Is Matter Around Us Pure?

What is a Mixture?

Meaning of “Pure”

• Everyday Meaning:
  • In daily life, pure means free from adulteration, for example pure milk or pure ghee.

• Scientific Meaning:
  • Scientifically, a pure substance contains only one kind of particle.
  • Example: distilled water, pure copper.

Important Point – A pure substance cannot be separated into simpler substances by physical methods.

Most Matter Around Us

• Most substances found in nature are mixtures, not pure substances.
  • Examples: sea water, soil, air.

What is a Mixture?

• Definition:
  • A mixture is a substance made up of two or more pure substances mixed in any proportion, without any chemical combination.

• Key Features of Mixtures:
  • Composition is variable.
  • Components retain their individual properties.
  • Can usually be separated by physical methods.

Types of Mixtures

Based on uniformity, mixtures are of two types.

a. Homogeneous Mixtures (Solutions)

• Definition:
  • A homogeneous mixture has uniform composition throughout.
• Examples:
  • Salt dissolved in water.
  • Sugar dissolved in water.
  • Copper sulphate solution.

b. Heterogeneous Mixtures

• Definition:
  • A heterogeneous mixture has non-uniform composition.
• Examples:
  • Oil and water.
  • Iron filings and sulphur.
  • Sand in water.

Alloys

• Definition:
  • Alloys are mixtures of two or more metals or a metal and a non-metal.
• Examples:
  • Brass = Copper (≈70%) + Zinc (≈30%).
• Why Alloys are Mixtures:
  • They have variable composition.
  • They retain properties of constituent elements.
  • They are not compounds.

What is a Solution?

Definition

• A solution is a homogeneous mixture of two or more substances, showing homogeneity at particle level.

Components of a Solution

• Solvent: The component present in larger amount that dissolves the other substance.
• Solute: The component present in smaller amount that gets dissolved.

Examples

1. Sugar solution → Sugar (solute) + Water (solvent).
2. Tincture of iodine → Iodine (solute) + Alcohol (solvent).
3. Soda water → Carbon dioxide (solute) + Water (solvent).
4. Air → Nitrogen (78%) + Oxygen (21%) + other gases.

Properties of a Solution

• Homogeneous mixture.
• Particle size less than 1 nm.
• Particles cannot be seen with naked eye.
• Does not scatter light (no Tyndall effect).
• Stable mixture; particles do not settle on standing.
• Components cannot be separated by filtration.

Concentration of a Solution

Meaning

Concentration is the amount of solute present in a given amount of solution or solvent.

Types Based on Amount of Solute

1. Dilute Solution:
   • Contains small amount of solute.
2. Concentrated Solution:
   • Contains large amount of solute.
3. Saturated Solution:
   • At a given temperature, no more solute can dissolve in the solution.
4. Unsaturated Solution:
   • Contains less solute than its saturation limit.

Important NCERT Point

Different substances have different solubilities in the same solvent at the same temperature.

Effect of Temperature on Solubility

• Heating increases solubility of most solids.
• Cooling a saturated solution causes excess solute to crystallize out.

Ways to Express Concentration

1. Mass by Mass Percentage:
   • Mass of solute / Mass of solution × 100
2. Mass by Volume Percentage:
   • Mass of solute / Volume of solution × 100
3. Volume by Volume Percentage:
   • Volume of solute / Volume of solution × 100

Example Calculation

• Given: 40 g salt + 320 g water
• Total mass = 360 g
• Mass % = (40 / 360) × 100 = 11.1%

What is a Suspension?

Definition

• A suspension is a heterogeneous mixture in which solid particles are dispersed in a liquid and do not dissolve.

Properties of a Suspension

• Heterogeneous mixture.
• Particles are visible to naked eye.
• Particles scatter light (Tyndall effect).
• Particles settle down on standing (unstable).
• Components can be separated by filtration.

Key Comparison

Solutions → Stable, homogeneous, no light scattering.
Suspensions → Unstable, heterogeneous, show settling and filtration.

What is a Colloidal Solution?

Definition

• A colloid or colloidal solution is a mixture in which particles are uniformly distributed but not dissolved.
• It appears homogeneous to the naked eye but is actually heterogeneous.
• Example: milk.

Properties of a Colloid

• Particle size is too small to be seen by naked eyes.
• Particles do not settle down on standing, hence colloids are stable.
• Colloidal particles scatter light, showing the Tyndall effect.
• Cannot be separated by ordinary filtration.
• Can be separated by centrifugation.
• Colloidal particles show zig-zag motion called Brownian movement.

Components of a Colloid

1. Dispersed Phase:
   • The solute-like component present in small quantity.
2. Dispersion Medium:
   • The medium in which the dispersed phase is suspended.

Examples of Colloids

• Mist, fog, smoke, milk, jelly, butter, foam, clouds.

Dispersed Phase	Dispersing Medium	Type	Example
Liquid	Gas	Aerosol	Fog, clouds, mist
Solid	Gas	Aerosol	Smoke, automobile exhaust
Gas	Liquid	Foam	Shaving cream
Liquid	Liquid	Emulsion	Milk, face cream
Solid	Liquid	Sol	Milk of magnesia, mud
Gas	Solid	Foam	Foam, rubber, sponge, pumice
Liquid	Solid	Gel	Jelly, cheese, butter
Solid	Solid	Solid Sol	Coloured gemstone, milky glass

Special Names of Sols (Based on Dispersion Medium)

• Water → Hydrosol or Aquasol
• Alcohol → Alcosol
• Benzene → Benzosol
• Gas → Aerosol

Important Colloid Phenomena

• Tyndall Effect
  • Scattering of light by colloidal particles, making the path of light visible.
• Brownian Movement
  • Random zig-zag motion of colloidal particles due to collision with dispersion medium particles.
• Electrophoresis
  • Movement of charged colloidal particles under an electric field.
• Coagulation
  • Process of separating colloidal particles by adding electrolytes such as NaCl, BaCl₂, or alum.
• Emulsions
  • Colloids where both dispersed phase and dispersion medium are liquids.

Types of Emulsions

• Oil-in-water emulsion
• Water-in-oil emulsion

Emulsifying agents are used to stabilize emulsions.
Breaking of emulsions is called demulsification.

Physical and Chemical Changes

Physical Changes

• Changes in physical properties like colour, shape, density, melting point, or boiling point.
• No new substance is formed.
• Chemical composition remains unchanged.

Examples:

• Ice melting into water
• Water boiling into steam

Chemical Changes

• Changes in chemical composition leading to formation of new substances.
• Involve chemical reactions.

Examples:

• Burning of oil
• Rusting of iron

Burning of a Candle
Physical change → Melting of wax
Chemical change → Burning of wax to form carbon dioxide and water

Types of Pure Substances

Pure substances are classified into elements and compounds.

a. Elements

Definition

• An element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.

Classification of Elements

1. Metals
   • Properties:
   • Lustrous (Shiny)
   • Malleable (can be hammered into thin sheets)
   • Ductile (can be drawn into wires)
   • Sonorous (make a ringing sound when hit)
   • Good conductors of heat and electricity
   • Examples: Gold, silver, copper, iron, sodium, potassium
   • Note: Mercury is the only metal that is liquid at room temperature.
2. Non-Metals
   • Properties:
     • Dull in appearance
     • Poor conductors of heat and electricity
     • Not shiny, sonorous, malleable or ductile
   • Examples: Hydrogen, oxygen, iodine, carbon, bromine, chlorine
3. Metalloids
   • Properties intermediate between metals and non-metals
   • Examples: Boron, silicon, germanium

Important Facts about Elements

• Over 100 elements are known.
• 92 occur naturally.
• Most elements are solids at room temperature.
• 11 elements are gases at room temperature.
• Mercury and bromine are liquids at room temperature.
• Gallium and cesium melt slightly above room temperature.

b. Compounds

Definition

• A compound is a substance formed when two or more elements combine chemically in a fixed proportion.

Differences Between Mixtures and Compounds

Mixtures

• Components mix physically
• Variable composition
• Retain properties of constituents
• Components separable by physical methods

Compounds

• Components combine chemically
• Fixed composition
• New substance has different properties from its constituents.
• Components can be separated only by chemical or electrochemical reactions.

Chapter Summary

Mixture

• A mixture contains more than one substance, which may be elements, compounds, or both, mixed in any proportion.
• The components of a mixture do not combine chemically and retain their individual properties.
• Mixtures can be separated into pure substances by using suitable physical separation techniques.

Solution

• A solution is a homogeneous mixture of two or more substances.
• The component present in larger amount is called the solvent.
• The component present in smaller amount is called the solute.
• Solutions have uniform composition throughout.

Concentration of a Solution

• The concentration of a solution refers to the amount of solute present in a given amount of solvent or solution.
• It can be expressed per unit mass or per unit volume of the solution.
• Solutions may be dilute, concentrated, unsaturated, or saturated depending on solute content.

Suspension

• A suspension is a heterogeneous mixture in which insoluble particles are dispersed in a liquid.
• The particles of a suspension are large enough to be seen with the naked eye.
• Suspension particles settle down on standing and can be separated by filtration.

Colloids

• Colloids are heterogeneous mixtures with particle sizes intermediate between solutions and suspensions.
• The particles are too small to be seen with the naked eye but large enough to scatter light (Tyndall effect).
• Colloids appear homogeneous but are actually heterogeneous in nature.
• The particles are called the dispersed phase, and the medium in which they are distributed is called the dispersion medium.
• Colloids are widely used in daily life and various industries.

Pure Substances

• Pure substances have a fixed composition and definite properties.
• They can be classified into elements and compounds.

Elements

• An element is a form of matter that cannot be broken down into simpler substances by chemical reactions.
• Elements consist of only one type of atom.

Compounds

• A compound is a pure substance formed when two or more different elements combine chemically in a fixed proportion.
• The properties of a compound are entirely different from the properties of its constituent elements.

Mixtures vs Compounds

• Mixtures show the properties of their constituent elements or compounds.
• Compounds have properties different from the elements that form them.