Mixtures are combinations of substances where each component keeps its own properties.
1. Pure Substances and Mixtures
- Pure substance: one component with fixed composition.
- Mixture: two or more substances physically combined.
Mixtures can be:
- Homogeneous (one phase, uniform composition), also called solutions.
- Heterogeneous (more than one visible phase).
2. Solutions
In a solution:
- Solute: substance that dissolves.
- Solvent: substance that dissolves the solute.
Example: salt water
- Solute: $\mathrm{NaCl}$
- Solvent: $\mathrm{H_2O}$
3. Concentration Units
Concentration in g/L
$$
c = \frac{m_{\text{solute}}}{V_{\text{solution}}}
$$
Mass percentage
$$
\%\,m/m = \frac{m_{\text{solute}}}{m_{\text{solution}}} \times 100
$$
Volume percentage
$$
\%\,v/v = \frac{V_{\text{solute}}}{V_{\text{solution}}} \times 100
$$
Concentration in g/mL
$$
c = \frac{m_{\text{solute}}}{V_{\text{solution}}}
$$
4. Solubility
Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a fixed temperature.
Types of solutions:
- Unsaturated: can dissolve more solute.
- Saturated: contains maximum dissolved solute.
- Supersaturated: contains more than equilibrium amount (unstable).
Factors that affect solubility:
- Temperature
- Nature of solute and solvent
- Pressure (important for gases)
5. Dilution
Dilution lowers concentration by adding solvent.
If solute amount stays constant:
$$
C_1V_1 = C_2V_2
$$
6. Colloids and Suspensions
| Type | Particle size | Appearance | Sedimentation |
|---|---|---|---|
| Solution | Very small | Transparent | No |
| Colloid | Intermediate | Translucent | Usually no |
| Suspension | Large | Cloudy | Yes |
Colloids show the Tyndall effect (light scattering).
7. Separation Methods
Choose method according to particle size and physical properties.
- Filtration: insoluble solid + liquid
- Decantation: liquids with different densities or solid-liquid after settling
- Evaporation/Crystallization: recover dissolved solid
- Distillation: separate liquids by different boiling points
- Magnetic separation: magnetic solids from nonmagnetic materials
- Chromatography: separate dissolved substances by different affinities
8. Example Workflow
For a mixture with iron, salt, sand, and floating plastic:
1. Magnetic separation for iron. 2. Add water and filter to remove sand/plastic from salt solution. 3. Evaporate water to recover salt. 4. Use density/flotation to separate sand and plastic.