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Types of Mixtures

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Mixtures are made up of two or more substances. All elements and compounds are pure substances. Most substances around us are mixtures of two or more elements or compounds. Two or more substances mixed ultimately in nay ratio, without involving chemical reaction give rise to a mixture.

Broadly speaking if a chemical reaction takes place, the mixture of constituents is converted into compound. If the chemical reaction does not take place, the mixture of constituents remains a mixture. A mixture is an impure substance made of two or more elements combined physically in any proportions by mass.

Definition

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Mixture are a combination of the properties of the constituent elements or substances. The smallest particle of a mixture is the same as the smallest particle of each constituent. Samples of a given mixture differ in their properties. The constituents of a mixture can be separated by simple physical means. The formation of a mixture is not accompanied by the absorption or the evolution of heat.

A mixture has no definite molecular formula and it has no characteristic melting and boiling point. Based on their composition, mixtures can be of the following types.

Types of Mixtures

Mixtures can also be classified on the basis of nature of the constituents.
  • Solid + solid mixtures
  • Solid + Liquid mixtures
  • Liquid + Liquid mixtures
  • Liquid + Liquid mixtures
  • Liquid + Gas mixtures
  • Gas + Gas mixtures

Homogenoeous Mixture

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Homogeneous mixtures have uniform composition and properties in all parts. These mixtures are those in which the composition and the properties are the same throughout the mixture. Sometimes it is hard to tell whether something is a mixture. The mixture is clear and the salt is not visible. A mixture like this is called a solution. The homogeneous mixtures of liquids and solids are called solutions.

Normally a homogeneous mixture is not obtained if both the components are solid. Perfect mixing becomes improbable in such cases and composition varies from point to point. There is a possibility of obtaining homogeneous mixtures with liquid components. For example, a mixture of water and alcohol on stirring will provide a homogeneous mixture. Salt solution, sugar solution a mixture of ethyl alcohol and water are examples of homogeneous mixtures.

Heterogeneous Mixture

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Heterogeneous mixtures do not have uniform composition and properties throughout. A heterogeneous mixture is one in which the composition is different parts of the mixture. Heterogeneous mixtures are those mixtures in which the composition and properties vary in different parts of the mixture.

Sand mixed in water is an example of a heterogeneous mixture. As the sand settles down the upper layer contains more water and less sand whereas the lower layer contains more sand and less water. A mixture of iron and sulphur is a heterogeneous mixture.

Homogeneous Vs Heterogeneous

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Depending upon the physical state of the compounds of a given mixture, it can be classified into two categories.
  • Homogeneous mixture
  • Heterogeneous mixture

Homogeneous mixture Heterogeneous mixture
A homogeneous mixture (also known as solution) has a uniform composition throughout.
A heterogeneous mixture has a non-uniform composition of the components.
There exist no boundary between the various components. It exists as one phase.
The components exist in the solution as distinct parts (phases).
A homogeneous mixture exists in all three states.
eg. Gas $\rightarrow$ Air
Liquid $\rightarrow$ Water + alcohol
Solid $\rightarrow$ Alloys
A heterogeneous mixture does not exist in all three states. There is no gaseous heterogeneous mixture.
Other examples are
Salt + Sulphur
Oil + Water

Homogeneous Mixture Examples

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A homogeneous mixture is a mixture in which the constituents are uniformly distributed throughout its volume and cannot be seen separately.

Example: If a spoon of salt is dissolved by stirring in a bowl of water, the salt dissolves. We can no longer see it. We can add one more spoon of salt. On stirring the salt dissolves and disappears. Thus the composition of the salt solution is not uniform. Such a solution in which the components cannot be seen and the composition is not fixed is called a homogeneous solution.

Other examples are milk, sugar solution, well water, ink etc.

Heterogeneous Mixture Examples

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In a heterogeneous mixture the mixture components are not mixed very well and by looking we can tell that it is a mixture. There is no chemical combination of the components of a mixture as there is with the elements that make up a compound.

A mixture of sand, salt and iron fillings is a heterogeneous mixture in which each constituent can be easily picked up by hand. Other examples of heterogeneous mixture are gun powder ( a mixture of carbon, sulphur and potassium nitrate), muddy water (a mixture of mud, sand and water), smoke (a mixture of carbon particles in air), chalk in water, dust in water, water and oil etc.