Separation of Mixtures

The name of todays topic is Separation of Mixtures for ICSC chemistry class 6 .The things that we see in our day to day life are divided into two main categories i.e living and non-living. The non living things mainly consist of elements, compounds and mixtures.

Separation of Mixtures

Elements and compounds are pure substances while mixtures are not.Two or more elements or compounds mix together in any ratio to form mixture. These substances don't react chemically and don't lose their physical properties.For example - air, sea water, cold drinks etc. Air is a mixture of many gases, dust particles and water vapours. Let's see the difference between a mixture and a compound with the help of an activity. Take two elements such as sulphur and iron fillings in any ratio and mix these two elements. If you will take a magnet near this mixture the iron fillings will get attracted towards the magnet and both iron and sulphur can be separated from each other. So it is possible to separate these elements from the mixture because they don't lose their physical properties and don't react chemically. Now if we will heat this mixture of iron and sulphur the compound formed is known as iron sulphide.In iron sulphide, iron and sulphur lose their individual physical properties as they react chemically to form this compound.

Difference between mixture and compound

Need to separate the components of the mixture Some mixtures that are found in nature are useful for us. Such as fruits and vegetables are good for our health and keep us away from diseases. But some mixtures are harmful for us that need to be separated. These include impure water, pulses, rice, wheat etc which consist of dust, small insects, stones etc. It is not possible to separate all these substances by the same method. So different methods of separation are adopted depending on the size, shape and colour of the particles and various other factors. It is very important to obtain pure substances from the mixtures to use them at homes, in factories and research purposes. Different methods used for separating mixtures are -

1.Handpicking

2.Sieving

3.Winnowing

4.Magnetic separation

5.Sublimation

6.Sedimentation and Decantation

7.Filtration

8.Evaporation

9.Distillation

10.Crystallization

Ways to separate solid-solid mixtures

1.Handpicking - This method is used to separate the undesirable or unwanted component from the desired component which we want to obtain.This method is used generally when the undesirable component is in lesser amount than that of the desired component. The handpicking method of separation usually depends upon the size, shape and colour of the particles. For example - to separate small stones from pulses, rice etc.

Separation technique

Due to the difference in the size, shape and colour of the undesirable particles they can be picked up by hands easily.

2.Sieving - This method is used to separate the solid-solid mixtures in which the size of the components are too small and can't be picked up manually with hands.In this method a sieve is used to separate the components. This method is used by jewellers to separate pearls of different sizes, to separate impurities from flour, to separate sand or mud from larger particles.

Sieve used in the sieving method

Separation technique

In this method of separation, the mixture to be separated is taken on a sieve. On shaking the sieve the smaller particles pass through it while the bigger particles are left behind on the sieve.

3.Winnowing - This method is used generally when the desired components are heavier than the undesired components.This method is used generally to separate husk or chaff from grains such as rice, wheat, oats etc.

Separation technique

The mixture to be separated is thrown from a height. The heavier particles settle down while the lighter particles are blown away by air.

4.Magnetic Separation - This method is generally based on the property of the elements to get attracted towards the magnet such as iron. Impurities are removed from iron by using this method in factories.

Separation techniques

Big electromagnets are fitted to a crane to separate scrap iron from impurities in big factories.

5.Sublimation - In this method, a solid is converted directly into its vapours upon heating the mixture. This method is used generally to separate the mixture in which a component of the mixture sublimes upon heating.On sublimation, the component escapes as vapours while the component that doesn't sublime is left behind. The vapour is again converted into solid upon cooling. Some examples of solids that can sublime are naphthalene, camphor, ammonium chloride etc.

Separation technique

A mixture of solids is taken in an evaporating disk placed upon a wire gauze on a tripod stand and is covered by an inverted funnel closed by a cotton plug. Upon heating one of the solid present in the mixture changes into vapours and rises up by the process of sublimation.These vapours are converted back into solid on cooling.

Ways to separate solid-liquid mixture

6.Sedimentation and Decantation

This method is generally used to separate the mixture of solid and liquid in which the solid particles are heavier than the liquid and are insoluble in the liquid.This method of settling down of heavy and insoluble solid impurities at the bottom if left undisturbed for sometime is known as sedimentation. The solid component settled at the bottom is called as sediment while the clear liquid present above is known as supernatant liquid.For example a mixture of mud and sand is separated using this technique.

Separation techniques

Take a mixture of sand and water in a beaker. Keep it undisturbed for sometime.After sometime the heavy and insoluble particles settle down at the bottom.

Decantation - The process of sedimentation is followed by the process of decantation.

Separation technique

In the process of decantation, the clear liquid obtained in the process of sedimentation is poured out very carefully without disturbing the sediment which is settled down.

7.Filtration - If in a solid-liquid mixture, the solid is insoluble in the liquid then it can be separated by this method. So the process in which insoluble solid particles are separated from the liquid with the help of a filter is known as filtration.The filter used in this process may be a muslin cloth, strainer, cotton layer or a layer of sand. In laboratories, a filter paper is used in the process of filtration. This process is used to obtain clear water from the mixtures of sandy or muddy water, mixture of water and chalk.

Separation technique

In this technique, the liquid to be cleaned is passed through the filter i.e strainer, muslin cloth etc. The liquid passes through it but the insoluble impurities don't pass and are left behind. In laboratories, a cone of filter paper is made by folding it twice which is kept on a funnel placed above a beaker. The liquid to be filtered is passed from the first beaker to the second beaker through this filter paper. The residue is left on the filter paper while the clear liquid known as the filtrate is obtained after passing the dirty liquid through the filter paper.

8.Evaporation - The process of changing liquid into vapours by heating or exposing to air is called evaporation. This method is generally used to separate salt from the mixture of water.So this method helps to obtain salt from sea water.

Separation technique

Take a mixture of salt and water. Heat it. The water will start evaporating . Heat it until all the water is evaporated and only salt is left behind.To obtain salt , sea water is evaporated by collecting it in shallow beds.

9.Distillation - This process of simple distillation is used to separate liquids from non-volatile solids (solids that don't change into vapours easily as their boiling points are higher than 100°C)a mixture in which the two miscible liquids don't decompose on heating and have different boiling points. For example - a mixture of salt and water, a mixture of acetone and water.

Separation techniques

In this process, a liquid is heated to its boiling point and its vapours are transferred to a condenser. These vapours are then condensed back or changed back into liquid This liquid is collected in a receiving flask.

10.Crystallization - Crystallization is a process in which pure substances are obtained by the process of formation of crystals.For example - Harvesting of salt, to obtain alum crystals.

Separation technique

Add enough solvent to a solid, impure compound so that it can dissolve in it completely.On cooling down, the solvent will not be able to hold all the solute particles and they start to form crystals leaving the solvent.

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