Home » CBSE Class 9 Chemistry Notes for Chapter 2  Is Matter Around us Pure?

CBSE Class 9 Chemistry Notes for Chapter 2  Is Matter Around us Pure?

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CHAPTER 2 IS MATTER AROUND US PURE?

 

MIXTURE

A mixture is a combination of more than one pure substance.

 

Types of mixtures:

Homogeneous mixture: When a mixture has a uniform composition throughout, it is known as a homogeneous mixture.

Heterogeneous mixture: When a mixture has a non-uniform composition, it is known as a heterogeneous mixture.

 

SOLUTION

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

A solvent is the liquid which is used to dissolve a substance. A solute is the substance that is dissolved in the solvent.

A solute and a solvent together form a solution.

Properties of a solution:

  • A solution is a homogeneous mixture.
  • The particles of a solution are smaller than 1 nm in diameter.
  • The particles of a solution do not scatter a beam of light passing through a solution.
  • The solute particles cannot be separated from the mixture by simple filtration.

 

Concentration of a solution

At any temperature, a solution is said to be saturated if there is as much solutes dissolved in it as it is capable of dissolving. If the amount of solute contained in the solution is less than the saturation level, the solution is said to be unsaturated.

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

                           Concentration of solution= (Amount of solute)/(Amount of solution)

 

                     Mass by mass % of a solution= (Mass of solute)/(Mass of solution) X 100

 

                Mass by volume % of a solution=(Mass of solute)/(Volume of solution)

 

SUSPENSION

A heterogeneous mixture in which the solute particles do not dissolve but remain suspended in the solution. These particles are visible to the naked eye.

The particles also scatter a beam of light passing through it. The solute can be separated from the solvent by filtration.

 

COLLOIDAL SOLUTION

The particles of a colloid are uniformly spread throughout the solution. It is a heterogeneous solution. The particles are smaller than the particles in a suspension and do not settle down when the solution is left undisturbed. These particles cannot be seen with naked eyes and they also scatter the beam of light passing through the solution. This scattering is called Tyndall Effect.

The solute particles are called dispersed phase and the solvent is called the dispersion medium.

 

PURE SUBSTANCES

Pure substances can either be elements or compounds.

 

 

ELEMENTS

An element is s substance that cannot be broken down into simpler substances. E.g. Oxygen, Iron. There are three types of elements: Metals, non-metals and metalloids.

Metals

  • Metals have lustre.
  • Metals usually are silver grey or golden yellow in colour.
  • Metals conduct heat and electricity.
  • Metals are ductile, malleable, and sonorous.
  • g. Iron, silver, sodium, etc.

 

Non-metals

  • Non-metals have a variety of colours.
  • Non-metals are poor conductors of heat and electricity.
  • Non-metals are not ductile sonorous and malleable.
  • g. Hydrogen, oxygen, etc.

 

Metalloids

  • These elements have intermediate properties between those of metals and non-metals.
  • g. Boron, silicon, etc.

 

COMPOUNDS

A compound is a substance composed of two or more elements which chemically combine in a fixed proportion.

The constituents of a compound can only be separated by chemical methods.

The properties of a compound are different from the properties of its constituents.

The composition of a compound is same throughout. The same goes from the colour and texture.

E.g. Water, Copper sulphate

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