Theory Exercises

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

TypeParticle sizeAppearanceSedimentation
SolutionVery smallTransparentNo
ColloidIntermediateTranslucentUsually no
SuspensionLargeCloudyYes
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.