Bihar Board - Class 12 Chemistry - Chapter 2: Solution Handwritten Notes

A solution is a homogeneous mixture of two or more substances, where one substance (solute) is dissolved in another substance (solvent). Solutions are an integral part of chemistry and have wide-ranging applications in everyday life and various industries. This chapter explores the types of solutions, the process of dissolution, factors affecting solubility, concentration, and colligative properties, providing a deeper understanding of solutions in different contexts.

Key Points:

Definition of Solution:

A solution is a homogeneous mixture composed of two main components: a solvent (the substance that dissolves) and a solute (the substance that is dissolved). Example: In a sugar solution, sugar is the solute and water is the solvent.

Types of Solutions:

• Solid in Liquid: For example, salt in water.
• Liquid in Liquid: For example, alcohol in water.
• Gas in Liquid: For example, carbon dioxide in water (carbonated drinks).
• Gas in Gas: For example, air, which is a mixture of gases like nitrogen, oxygen, etc.
• Solid in Solid: For example, alloys like brass, which is a mixture of copper and zinc.

Concentration of Solution:

Concentration refers to the amount of solute dissolved in a given amount of solvent. A concentrated solution contains a large amount of solute, while a dilute solution contains a small amount of solute. Concentration is often expressed in terms of molarity (moles of solute per liter of solution), molality (moles of solute per kilogram of solvent), and mass percentage.

Solubility:

Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature and pressure. It is usually expressed in grams of solute per 100 grams of solvent.

Factors Affecting Solubility:

• Temperature: For most solid solutes, solubility increases with temperature. For gases, solubility decreases with increasing temperature.
• Pressure: Solubility of gases in liquids increases with pressure (Henry's Law).
• Nature of Solute and Solvent: Polar solvents dissolve polar solutes, and non-polar solvents dissolve non-polar solutes.

Colligative Properties of Solutions:

• Vapor Pressure Lowering: Addition of solute lowers the vapor pressure of the solvent.
• Boiling Point Elevation: The boiling point of a solution is higher than the boiling point of the solvent.
• Freezing Point Depression: The freezing point of a solution is lower than that of the solvent.
• Osmotic Pressure: The pressure required to stop the osmosis of solvent molecules into the solution.

Raoult’s Law:

Raoult's law states that the partial vapor pressure of each volatile component in a solution is directly proportional to its mole fraction. Mathematically:

P_A = X_A P_A⁰

where P_A is the vapor pressure of component A, X_A is its mole fraction, and P_A⁰ is the vapor pressure of pure A.

Molarity and Molality:

Molarity (M): The number of moles of solute dissolved in one liter of solution. It is given by:

M = Moles of Solute / Volume of Solution in Liters

Molality (m): The number of moles of solute dissolved in one kilogram of solvent. It is given by:

m = Moles of Solute / Mass of Solvent in kg

Conclusion:

In conclusion, solutions are an essential part of chemistry, affecting both everyday life and industrial processes. Understanding the factors that influence solubility and concentration helps us manipulate solutions in practical ways, such as in the pharmaceutical industry, food science, and even in biological systems. The study of colligative properties provides insights into the behavior of solutions, making it essential for applications like antifreeze, salt solutions, and osmotic pressure in biological cells. Solutions are fundamental to numerous chemical reactions and processes, highlighting their importance in various scientific and real-world applications.