Short Notes -Class 9- Chemistry – Chapter 2 – Is Matter Around Us Pure

body { overflow: scroll; /* Show scrollbars */

Short Notes -Class 9- Chemistry – Chapter 2 – Is Matter Around Us Pure

Chapter Summary: Is Matter Around Us Pure?

 Physical Nature of Matter:

Particles in gases are well-separated and move freely, while solids have tightly packed particles with minimal movement.

Purity:

Pure Substances:

◆Elements or compounds consisting of only one kind of entity.

◆Cannot be broken down further by chemical or physical means.

◆Have a fixed composition.

◆Example: Diamond, carbon dioxide.

Compounds:

◆Consist of two or more different types of elements in a fixed ratio.

◆Always homogeneous with a constant composition.

◆New substance formed by chemical combination of elements.

◆Example: Water (H2O), Hydrogen Peroxide (H2O2).

Elements:

◆Atoms with the same number of protons in their nuclei.

◆Represented by symbols (e.g., Hydrogen (H), Carbon (C)).

◆Includes metals (e.g., Aluminium, Copper), nonmetals (e.g., Carbon, Boron), and metalloids (e.g., Boron, Silicon).

Mixtures:

◆Substances made up of two or more unrelated chemical components.

◆Can be solutions, suspensions, or colloids.

◆Formed by physically mixing pure substances.

◆Examples: Crude oil, seawater.

Types of Mixtures:

1. Homogeneous Mixture:

◆Uniform composition throughout.

◆Example: Sugar in water.

2. Heterogeneous Mixture:

◆Physically distinct parts with a non-uniform composition.

◆Example: Mixture of salt and iron filings.

Physical vs Chemical Changes:

Physical Changes:

◆Only physical properties change (e.g., shape, size, color, state).

◆No new substance formed.

◆Example: Melting of ice.

Chemical Changes:

◆New substance with different properties formed.

◆Example: Burning of wood.

Solutions:

◆Homogeneous mixture of two or more substances.

◆Particles too tiny to be seen, do not scatter light.

◆Components: solute (dissolved) and solvent (dissolving).

◆Examples of solutes: Sugar, dissolved carbon dioxide.

◆Examples of solvents: Water, ethanol.

Concentration of Solutions:

◆Measured by the amount of solute dissolved in a specific amount of solvent or solution.

◆Types include dilute, concentrated, and saturated solutions.

◆Factors affecting solubility include temperature and pressure.

◆Solubility represented by mass percentage or mass by volume percentage.

Suspensions:

◆Heterogeneous mixture where solute particles remain suspended throughout the medium.

◆Solute particles settle when left undisturbed and can be separated by filtration.

◆Particles are large (>100 mm), visible, and do not pass through filter paper.

Colloids:

◆Mixture where substances are evenly suspended in a fluid.

◆Classified into foams, emulsions, and sols based on dispersed phase and dispersing medium.

◆Exhibit Tyndall effect (scattering of light) when light passes through.

◆Examples include milk of magnesia (sol), shaving cream (foam), and clouds (aerosol).

Evaporation:

◆Process of converting a liquid into vapor.

◆Used to separate volatile components from non-volatile solutes.

◆Examples include clothes drying, cooling hot liquids, and melting ice cubes.

}