What is a Colloidal Solution? What are some examples : Class 12 Chemistry
Before we go to explain what is Colloidal solution let us understand the definition for Colloids. A colloid is nothing but a mixture where one of the substances in it is dispersed and suspended through another liquid. Now one unique thing here is one of the substance of the mixture will have insoluble particles in it which are microscopically dispersed. Some of the particles must be dispersed in the liquid so to say and we can here take the example of aerosols and gels.
Now the term Colloidal solution will describe that there is an overall mixture which is unambiguous. The Colloids have dispersed and phase which is continuous. The medium where it is suspended is continued and the suspended particles are said to be in dispersed phase. The particles which are dispersed are known to have diameter of about 1 nanometre to 1 micrometer. Some of the colloids are translucent because of the Tyndall effect. Tyndall effect is the scattering of light particles by the particles in the particular colloid. However some other colloids maybe opaque or even have a slight colour. The colloidal suspension has been long time study for interface and colloid science. This field of science was initially introduced by Italian chemist FransescoSelmi and there were further investigations since 1861 by others.
Here let us consider some scenarios. We have a dispersed phase and a dispersion medium.
- Dispersed phase is GAS and dispersion medium is also GAS. The result is that there are no suchcolloids. Exception might be Helium maybe and it can have the quality of being miscible. That is they can mix in all proportions forming a homogenous mixture.
- Dispersed phase is GAS but dispersion medium is LIQUID. Here we have Foam. Examples are Whipped cream, shaving cream etc.
- Dispersed phase is GAS but dispersion medium is SOLID. Here we have solid foam. Example- Styrofoam, pumice etc
- Dispersed phase is LIQUID and dispersion medium is GAS- Here we have Liquid Aerosol. Eg- fogs, clouds, mist, etc
- Here both the dispersed phase and dispersion medium are LIQUID. Then it becomes liquid crystal or emulsions. Eg- Milk, cream, latex , mayonnaise etc
- Here we have dispersed phase is LIQUID but dispersion medium is SOLID. Then we get GEL. Eg- Agar, Gelatineetc
- Now we consider last three scenarios- beginning with – dispersed phase is SOLID but dispersion medium is GAS. Then it becomes Solid Aerosol. Eg- Smoke, ice cloud etc.
- Next is dispersed phase is SOLID but dispersion medium is LIQUID. Then we have SOL or suspension. Example are – pigmented ink etc
- Last is SOLID is both dispersed phase and dispersion medium- Then we have SOLID SOL. Eg- Cranberry glass.
Now Colloidal Solution may also be classified into the following types:
- FOAM: This is a solution of a gas in a liquid and the substances being dispersed will be the Gas. The fluid then becomes frothy and foamy.
- EMULSIONS: When one liquid is dispersed into another and forms a continuous one. Milk is an example of this.
- SOL: A sol is when a solid is evenly dispersed into a liquid. Eg- paint etc
- HYDROCOLLOID: More complex form of a colloidal solution. Here a fluid of a precise material is dispersed into Water. Eg- Gelatine. The main idea here is to increase the texture of the food material.
- REVERSIBLE OR IRREVERSIBLE COLLOIDS– Here two materials can be divided and is called Reversible Colloids whereas the Irreversible Colloids is where this is not possible.
In our day to day life we can see in our surroundings that some colloidal solutions can be used as transporters. Many different types of particles can attach themselves to the water particles hence being suspended and be used to transport. Not necessary it will always yield good results – sometimes this can be hazardous because they can convey radioactive materials through water. In the field of medicine sometimes they ca be used for blood conditions.
They are also used to control colloidal osmotic pressure.
In the above diagrammatic representation we can see the particle behaviour or size in three of the solution types- True solution, Colloidal and suspension.
What are Colloids compared with solution- A colloid has a dispersed phase whereas the solution, the solvent and solute have only one phase. In colloid particles are bigger. Eg- In Milk the colloidal particles are fat globules rather than individual fat molecules.
Colloidal particles often carry electric charges and can either repel or attract each other. The charges of both of them are continuous and are in dispersed phase. There are steric forces acting on it and in solutions they have non absorbing polymer and these can modulate forces thus producing the additional steric repulsive forces and either is an depletion of force between them.
Refer: Surface Chemistry from Class 12 Chemistry– Find All the Questions & Answers