Day: May 21, 2022

class 9 chapter notes (part 2)


Impure substances are commonly called mixtures. A mixture is a material containing two or more elements or compounds that are in close contact and are mixed in any proportion.

  1. A mixture may be homogeneous or heterogeneous.
  2. The composition of a mixture is variable.
  3. A mixture does not have a definite melting point or a boiling point.
  4. Energy is neither absorbed nor evolved during the formation of a mixture.
  5. The properties of a mixture are the properties of its constituents.

Mixtures can be homogeneous or heterogeneous. A homogeneous mixture has a uniform composition throughout its mass. For example, sugar or salt dissolved in water, alcohol in water, etc. While in a heterogeneous mixture the composition is not uniform throughout its mass. Different portions of a heterogeneous mixture show different properties. There are visible sharp boundaries. Example: Oil and water, salt and sand, etc.

Types of mixtures

Heterogeneous mixture

A heterogeneous mixture is the mixture that consists of physically distinct parts, each with different properties. Examples of heterogeneous mixture are mixture of potassium dichromate an iron filling and salt and sugar that have been stirred together.

A heterogeneous mixture of salt and sugar is said to be composed of two different phases: one of the phases is salt, the other is sugar. In heterogeneous mixture, the composition is not uniformed throughout and sometimes the different component can be observed. For example, the mixture of salt in sugar, grains and pulses along with some dirt (often stone) pieces, are heterogeneous mixture.

Homogeneous mixture

 A homogeneous mixture is a mixture that is uniform in its properties throughout given samples. When sodium chloride is dissolved in water. Air is a gaseous solution, principally of two elementary substances, nitrogen and oxygen, which are physically mixed but not chemically combined.

In a homogeneous mixture, the component completely mixed with each other and its composition is uniformed throughout. Sugar solution and air are thus, the examples of homogeneous mixtures. 

Characteristics of mixture

  • Constituents of a mixture can be present in any ratio.
  • Mixture may be heterogeneous or homogeneous.
  • Constituents of a mixture can be separated by easy mechanical means.

Examples of Mixtures

  • Coke is a mixture of water, sugar, flavourings, and carbon dioxide gas.
  • Milk is a mixture of water with various proteins, fats, and other substances.
  • Stainless steel is a mixture (alloy) of iron, carbon, chromium, and nickel. Carbon gives hardness to the mixture. Chromium and nickel give a silvery look to the mixture.