Chapter 1: Solutions
Key Topics: Types of solutions, Methods of expressing concentration, Henry's Law, and Gas Solubility.
1. Definition & Basic Concepts
A solution is defined as a homogeneous mixture of two or more chemically non-reacting substances.
- Solute: The component present in a smaller proportion in the solution.
- Solvent: The component present in a larger proportion which determines the physical state of the solution.
2. Types of Solutions
| Type of Solution | Solute | Solvent | Common Examples |
|---|---|---|---|
| Solid in Solid | Solid | Solid | Copper dissolved in gold, Alloys (Brass) |
| Solid in Liquid | Solid | Liquid | Glucose or salt dissolved in water |
| Solid in Gas | Solid | Gas | Camphor in nitrogen gas, Smoke |
| Liquid in Solid | Liquid | Solid | Amalgam of mercury with sodium |
| Liquid in Liquid | Liquid | Liquid | Ethanol dissolved in water |
| Liquid in Gas | Liquid | Gas | Chloroform mixed with nitrogen gas |
| Gas in Solid | Gas | Solid | Solution of hydrogen in palladium |
| Gas in Liquid | Gas | Liquid | Oxygen or $\text{CO}_2$ dissolved in water |
| Gas in Gas | Gas | Gas | Air (Mixture of $\text{O}_2$ and $\text{N}_2$) |
3. Concentration Expressions & Formulae
i. Mass Percentage $(w/W)$:
$$\text{Mass\% of solute} = \frac{\text{Mass of solute}}{\text{Total mass of solution}} \times 100$$
ii. Volume Percentage $(v/V)$:
$$\text{Volume\% of solute} = \frac{\text{Volume of solute}}{\text{Total volume of solution}} \times 100$$
iii. Mass by Volume Percentage $(w/v)$:
$$\text{Mass by Volume\%} = \frac{\text{Mass of solute in grams}}{\text{Volume of solution in mL}} \times 100$$
iv. Parts Per Million (ppm):
$$\text{ppm (Component A)} = \frac{\text{Number of parts of component A}}{\text{Total number of parts of all components}} \times 10^6$$
v. Mole Fraction ($\chi$):
For a binary mixture of components $A$ and $B$:
$$\chi_A = \frac{n_A}{n_A + n_B}$$
$$\chi_B = \frac{n_B}{n_A + n_B}$$
$$\chi_A + \chi_B = 1$$
vi. Molarity ($M$):
Moles of solute per liter of solution:
$$M = \frac{\text{Moles of solute}}{\text{Volume of solution in Liters}}$$
$$M = \frac{W_B \times 1000}{M_B \times V \text{ (in mL)}}$$
vii. Molality ($m$):
Moles of solute per kilogram of solvent:
$$m = \frac{\text{Moles of solute}}{\text{Mass of solvent in Kilograms}}$$
$$m = \frac{W_B \times 1000}{M_B \times W_A \text{ (in grams)}}$$
viii. Normality ($N$):
Gram equivalents of solute per liter of solution:
$$N = \frac{\text{Number of gram equivalents of solute}}{\text{Volume of solution in Liters}}$$
$$N = \frac{W_B \times 1000}{E_B \times V \text{ (in mL)}}$$
4. Henry's Law & Dissolution
Henry's Law states that at a constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas present above the surface of the liquid.
Henry's Law Equation:
$$p = K_H \cdot x$$
Where:
$$p = \text{Partial pressure of the gas}$$
$$x = \text{Mole fraction of the gas in solution}$$
$$K_H = \text{Henry's Law constant}$$
5. Key Chemical Reactions & Equations
Dissolution of Carbon Dioxide Gas in Water (Aerated Drinks):
$$\text{CO}_2\text{(g)} + \text{H}_2\text{O(l)} \rightleftharpoons \text{H}_2\text{CO}_3\text{(aq)}$$
Dissolution of Solid Salts (e.g., Sodium Chloride):
$$\text{NaCl(s)} \xrightarrow{\text{H}_2\text{O}} \text{Na}^+\text{(aq)} + \text{Cl}^-\text{(aq)}$$