Separation techniques

 Introduction:  

The mixture is nothing but the combination of two or more substances where every substance retains its own chemical identity. Like air, salt, and sugar solutions are a few examples of mixtures. Mixtures can be categorized into homogeneous and heterogeneous mixtures. 

Homogeneous mixtures have a uniform composition throughout all substances present in them. The mixtures that are not uniform all through are called heterogeneous mixtures. 

The various constituents of the mixture have different physical properties such as density, solubility, size of particles, boiling point, behaviors towards the magnet, volatility, etc. The difference in the physical properties of components is used to separate them from the mixture. We learned a few separation techniques in the previous classes, such as sublimation, magnetic separation, crystallization, filtration, etc. 

This session lets us learn some more techniques used to separate the mixtures. 

Separation techniques can separate two different states of matter, such as solids and liquids. Separation is an important asset to purify components of interest from a mixture. 

1. Mixture of Solid and Liquid 

The following processes separate a mixture containing solid and liquid. 

1. Chromatography 

2. Centrifugation 

3. Distillation 

We have learned about filtration and evaporation in our previous classes. Evaporation separates the solid substance dissolved in water (or any other liquid). At the same time, filtration separates insoluble substances from a liquid by using filter paper. In this session, let us learn more about the other separation techniques like chromatography, centrifugation, and distillation. 

1. Chromatography 

Chromatography is the special technique used to separate two or more dissolved solids that are present in very small quantities (that dissolve in the same solvent). 

The simplest type of chromatography is paper chromatography. 

Principle of Chromatography: 

1. Septation is based on the fact that though two or more substances are soluble in the same solvent, their solubilities may differ. 

2. The component, which is more soluble, rises faster and gets separated from the mixture. 

3. A special type of chromatographic or ordinary filter paper is taken in this method. 

4. A line is drawn with a pencil near the bottom edge of this paper. A mixture drop is placed on the filter paper above the bar. The article is then dipped inside the solvent and taken in the beaker such that the line drawn on the form is above the level of the solvent. 

5. A filter paper acts as a stationary phase while the solvent acts as a mobile phase. 

Let us perform an activity to understand how this technique can be used. 

Activity: Separating different colors of dye from black ink 

Ink has water as the solvent, and dye is insoluble(solute). Pigment in ink is made of different colors mixed.  

Procedure: 

1. Take a thin strip of ordinary filter paper.  

2. Draw a line on it using a pencil (about 3 cm from the bottom of the paper). 

3. Put a small drop of the given ink at the center of the line using a sketch pen. 

4. Let it dry. 

5. Now take the beaker filled with some water. 

6. Lower the filter paper in a beaker until the ink drop on the paper is just above the water level. 

7. As the water rises to the top of the filter paper, remove the paper strip from the jar and dry it. 

Observations: 

1. There is a significant rise in the color from its initial point. 

2. Different color of ink is also visible at different heights. 

Results: 

The chromatogram obtained shows three different colored spots on it. 

The given sample of black ink has three different dyes mixed in it. 

Note: chromatogram is a visible record (such as a graph) showing the result of separating the components of a mixture by chromatography. 

Reason: 

When water rises up on filter paper, it takes the dye of ink along with it. 

• The component which is more soluble in water rises faster and is seen at higher position 
• The component which is less soluble is seen below at lower position 

Application of Chromatography 

• It is used to separate the solution of different colored substances. 

• Also, it is used for separating drugs components from the sample of blood. 

• It is utilized to check the purity of medicines. 

• It is also used to detect the contaminants in drinks and foods. 

• It is also employed to separate pigments from natural colors. 
  
  

2. By Centrifugation: 

Centrifugation is used to separate the insoluble substances from a liquid where normal filtration does not work well.  

It is based on the size, shape, and density of the particles, viscosity of the medium, and the speed of rotation. 

Principle: The heavier particles are forced to settle at the bottom, and the lighter particles stay at the top when spun rapidly. 

Process: 
The mixture of suspended particles is taken in the test tube. 

The test tube is placed in a centrifuge machine and rotated rapidly for some time. 

As the mixture rotates rapidly, a force acts on the heavier suspended particles in it and brings them down to the bottom of the test tube. 

The clear liquid, being lighter, remains on the top. 

Example: Separating cream from milk, separating butter from cream. 

Procedure: 

• The centrifugation process is used in diaries to separate cream from milk. 
• The milk is put in a closed container in a big centrifuge machine. 
• The centrifuge consists of a centrifuge tube holder called the rotor.  

• When the device is switched “on,” the milk is rotated at a very high speed in its container. As a result, milk separates into “cream” and skimmed milk. 
• The cream being lighter, floats over the skimmed milk. 

Application: 

• It is used to separate the clay debris suspended in water very swiftly through centrifugation. 

• It can be used to separate cream from milk by centrifugation. 

3. It is used in diagnostic laboratories for blood and urine tests. 

4. It is used in washing machines to squeeze water from wet clothes. 
   
   

3. Distillation 

In the distillation, water vapors convert into volatile liquids, and then they separate through selective boiling.  

It is used to separate the liquids which have different boiling points.  

Distillation can be represented as follows: 

Steps Involved in the distillation process: 

1. The mixture is heated until one of the components boils (turns to a vapor). 

2. The vapor is then fed into a condenser, which cools the vapor and changes it back into a clear liquid. 

3. This clean liquid is called the distillate. 

4. The solid non-volatile substance in the distillation flask is called the “residue”. 

5. The mixture is heated until one of the components boils (turns to a vapor). 
   
   

Uses of Distillation 

Distillation is used for many industrial processes. 

It is used to produce gasoline, distilled water, xylene, alcohol, paraffin, kerosene, and many other liquids. Gas may be liquefied and separated. 

It is also used to separate the mixture of gases.  

For example, nitrogen, oxygen, and argon are distilled from the air. 

Types of Distillation 

Distillation can be divided into four types.  

1. Simple distillation  

2. Fractional distillation 

3. Steam distillation 

4. Vacuum distillation
   
   

1. Simple distillation: 

Simple distillation is used to separate mixtures consisting of two or more pure liquids with enough difference in their boiling points.  

The separation of a mixture of liquids is based on the boiling point of these liquids. 

It is a purification process where the liquid mixture is heated to form vapor first and then cooled to recover the liquids. 

Example: Mixture of acetone and water 

Separation of the mixture of acetone and water by distillation 

Equipment Required: 

A variety of acetone and water 

Distillation flask 

Thermometer 

Condenser 

Beaker 

Steps Involved: 

1. Take a mixture of acetone and water in a flask. 

2. Heat the flask. 

3. Monitor the temperature with the help of a thermometer. 

4. When the boiling point of acetone is reached, it converts into vapor. 

5. However, water is left in the flask as it has a higher boiling point. 

6. The acetone vapors flow into the condenser, where it gets cooled and converts into liquid again. 

7. The liquid acetone is stored in the beaker, and water remains in the flask.  

Note: The boiling point of water is 100 ℃, Boiling point of acetone is 56 ℃. 

Limitation: This method cannot be used when there is less difference in the boiling point of different components. 

Applications: 

A mixture of common salt and water can be separated by distillation. 

It is also used to obtain drinking water from seawater. For distillation of alcohol.