Is Matter Around Us Pure Class 9 Notes Science - Chapter 2

Chapter: 2

What Are Is Matter Around Us Pure?

Substance

Anything that cannot be broken into further particles by applying any physical processes is called a Substance. Matter can be classified into two types of substances – Pure substances and Mixture

Types of Pure Substances

Elements

  • Cannot be broken down to simpler substances. For example, copper , oxygen , iron , hydrogen , mercury , etc.

Compounds

  • Have fixed composition, can be broken down into elements by chemical or electrochemical reactions. For example, water , methane , sugar , salt , etc.

Mixtures

When different substances are combined with each other a mixture is formed. For Example, Lemonade is a mixture of three substances, Lemon Juice, Sugar and Water.

Types of Mixtures

Homogeneous Mixture: A mixture having a uniform composition throughout is called a homogeneous mixtures or solutions.

• We cannot separate the components of the mixture through physical processes.

Example: Petrol , Vinegar and Soft drinks.

Heterogeneous mixture: A mixture which contain physically distinct parts and have non-uniform composition is called a heterogeneous mixtures.

• We can separate the components through physical processes.

Example: Mixtures of sodium chloride and iron filings, salt and sulphur, oil and water, and paint.

• Particles of matter attract each other.

Solution

A solution is a homogeneous mixture of two or more substances.

Solvent: The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent.

Solute: The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute.

Example: A solution of sugar in water is a solid in liquid solution. In this solution, sugar is the solute and water is the solvent.

Properties of a Solution

• A solution is a homogeneous mixture.

• The particles of a solution are smaller than 1 nm (10–9 metre) in diameter. So, they cannot be seen by naked eyes.

• Due to very small particle size, they do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution.

• The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed, that is, a solution is stable.

Types of Solution

Dilute Solution: A solution in which the concentration of the solute is much less than that of the solvent.

Concentrated Solution: A solution with a large amount of solvent is called a Concentrated Solution.

Saturated Solution: When no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

Unsaturated Solution: If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution.

Solubility: The amount of the solute present in the saturated solution at this temperature is called its solubility.

Concentration of a Solution

The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution, or the amount of solute dissolved in a given mass or volume of solvent.

Concentration of solution = Amount of solute/Amount of solution

Amount of solution = Amount of solute + Amount of solvent

Ways of Expressing the Concentration of a Solution

• Percent by Mass = (Mass of solute / Mass of solution) × 100

• Percent by Volume = (Volume of solute / Volume of solution) × 100

• Molarity (M) = Number of moles of solute / Volume of Solution in litres

• Normality (N) = Number of mole equivalents/ volume of solution in litres

Colloidal Solution

A colloidal solution or a colloid is a heterogenous solution of two or more substances.

Dispersed Phase: The solute-like component or the dispersed particles in a colloid form the dispersed phase.

Dispersion Medium: The component in which the dispersed phase is suspended is known as the dispersing medium.

Properties of a Colloids

• A colloid is a heterogeneous mixture.

• The size of particles of a colloid is very small.

• Colloids are big enough to scatter a beam of light passing through it and make its path visible. This is called Tyndall Effect.

• A colloid is quite stable.

• A special technique of separation known as centrifugation can be used to separate the colloidal particles.

Types of Colloids

On the basis of dispersed phase and dispersion medium

Dispersed phase Dispersing Medium Type Example
Liquid Gas Aerosol Fog, mist, clouds
Solid Gas Aerosol Automobile exhaust, smoke
Gas Liquid Foam Shaving cream
Liquid Liquid Emulsion Milk, Face cream
Solid Liquid Sol Milk of magnesia, mud
Gas Solid Foam Foam, rubber, pumice, sponge
Liquid Solid Gel Cheese, butter, jelly
Solid Solid Solid Sol Coloured gemstone, milky glass

Suspension

A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.

Properties of a Suspension

• Suspension is a heterogeneous mixture.

• The particles of a suspension can be seen by the naked eye.

• The particles of a suspension scatter a beam of light passing through it and make its path visible.

• A suspension is unstable.

Physical And Chemical Changes

Physical Change

These changes occur without a change in composition and no change in the chemical nature of the substance. Example: conversion of ice to water or water vapour.

Chemical Change

These changes occur without a change in composition and no change in the chemical nature of the substance. Example: Burning