Definitions [12]
Define the term solution.
A homogeneous mixture of two or more substances, whose relative amounts may be changed within certain limits, is called a solution.
Define:
Solute
A solute is a substance that dissolves in a medium, which can be water or any other substance. A solute is in a smaller quantity in a solution. e.g., sodium chloride.
Define the term solute.
The substance which dissolves or disappears in the solvent, i.e., liquid, to form a solution is called a solute. E.g., sodium chloride.
Define Solvent.
A solvent is a medium in which a solute dissolves. It is in large quantity in a solution. Water is the most common solvent. The other solvents are alcohol, carbon tetrachloride, etc.
Example: Water
Define the term solution with reference to the addition of sodium chloride to water.
A homogenous mixture of a solute in a solvent is called a solution.
Define isotonic solutions.
Two or more solutions exerting the same osmotic pressure are called isotonic solutions.
When two solutions are separated by a semipermeable membrane and no osmosis occurs, i.e., there is no net flow of water on either side through the membrane, the solutions are said to be isotonic solutions. If the membrane is perfectly semipermeable, the two solutions possess the same osmotic pressure and are also referred to as iso-osmotic solutions.
Define the term:
Ideal solution
It is characterised as a solution that adheres to Raoult's Law, with no interactions between the molecules and no volume or heat change during mixing.
For an ideal solution, Enthalpy of mixing of the pure components to form the solution is Δmix H = 0 and the volume of mixing is Δmix V = 0.
A solution in which no solute can be dissolved further at a given temperature is called a saturated solution.
A solution which contains more solute than would be necessary to saturate it at a given temperature is called a supersaturated solution.
A solution in which more solute can be dissolved without raising the temperature is called an unsaturated solution.
It is defined as the amount of solute that can be dissolved in 100 g of the solvent at the given conditions. It is also expressed as the maximum quantity of solute moles that can be dissolved in solvent to form 1 dm³ of solution.
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Unsaturated solution: If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution. (till it is dissolving).
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Saturated solution: When no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.
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Solubility: The amount of the solute present in the saturated solution at this temperature is called its solubility.
Theorems and Laws [1]
Statement: The solubility of a gas in a liquid is directly proportional to the pressure of the gas over the solution.
S = KH⋅P
Where S = solubility (mol L⁻¹), P = pressure (bar), KH = Henry's law constant (mol L⁻¹ bar⁻¹).
Gases like NH₃ and CO₂ do NOT obey Henry's law (they react with water).
Key Points
Based on the physical states of solute and solvent, there are 9 types of solutions:
| S.No. | Solute | Solvent | Example |
|---|---|---|---|
| 1 | Solid | Liquid | Sea water, sugar in water, benzoic acid in benzene |
| 2 | Solid | Solid | Alloys — brass, bronze |
| 3 | Solid | Gas | Iodine in air |
| 4 | Liquid | Liquid | Ethanol in water, gasoline |
| 5 | Liquid | Solid | Amalgam (mercury in silver) |
| 6 | Liquid | Gas | Chloroform in nitrogen |
| 7 | Gas | Liquid | Carbonated water (CO₂ in water), O₂ in water |
| 8 | Gas | Solid | H₂ in palladium |
| 9 | Gas | Gas | Air (O₂, N₂, Ar mixture) |
Factors Affecting Solubility
| Factor | Effect |
|---|---|
| Nature of solute & solvent | "Like dissolves like" — similar chemical character dissolves easily |
| Temperature (solid in liquid) | Endothermic: solubility increases with T; Exothermic: solubility decreases with T |
| Temperature (gas in liquid) | Solubility decreases with increase in temperature |
| Pressure (solid/liquid in liquid) | No effect (incompressible) |
| Pressure (gas in liquid) | Solubility increases with increasing pressure |
