Chapter 10 – Solutions (JEE Chemistry)
1. What is a Solution?
A solution is a **homogeneous mixture** of two or more substances.
| Component | Definition |
|---|---|
| Solvent | Component present in larger amount |
| Solute | Component present in smaller amount |
2. Types of Solutions
| Solvent | Solute | Example |
|---|---|---|
| Liquid | Solid | Salt in water |
| Liquid | Liquid | Alcohol in water |
| Gas | Gas | Air |
3. Concentration of Solutions
(a) Mass Percentage
$$\text{Mass \%} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100$$
(b) Mole Fraction
$$X_A = \frac{n_A}{n_A + n_B}$$
(c) Molarity
$$M = \frac{\text{Moles of solute}}{\text{Volume of solution (L)}}$$
(d) Molality
$$m = \frac{\text{Moles of solute}}{\text{Mass of solvent (kg)}}$$
Molality is temperature independent → very important in colligative properties.
4. Solubility
Solubility is the **maximum amount of solute** that can dissolve in a given amount of solvent at a given temperature.
5. Henry’s Law
Henry’s law states that **solubility of a gas** in a liquid is directly proportional to the pressure of the gas.
$$p = k_H x$$
- $p$ = partial pressure of gas
- $x$ = mole fraction of gas
- $k_H$ = Henry’s constant
6. Vapour Pressure of Liquid Solutions
Addition of a non-volatile solute lowers the vapour pressure of the solvent.
7. Raoult’s Law
$$p_A = p_A^0 x_A$$
Valid only for **ideal solutions**.
8. Ideal and Non-Ideal Solutions
| Ideal | Non-Ideal |
|---|---|
| Obeys Raoult’s law | Deviates from Raoult’s law |
| $\Delta H_{mix}=0$ | $\Delta H_{mix} \ne 0$ |
9. Colligative Properties
Properties that depend only on the **number of solute particles**, not their nature.
- Relative lowering of vapour pressure
- Elevation of boiling point
- Depression of freezing point
- Osmotic pressure
10. Relative Lowering of Vapour Pressure
$$\frac{p^0 - p}{p^0} = x_B$$
11. Elevation of Boiling Point
$$\Delta T_b = K_b m$$
- $K_b$ = ebullioscopic constant
12. Depression of Freezing Point
$$\Delta T_f = K_f m$$
- $K_f$ = cryoscopic constant
13. Osmotic Pressure
Osmotic pressure is the pressure required to stop osmosis.
$$\pi = CRT$$
Most accurate method to determine molar mass of polymers.
14. Van’t Hoff Factor
$$i = \frac{\text{Observed colligative property}}{\text{Calculated colligative property}}$$
Accounts for dissociation or association of solute.
15. Abnormal Molecular Mass
Deviation in colligative properties leads to abnormal molar mass.
$$M_{\text{correct}} = \frac{M_{\text{calculated}}}{i}$$
16. Common JEE Traps
- Using molarity instead of molality
- Ignoring Van’t Hoff factor
- Applying Raoult’s law to non-ideal solutions
- Wrong unit conversions
17. Final Revision Checklist
You are exam-ready if you can:
- Convert between concentration terms
- Apply Henry’s law and Raoult’s law correctly
- Solve numerical problems on colligative properties
- Handle abnormal molar mass questions