Lyophobic Colloids

Lyophobic is a type of colloid and  a heterogeneous mixture. It is a stable solution. Lyophobic is a solvent repelling solution. Lyophobic is an important topic in Chemistry. Colloids have various kinds based on the state and interaction between the dispersed medium and the dispersion phase. In this article, we will discuss the concept of colloids, lyophobic sol., and topics related to it.

Let us start with the topic of what are colloids:

What are Colloids?

A colloid is a heterogeneous mixture where very small particles are dispersed through the dispersion medium. Colloids can be classified into three parts. They are as follows:

Sol – solid in liquid

Emulsion – liquid in the liquid

Gel – liquid in solid

Based on the interaction between the dispersion phase and dispersed medium, sols are further classified into

1. Lyophilic sols or lyophilic colloids – It means solvent-loving. They are called hydrophilic if water is used as a dispersion medium.
2. Lyophobic sols or lyophobic colloids – It is meant by solvent-hating. They are known as hydrophobic if water is used as a dispersion medium. In lyophobic colloids, the colloids are not readily prepared because the dispersed phase does not have an affinity for the dispersed medium. They are also called irreversible sols because they can not be reformed in the simple way of adding dispersion medium after precipitation. They are not stable. But adding electrolytes, heating, or shaking, they can be coagulated easily. This type of colloids can be formed by using some specific methods, and it needs a stabilising agent. Some examples of lyophobic colloids are metals and their insoluble compounds like sulphides, oxides, etc. In these sols, there is very little or no interaction between the dispersed phase and the dispersion medium, which means the dispersed phase has less affinity for the dispersion medium.

Gold, arsenic, silver halides, sulphide, etc., are some examples of it. As these colloids are stable, many classical investigations are based on the stability of colloidal solutions. Research has suggested that the stability of these colloids is connected with their electric charges. Several types of research have been done in the past to discover the origin and magnitude of the electric charge on the particles and the nature of the electrical double layer. An electrical double layer exists in salt solutions. However, some quantitative and semi-quantitative explanations are given on the concept of coagulation and the rule of Hardy and Schulze. According to these explanations, precipitation needs ionic concentration, which diminishes quickly with the charge of the effective ion. A complete and satisfactory theory is still pending on this.

Ferric Hydroxide Sol

When Ferric hydroxide is treated with water, it forms lyophobic sols. Ferric hydroxide sol is made by the hydrolysis of ferric chloride with the boiling of distilled water.

The particles of ferric hydroxide are made by the hydrolysis reaction, which passes through agglomeration to yield bigger particles of colloidal dimensions. These particles takeFe3+ ions from the solution to yield a positive charge to the sol particles. The charge on the sol particles gives stability to sols. During hydrolysis, hydrochloric acid is produced, which should be removed from the sol as it destabilises the sol. It can be removed from the sol by using the dialysis process. If we don’t remove this from the sols, they will not be stable.

Preparation of colloids-

Colloids can be prepared by using various methods, including physical and chemical methods. However, there are two main methods of preparation of colloids-

• Larger colloidal particles are formed by condensation of small dissolved molecules through condensation, precipitation, or redox reactions
• Dispersion of large particles (droplets) to the colloidal dimensions by spraying, milling or by using techniques of shear (shaking, high shear mixing, or mixing)

Chemical methods of preparation of colloids

Lyophobic colloidal solutions can be prepared by using many chemical techniques. Some of which are-

1. Oxidation technique- oxidation means combining a solution with oxygen. An aqueous solution of sulphur dioxide is passed through a colloidal solution of Sulphur. It can also be obtained by passing the gas through a solution of an oxidation agent like bromine water with nitric acid.

     SO₂ + 2H₂S → 2H₂O + 3S

1. Reduction technique- The other technique of forming colloidal solutions of metals like gold, silver, etc., includes the use of a reducing agent for reduction of the solutions of the metals. Stannous chloride is an example of a reducing agent.
2. Hydrolysis technique- it includes the use of boiling water. Ferric chloride is a reduced solution that involves the use of boiling water.

    FeCl₃ + 3H₂O → Fe(OH)₃ + 3 HCl

 3.Double decomposition technique- We obtain a solution of arsenious chloride on passing hydrogen sulphide through a solution of arsenious oxide in distilled water.

   As₂O₃ + 3H₂S → As₂S₃ + 3H₂O

Difference between lyophilic colloids and lyophobic colloids-

Conclusion

There is a detailed discussion of lyophobic colloidal solution (lyophobic sols). It is also called a hydrophobic solution. They are also irreversible sols. The definition of dialysis, dispersed phase, dispersion medium is also given above.