2}RT/\pi V \\\end{aligned} \end{equation} $$
Above equation provides an another method for calculation of molar mass of solute.
This is mostly used method for calculation of molar mass of solute as this method can be used for calculation at room temperature and its magnitude is large even for dilute solution.
$ \to $ Two solutions having same osmotic pressure are called isotonic.
For example: Solution $A$ has osmotic pressure $P$ at temperature ${T_1}$ and other solution $B$ having osmotic pressure $P$ at temperature ${T_2}$ are isotonic even the temperature is different.
$ \to $ A solution having high osmotic pressure in comparison to other solution is called Hypertonic.
$ \to $ A solution having low osmotic pressure in comparison to other solution is called Hypotonic.
Hypertonic and Hypotonic are relative terms. Osmosis is used for preservation of meat and fruit.
Examples of Osmosis in daily life are such as Mango shrivels when put in sline water and blood cell collapse(shrinks) when suspended in saline water.(Both of these phenomena
are due to loss of water).
Question 7. In which side of the container the complex $ [\kern-0.15em[ Cu{(N{H_3})_4} ]\kern-0.15em] $ will be formed?
Solution: $ [\kern-0.15em[ Cu{(N{H_3})_4} ]\kern-0.15em]$ is not going to form as only solvent (water) is allowed to pass through the S.P.M.
Reverse Osmosis
If pressure more then osmotic pressure is applied on solution side then solvent molecules starts moving from solution side to solvent side, this process is called Reverse osmosis.
It means solvent is separated from solution leaving a more concentrated solution behind. Reverse osmosis is used for water purification. SPM used in desalination of water is Cellulose.
Question 8. If ${V_1}$ml of ${C_1}$ solution and ${V_2}$ml of ${C_2}$ solution are mixed then find final concentration and osmotic pressure of solution? Initially osmotic pressure of solution are ${\pi _1}$ and ${\pi _2}$ respectively.
Solution: $$C = \frac{{{C_1}{V_1} + {C_2}{V_2}}}{{{V_1} + {V_2}}}$$$${C_1} = \frac{{{\pi _1}}}{{RT}}$$
and
$${C_2} = \frac{{{\pi _2}}}{{RT}}$$
$$ \Rightarrow \pi = CRT$$
$$ \Rightarrow \pi = \frac{{{\pi _1}{V_1} + {\pi _2}{V_2}}}{{{V_1} + {V_2}}}$$
