A solution consists of a solute dissolved in a solvent.
Common examples include sugar in milk (solute: sugar, solvent: milk) and salt in water (solute: salt, solvent: water).
Generally, the solvent is in a greater quantity than the solute.
Solvent and Solute
Solvent: The substance in which the solute is dissolved, usually present in a larger amount (e.g., water in saltwater).
Solute: The substance that is dissolved in the solvent (e.g., salt in saltwater).
The solubility of a solute in a given solvent depends on the nature of both the solute and solvent.
Representing Solutions
Solutions can be represented in various ways such as molarity, mass/volume percentage, etc.
Molarity (M): Number of moles of solute per liter of solution.
Formula: M = moles of solute / liters of solution
Mass Percentage: (mass of solute / mass of solution) × 100
Volume Percentage: (volume of solute / volume of solution) × 100
Properties of Solutions
Saturated Solutions
A solution is saturated when no more solute can be dissolved in the solvent at a given temperature.
Saturation point depends on temperature and nature of solute and solvent.
Vapour Pressure
Vapour pressure is the pressure exerted by the vapours of a liquid in equilibrium with its liquid phase.
It depends on temperature and the nature of the liquid.
Raoult's Law: Vapour pressure of a solution is directly proportional to the mole fraction of the solvent.
Colligative Properties
Properties that depend on the number of solute particles but not their nature.
Important colligative properties include:
Relative lowering of vapour pressure
Elevation of boiling point
Depression of freezing point
Osmotic pressure
Elevation of Boiling Point
When a non-volatile solute is added to a solvent, the boiling point of the solution is higher than that of the pure solvent.
Formula: ΔTb = Kb × m (where Kb is the ebullioscopic constant, and m is the molality of the solution).
Depression of Freezing Point
Addition of a non-volatile solute lowers the freezing point of the solvent.
Formula: ΔTf = Kf × m (where Kf is the cryoscopic constant).
Osmotic Pressure
The pressure required to stop the flow of solvent into the solution through a semipermeable membrane.
Formula: π = iCRT (where π is the osmotic pressure, i is the van't Hoff factor, C is the molarity, R is the gas constant, and T is the temperature in Kelvin).
Isotonic Solutions
Solutions having the same osmotic pressure are termed as isotonic.
Such solutions do not experience net flow of solvent between them.
Reverse Osmosis (RO)
A process used for purifying water by applying pressure greater than the osmotic pressure to reverse the flow of solvent through a semi-permeable membrane.
Commonly used in water purification systems to remove salts and impurities.
Practice Problems
Ensure thorough understanding by working through practice problems related to molarity, mass/volume percentage, boiling point elevation, freezing point depression, and osmotic pressure calculations.