Chemistry of Solutions and Colligative Properties

Vocabulary flashcards based on lecture notes covering the chemistry of solutions, concentration units, gas laws, and thermal properties of mixtures.

Solution

A homogeneous mixture of two substances.

Solute

The component of a solution present in the lesser amount.

Solvent

The component of a solution present in the larger amount.

Mass percentage

The ratio of the mass of solute to the mass of solution multiplied by $100$. Formula: $\frac{\text{Mass of Solute}}{\text{Mass of Solution}} \times 100$.

Molarity ($M$)

The number of moles of solute present in one litre of solution, calculated as $M = \frac{n}{V}$ where $V$ is volume in litres.

Henry's Law

A law stating that the solubility of a gas in a liquid is directly proportional to the pressure. It is expressed as $P = K_H \times X$, where $P$ is pressure, $K_H$ is Henry's constant, and $X$ is mole fraction.

Lowering of Vapour Pressure

The difference between the vapour pressure of a pure solvent ($P^o$) and the partial vapour pressure of the solvent in a solution ($P$), expressed as $P^o - P$.

Relative Lowering of Vapour Pressure

The ratio of the lowering of vapour pressure to the vapour pressure of the pure solvent: $\frac{P^o - P}{P^o}$. It is equal to the mole fraction of the solute.

Ideal Solution

A solution that obeys Raoult's Law at all concentrations and temperatures, characterized by $\triangle V_{\text{mix}} = 0$ and $\triangle H_{\text{mix}} = 0$.

Non-Ideal Solution

A solution that does not obey Raoult's Law at all concentrations and temperatures, where interactions between different molecules ($A-B$) are not equal to those between like molecules ($A-A$ or $B-B$).

Positive Deviation from Raoult's Law

Occurs when a solution shows a higher vapour pressure than predicted because the $A-B$ interaction force is weaker than the $A-A$ and $B-B$ forces.

Negative Deviation from Raoult's Law

Occurs when a solution shows a lower vapour pressure than predicted because the $A-B$ interaction force is stronger than the $A-A$ and $B-B$ forces.

Azeotropic mixture

A solution of completely miscible liquids that boils at a constant temperature and distills over without any change in composition; also called a constant boiling mixture.

Minimum boiling Azeotropes

Mixtures formed by liquids showing positive deviation from Raoult's Law, where the boiling point of the azeotrope is lower than that of its individual components.

Maximum boiling Azeotropes

Mixtures formed by liquids showing negative deviation from Raoult's Law, where the boiling point of the azeotrope is higher than that of its individual components.

Colligative properties

Properties of a solution that depend only on the number of solute particles present and not on the chemical nature of the solute.

Elevation of boiling point ($\triangle T_b$)

The increase in boiling point that occurs when a non-volatile solute is dissolved in a volatile solvent; calculated as $\triangle T_b = T_b - T_b^o$, where $\triangle T_b = K_b \times m$.

Ebullioscopic constant ($K_b$)

The elevation in boiling point produced by dissolving $1\text{ mole}$ of substance in $1\text{ kg}$ of solvent; also known as the molal elevation constant.

Freezing point

The temperature at which the liquid and solid forms of a substance exist together in equilibrium, or when the vapour pressure of the liquid equals the vapour pressure of its solid form.

Depression of freezing point ($\triangle T_f$)

The decrease in the freezing point of a solvent upon the addition of a solute; calculated as $\triangle T_f = T_f^o - T_f$, where $\triangle T_f = K_f \times m$.

Cryoscopic constant ($K_f$)

The depression of freezing point produced by dissolving $1\text{ mole}$ of substance in $1\text{ kg}$ of solvent; also known as the molal depression constant.

Osmosis

The spontaneous flow of solvent through a semi-permeable membrane from a pure solvent to a solution.

Osmotic pressure (oldsymbol{\text{\pi}})

The maximum hydrostatic pressure required to prevent the process of osmosis, calculated using oldsymbol{\text{\pi}} = CRT, where $R$ is the gas constant ($0.0821\text{ L}\text{ atm}\text{ K}^{-1}\text{ mol}^{-1}$).

Reverse Osmosis

The process where solvent flows from the solution to the pure solvent through a semi-permeable membrane when pressure higher than semantic pressure is applied to the solution.

van't Hoff factor ($i$)

The ratio of the experimental value of a colligative property to the calculated value ($i = \frac{\triangle_{\text{obs}}}{\triangle_{\text{cal}}}$), or the ratio of normal molar mass to observed molar mass.

Isotonic solutions

Two solutions separated by a semi-permeable membrane that have the same osmotic pressure at a given temperature, resulting in no osmosis.

Hypertonic solution

A solution that has a higher osmotic pressure compared to another solution.

Plasmolysis

The shrinking of cells when placed in a hypertonic solution.

Haemolysis

The rupturing or overflowing of red blood cells.

Mole Fraction ($X$)

The ratio of the moles of one component to the total moles of all components in a solution ($X = \frac{n}{n + N}$).

Solubility

The maximum amount of solute that can be dissolved in $100\text{ ml}$ of solvent.

Anoxia

A condition involving a lack of oxygen that can cause hallucinations, often experienced by climbers at high altitudes.

Raoult's Law

A principle stating that the partial vapour pressure of a volatile component in a solution is equal to the vapour pressure of the pure component multiplied by its mole fraction ($P = P^o \times X$).