Is Matter Around Us Pure?

What is a Mixture?

What Does “Pure” Mean?

• Everyday Use: No adulteration (e.g., pure milk).
• Scientific Use: Made of only one kind of particle (e.g., pure water).

Most Matter Around Us

• Most things are mixtures, not pure substances (e.g., sea water, soil).

What is a Mixture?

• Definition: Made of more than one kind of pure substance.
• Examples:
  • Homogeneous Mixtures: Same throughout (e.g., salt in water).
  • Heterogeneous Mixtures: Different parts are visible (e.g., oil in water).

Types of Mixtures

a. Homogeneous Mixtures (Solutions)

• Uniform composition.
• Examples:
  • Salt dissolved in water.
  • Sugar dissolved in water.
• Experiment:
  • Mix water and copper sulphate.
  • Different amounts give different intensities of color.

b. Heterogeneous Mixtures

• Non-uniform composition.
• Examples:
  • Mixtures of iron filings and sulfur.
  • Oil and water.

More to Know: Alloys

• Definition: Mixtures of metals or metals with non-metals.
• Examples:
  • Brass (70% copper, 30% zinc).
• Alloys are mixtures because they retain properties of their constituents and have variable composition.

What is a Solution?

Definition

• A solution is a homogeneous mixture of two or more substances.
• Examples: Lemonade, soda water.

Components of a Solution

• Solvent: The component that dissolves the other (usually larger quantity).
• Solute: The component that is dissolved (usually smaller quantity).

Examples

1. Sugar in Water: Sugar (solute) + Water (solvent).
2. Tincture of Iodine: Iodine (solute) + Alcohol (solvent).
3. Soda Water: Carbon dioxide (solute) + Water (solvent).
4. Air: Oxygen (21%) and Nitrogen (78%).

Properties of a Solution

• Homogeneous mixture.
• Particles are smaller than 1 nm, cannot be seen by naked eyes.
• Does not scatter light; path of light is not visible.
• Solute particles cannot be separated by filtration and do not settle down.

Concentration of a Solution

Definitions

• Dilute Solution: Less solute.
• Concentrated Solution: More solute.
• Saturated Solution: No more solute can dissolve at a given temperature.
• Unsaturated Solution: Less solute than saturation level.

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 in 320 g water.
• Total Mass: 40 g + 320 g = 360 g.
• Mass Percentage: 40/360×100=11.1%

What is a Suspension?

Definition

• A suspension is a heterogeneous mixture where solids are dispersed in liquids.
• The solute particles do not dissolve but remain suspended.

Properties of a Suspension

• Particles are visible to the naked eye.
• The mixture is heterogeneous.
• Particles scatter light (Tyndall effect).
• Particles settle down when left undisturbed.
• Can be separated by filtration.

What is a Colloidal Solution?

Definition

• A colloid or colloidal solution is a mixture where particles are uniformly spread but not dissolved.
• Appears homogeneous but is actually heterogeneous (e.g., milk).

Properties of a Colloid

• Particles are too small to be seen with naked eyes.
• Particles scatter light (Tyndall effect).
• Particles do not settle down when left undisturbed.
• Cannot be separated by filtration but can be separated by centrifugation.

Components of a Colloid

• Dispersed Phase: Solute-like component.
• Dispersion Medium: Component in which the dispersed phase is suspended.

Examples of Colloids

• Mist (water droplets in air).
• Fog, smoke, and milk.

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

Physical and Chemical Changes

Physical Changes

• Changes in physical properties like color, hardness, density, melting point, boiling point.
• Examples: Ice melting into water, water boiling into steam.
• No change in chemical composition.

Chemical Changes

• Changes in chemical properties, forming new substances.
• Examples: Burning of oil, rusting of iron.
• Involves chemical reactions.

Example: Burning a Candle

• Physical Change: Melting of wax.
• Chemical Change: Burning of wax to produce carbon dioxide and wate

Types of Pure Substances

Substances can be classified into two main types based on their chemical composition: elements and compounds.

a. Elements

Definition

• Elements are basic forms of matter that cannot be broken down into simpler substances by chemical reactions.
• Introduced by Robert Boyle and further defined by Antoine Lavoisier.

Types of Elements

1. Metals
   • Properties:
     • Shiny (lustrous)
     • Silvery-grey or golden-yellow color
     • Conduct heat and electricity
     • Can be drawn into wires (ductile)
     • Can be hammered into thin sheets (malleable)
     • Make a ringing sound when hit (sonorous)
   • Examples: Gold, silver, copper, iron, sodium, potassium
   • Note: Mercury is the only metal that is liquid at room temperature.
2. Non-Metals
   • Properties:
     • Show a variety of colors
     • Poor conductors of heat and electricity
     • Not shiny, sonorous, or malleable
   • Examples: Hydrogen, oxygen, iodine, carbon, bromine, chlorine
3. Metalloids
   • Have properties intermediate between metals and non-metals.
   • Examples: Boron, silicon, germanium

Fun Facts

• There are over 100 known elements, with 92 occurring naturally.
• Most elements are solid at room temperature.
• Eleven elements are gases at room temperature.
• Two elements, mercury and bromine, are liquids at room temperature.
• Gallium and cesium become liquid slightly above room temperature.

b. Compounds

Definition

• Compounds are substances composed of two or more elements chemically combined in fixed proportions.

Differences Between Mixtures and Compounds

Mixtures

1. Elements or compounds just mix together without forming a new substance.
2. Variable composition.
3. Shows properties of the constituent substances.
4. Components can be separated by physical methods.

Compounds

1. Elements react to form new substances.
2. Fixed composition.
3. New substance has different properties from its constituents.
4. Components can be separated only by chemical or electrochemical reactions.

Chapter Summary:

• A mixture contains more than one substance (element and/or compound) mixed in any proportion.
• Mixtures can be separated into pure substances using appropriate separation techniques.
• A solution is a homogeneous mixture of two or more substances. The major component of a solution is called the solvent, and the minor component is called the solute.
• The concentration of a solution is the amount of solute present per unit volume or per unit mass of the solution.
• Materials that are insoluble in a solvent and have particles visible to the naked eye form a suspension. A suspension is a heterogeneous mixture.
• Colloids are heterogeneous mixtures with particle sizes too small to be seen with the naked eye but large enough to scatter light. Colloids are useful in industry and daily life. The particles are called the dispersed phase, and the medium in which they are distributed is called the dispersion medium.
• Pure substances can be elements or compounds. An element is a form of matter that cannot be broken down by chemical reactions into simpler substances. A compound is a substance composed of two or more different types of elements chemically combined in a fixed proportion.
• Properties of a compound are different from its constituent elements, whereas a mixture shows the properties of its constituting elements or compounds.