Reasons for Separating the Constituents of Mixtures

Organic chemistry is a fascinating branch of Chemistry Topics that focuses on the structure, properties, and reactions of carbon-based compounds.

Why do we need Seperate Mixtures?

If we observe some sugar and some soil (mitti) placed on two different sheets of paper with a magnifying glass, we will find that the colour, shape and size of all the particles of sugar are the same, but the soil contains particles of different colours, shapes and sizes. For example, the soil contains clay particles, some grass particles and even some dead insects, etc. Now, sugar which contains particles of only one kind is called a pure substance whereas soil which contains particles of different kinds is called an impure substance (or mixture). We can now define a mixture as follows :

A mixture is made up of two (or more) pure substances. The pure substances which are present in a mixture are called components of the mixture (or constituents of the mixture). The components of a mixture retain their original properties. So, a mixture shows the properties of all the substances present in it. For example, air is a mixture of gases such as oxygen, nitrogen, argon, carbon dioxide and water vapour, etc. So, air shows the properties of all its components. For example, oxygen supports the process of burning (or combustion) and air also supports the process of burning. All the mixtures are impure substances (because they contain more than one kind of particles).

Most of the things which we use in our day to day life are mixtures. Some of the mixtures around us are : Air, Sea-water, Rock salt, Sharbat, Milk, Tea, Coffee, Pond water, Tap water, Sugarcane juice, Jaggery (Gud), Soil, Rocks, Soft drinks and Petroleum. Most of the materials obtained from plants and animals are also mixtures. The main components present in some common mixtures are given below :

1. A cup of tea is a mixture of several components such as water, tea leaves extract, sugar and milk.
2. Milk is a mixture of cream in a watery liquid.
3. Sea-water is a mixture of water, common salt, and various other salts dissolved in it.
4. Wheat obtained from fields (after threshing) is a mixture of wheat grains and husk.
5. Petroleum (crude oil) is a mixture of various carbon compounds which make up fractions like petrol, kerosene and diesel, etc.

A mixture can be a solid, liquid or gas. For example, soil is a solid mixture, milk is a liquid mixture whereas air is a gaseous mixture. In some cases we can easily see the different substances (or components) present in a mixture. For example, the pulses bought from the market is a kind of mixture which contains tiny pieces of stone, etc. We can see the grains of pulses and the pieces of stone easily. In most of the cases, however, we cannot see the different substances (or components) present in a mixture. For example, sea-water is a mixture in which we cannot see the various salts which are dissoved in it. We will now discuss why the mixtures need to be separated into their components.

Reasons for Separating Mixtures into Their Components

The mixtures are separated into their components for various purposes, such as :

1. to remove an undesirable component,
2. to remove a harmful component,
3. to obtain the pure sample of a substance, and
4. to obtain a useful component.

All these reasons for separating mixtures into their components will become more clear from the following examples.

We make a cup of tea by boiling tea-leaves in water and then adding sugar and milk. After the tea has been made, we remove (or separate) the used tea-leaves from it before drinking it. Used tea-leaves are an undesirable component of the mixture called ‘tea’. These are separated by using a filter called ‘tea- strainer’. From this example we conclude that one of the reasons for separating a mixture is to remove an undesirable component from it.

We buy wheat, rice and pulses from the market. These foodgrains usually contain small pieces of stones and some insects, etc. These pieces of stone and insects are harmful to us. So, we separate the small pieces of stones and insects, etc., from wheat, rice and pulses before using them. From this we conclude that another reason for separating a mixture is to remove a harmful component from it.

Tap water contains some dissolved salts in it, so it is an impure substance or mixture. Though tap water is fit for drinking, it cannot be used for preparing medicines. This is because pure water (free from dissolved salts) is needed for preparing medicines. So, we separate the dissolved salts from tap water to obtain a pure sample of water called distilled water. This is done by the process of distillation. From this we conclude that a yet another reason for separating a mixture is to obtain a pure sample of the substance.

Petroleum oil is a mixture which cannot be used as such as a fuel in homes and vehicles, etc. We separate the petroleum mixture to obtain useful components like kerosene, petrol and diesel, etc. Now, kerosene is used as a household fuel whereas petrol and diesel are useful as fuels in vehicles. From this we conclude that a mixture is separated to obtain useful component (or components). Similarly, butter is a useful component which is separated from a mixture called ‘milk’. We will now describe the methods for the separation of mixtures.