Physical and Chemical Changes, Solution Notes with PDF

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Types of Changes

Physical Change

• Definition: A change where no new substance is formed and the process is generally reversible.
• Examples:
  • Dissolving sugar in water.
  • Change of water into vapour (evaporation).
  • Melting of ice.
  • Dispersion of white light into seven colours through a prism.
  • The process of sublimation (e.g., solid camphor turning into vapour).
  • A wet soil lump becomes fragile when dried.

Chemical Change

• Definition: A change where one or more new substances with different properties are formed.
• Examples:
  • Souring of milk.
  • Softening of vegetables when cooked (involves chemical breakdown).
  • Blackening of silverware (tarnishing/corrosion).
  • Burning of a candle.
  • Making curd from milk.
  • Decomposition of water.
• Key Characteristic:
  • Chemical reactions proceed faster at higher temperatures because increased molecular motion leads to more frequent and energetic collisions.

Important Processes

Pasteurization

• Definition: A process used to preserve milk by heating it to a specific temperature for a set time and then cooling it suddenly.
• Primary Goal: Sterilisation (killing harmful microbes).
• Clarifications:
  • It is not used for dehydration, fermentation, or distillation.
  • It is not related to the processing of tea.

Corrosion

• Definition: The process of deterioration of a metal due to a chemical reaction with its environment (like oxygen and moisture).
• Examples:
  • Black coating on silver (tarnishing).
  • Green coating on copper (formation of verdigris).
  • Brown coating on iron (rusting).

Osmosis and Reverse Osmosis

• Osmosis:
  • The natural movement of a solvent (like water) from a dilute solution to a more concentrated solution through a semipermeable membrane.
  • Example: Water comes out of a cucumber when salt is added (water moves out of the cucumber cells to the higher salt concentration outside).
• Reverse Osmosis:
  • The reverse of natural osmosis. An external pressure is applied to the concentrated solution, forcing the solvent to pass through the membrane to the dilute side.
  • Application: Used to produce potable water from seawater (desalination).

States and Properties of Matter

Colloids

• Definition: A mixture where one substance is evenly dispersed throughout another in tiny particles.
• Examples and Types:
  • Emulsion (liquid in liquid): Milk.
  • Other Colloids: Blood, Ice cream.
  • Aerosol (liquid in gas): Fog.
• Non-Colloid Example: Honey is a true solution, not a colloid.

Effect of Impurities

• On Boiling Point: Adding impurities to a liquid increases its boiling point.
• On Freezing Point:
  • Adding salt to ice decreases its freezing point (melting point depression), allowing temperatures below 0°C to be achieved.
  • Correction: The statement “salt increases the freezing point of ice” is incorrect.

Properties of Solutions

• When an unsaturated solution is prepared by dissolving a solute (like sugar) in a solvent (like water):
  • The mass of the system remains unchanged (Law of Conservation of Mass).
  • The density, concentration, and volume will change.

Separation Techniques

• Sublimation: Used to separate a mixture where one component sublimes (e.g., separation of sand and naphthalene).
• Chromatography: Used to separate and identify the different substances present in a mixture.
• Crystallisation: A technique used for the purification of solids.

Oxidation Numbers

• Definition: The hypothetical charge of an atom in a compound.
• Examples:
  • Ca in CaO: +2
  • Al in NaAlH₄: +3
  • Mn in MnO₂: +4
  • S in H₂SO₄: +6

Know More About Physical and Chemical Changes, Solution:

• Physical and Chemical Changes, Solution – Old Year Questions
• Physical and Chemical Changes, Solution One Liner Questions & Answers