Chemistry · Ch 1 — Solutions

Summary

Solution: A homogeneous mixture of two or more substances. Solvent is the component in larger amount; solute in smaller.
Concentration terms:
- Mass percentage = $\frac{\text{mass of solute}}{\text{mass of solution}} \times 100$
- Mole fraction ( $x$ ) = $\frac{\text{moles of component}}{\text{total moles}}$
- Molarity ( $M$ ) = $\frac{\text{moles of solute}}{\text{volume of solution in L}}$
- Molality ( $m$ ) = $\frac{\text{moles of solute}}{\text{mass of solvent in kg}}$
Solubility: Maximum solute that dissolves in a given solvent at a fixed temperature. For gases, follows Henry’s law: $p = K_H \cdot x$ (partial pressure $\propto$ mole fraction in liquid).
Vapour pressure: For a volatile liquid, it is the pressure of its vapour in equilibrium with the liquid. Raoult’s law: For a solution of volatile liquids, $p_A = p_A^\circ x_A$ and $p_B = p_B^\circ x_B$ ; the total vapour pressure is $p_{\text{total}} = p_1^{0}\,x_1 + p_2^{0}\,x_2$ .
Ideal solutions: Obey Raoult’s law at all concentrations; $\Delta H_{\text{mix}} = 0$ , $\Delta V_{\text{mix}} = 0$ .
Non-ideal solutions: Show positive or negative deviations from Raoult’s law; form azeotropes (constant-boiling mixtures).
Colligative properties: Depend only on number of solute particles, not their identity:
- Relative lowering of vapour pressure: $\frac{p^\circ - p}{p^\circ} = x_{\text{solute}}$
- Elevation in boiling point: $\Delta T_b = K_b \cdot m$ …