Colloids Around Us: You must have seen solutions like ink, milk, blood, and soap solution. On looking at these solutions, we observe that they are homogeneous as we cannot see separate or different layers, but in reality, they are heterogeneous in nature. This confusion appears to us because the solution is not perfectly transparent as it is somewhat translucent. In this article, we will study in detail about a specific type of solution- Colloids and their properties and examples around us.

Study Applications of Colloids Here

What are Colloids?

Solutions are classified as the true solution, suspension, or colloids based on the size of the solute particles. A colloid is a type of solution in which the size of the solute particle ranges from \(1\) to \(1000\;{\rm{nm}}\). It is a heterogeneous system of two or more substances in which the size of the dispersed particles is greater than the size of the solute particles of a true solution but smaller than the size of the particles of a suspension.

Some other names of colloids are as follows:

1. Colloidal system
2. Colloidal state
3. Colloidal solution
4. Sol (SOL)

Components of Colloids

The medium of colloids is called the dispersion phase or dispersion medium, and its other component is called the dispersed phase. For example, in milk, water is the dispersion medium, and fats, proteins, sugar, etc., are the dispersed phases.

Classification of Colloids

The classification of Colloids are explained below:

On the physical state of the dispersed phase and the dispersion medium-

If the dispersion medium is solid, the colloid is referred to as a gel. If the dispersion medium is liquid or gas, the colloid is referred to as sol. An emulsion is a colloid in which both the dispersed phase and the dispersion medium are liquids.

On the basis of the nature of the interaction between the dispersed phase and dispersion medium-

• a. Lyophilic Colloids: Lyophilic colloids are those that exhibit a strong interaction between the two phases, as the name implies (liquid-loving or solvent-attracting).
• When gum, gelatin, and starch are mixed with a suitable liquid as the dispersion medium, they directly form colloidal sol, also known as a lyophilic sol.
• b. Lyophobic Colloids: ‘Lyophobic’ means ‘solvent hating,’ implying that there is little or no interaction between the two phases in these sols. Metals and their sulphides do not form colloidal sol when simply mixed with the dispersion medium. They cannot be made simply by combining the two phases.

On the basis of the type of particles of the dispersed phase-

• a. Multimolecular colloids: These are composed of a large number of molecules arranged in the form of aggregates, such as sulphur sol. 
• b. Macromolecular colloids: These colloids are made up of a single large molecule dispersed in a liquid, such as polythene.
• c. Associated colloids: These are colloids that behave as normal electrolytes at low concentrations but become colloids at high concentrations. This is due to the formation of aggregates known as micelles, which are found in soaps and detergents.

Properties of Colloids

The properties of colloids are explained below:

• Stability: Colloids are relatively stable in their natural state. The particles in the dispersed phase are constantly moving and remain suspended in the solution.
• Filterability: For filtration, colloids require specialized filters known as ultrafilters. They easily pass through ordinary filter papers with no residue.
• Appearance: Colloids are heterogeneous in nature because they have two phases, the dispersed phase, and the dispersion medium, but they appear to be a homogeneous solution. This is due to the fact that the suspended particles are so small that they cannot be seen with the naked eye.
• Colligative properties: These are the properties of a solution that depend on the number of moles of solute particles present in the solution, such as osmotic pressure, boiling point elevation, and so on. These colligative properties are of small order as compared to values shown by true solution at the same concentrations.
• Tyndall effect: The scattering of light by colloidal particles is known as the Tyndall effect. True solutions do not exhibit the Tyndall effect. Colloidal particles scatter and are illuminated because their dimensions are comparable to the wavelengths of ultraviolet and visible radiations.

• Brownian movement: Brownian movement refers to the zigzag motion of colloidal particles. This is due to the impact of the dispersion medium molecules on the molecules of the dispersed phase.

• Electrophoresis: It is the movement of colloidal particles towards their respective electrodes in the presence of an electric field. This is also referred to as cataphoresis—this aids in determining the charge of the colloid.
• Charge: Colloidal particles have a specific electrical charge. All colloidal particles in the colloidal solution have the same type of charge, whereas the dispersion medium has an equal but opposite charge. As a result, the charge on colloidal particles is balanced by the charge on the dispersion medium, and the colloidal solution is electrically neutral.

Emulsions

Emulsions are colloids that have both the dispersed phase and the dispersion medium in liquid form.

Types of Emulsions

• i. Oil in water: It is an emulsion with oil as the dispersed phase and water as the dispersion medium. For instance, milk and vanishing cream.
• ii. Water in oil: It is an emulsion with water as the dispersed phase and oil as the dispersion medium. As an example, consider cold cream—cod liver oil, butter, etc.

Emulsifying Agent

These are surface-active agents that are added to emulsions to help the two phases stay together. It acts on the interface to increase an emulsion’s kinetic stability, ensuring that the size of the droplets does not change significantly over time, thereby stabilising the emulsion.

Emulsifiers and emulsifying particles promote the dispersion of the phase in which they do not dissolve well. Proteins, for example, dissolve better in water than in oil and thus tend to form oil-in-water emulsions.

Water-in-oil emulsions are formed by emulsifiers that are more soluble in oil. Egg yolk, sodium phosphates, sodium stearoyl lactylate, and other similar substances are examples.

Demulsification

Demulsification is the process of separating an emulsion into its two distinct components, oil, and water. This can be accomplished by:

• i. Heating 
• ii.zing
• iii. Changing the pH
• iv. The phenomenon of electrostatic precipitation

Colloids Around Us

Following are the interesting examples of colloids:

• The blue colour of the sky: Dust particles along with water suspended in the air scatter blue light which reaches our eyes, and the sky appears blue.
• Fog, mist, and rain: When a large mass of air containing dust particles is cooled below its dew point, moisture from the air condenses on the particles’ surfaces, forming fine droplets. Because the droplets are colloidal in nature, they continue to float in the air as fog or mist. Clouds are aerosols that are made up of small droplets of water suspended in the air. Because of condensation in the upper atmosphere, colloidal droplets of water grow larger and larger in size until they fall as rain. Rainfall can occur when two oppositely charged clouds collide.
• Food articles: Milk, butter, halwa, ice creams, fruit juices, etc., are all colloids.
• Blood: A water-soluble respiration pigment-containing albumin protein. The pigment part contains albumin, which serves as the dispersed phase, and water serves as the dispersion medium. It’s a type of hydrosol.
• Soils: Fertile soils are colloidal in nature, with humus acting as a protective colloid. Soils absorb moisture and nourishing materials due to their colloidal nature.
• Formation of delta: River water is a colloidal clay solution. A variety of electrolytes can be found in seawater. When river water meets seawater, the electrolytes in the seawater coagulate the colloidal solution of clay, causing its deposition and the formation of the delta.

Applications of Colloids

• Medicines: Colloidal medicines are more easily absorbed by body tissues and thus more effective.
• Soap’s cleaning action: Soap solution has a colloidal structure. It removes dirt particles through adsorption or by emulsifying greasy matter that has adhered to the cloth.
• Water purification: Certain electrolytes, such as alum, can be used to precipitate colloidal impurities in water. Impurity negatively charged colloidal particles are neutralised by the \({\rm{A}}{{\rm{l}}^{3 + }}\) ions and settle down, allowing pure water to be decanted off.
• Rubber industry: Latex is a colloidal solution of negatively charged rubber particles used in the rubber industry. Rubber can be made from latex by Coagulation. Rubber-plated articles are made by depositing negatively charged rubber particles over the article which needs to be rubber plated, which is an anode in a rubber plating bath.
• Sewage disposal: Because colloidal particles of dirt, mud and other materials carry an electric charge when sewage water is passed through plates with high potential, the colloidal particles coagulate due to electrophoresis, and the suspended matter is removed.
• Artificial rain: Spraying oppositely charged colloidal dust or sand particles over a cloud can produce artificial rain. The colloidal water particles in the cloud will be neutralised and coagulate to form larger water drops, resulting in artificial rain.
• Froth floatation process: The concentration of ore by froth floatation process in metallurgical processes is based on the treatment of powdered ore with oil emulsion. The valuable ore particles form foam, which rises to the surface and is skimmed off.

Summary

In this article, we studied that colloid is a heterogeneous solution that appears homogenous. It is a type of solution in which the size of the solute particle ranges from \(1\) to \(1000\;{\rm{nm}}\). We also studied the different classifications of colloids based on the physical state, nature of substance, and types of particles. Now we know some of the important properties of colloids like the Tyndall effect, Brownian movement and Electrophoresis, and also the applications of colloids in various fields.

FAQs on Colloids Around Us

Q.1. What are colloids around us?
Ans: The following are some examples of colloids that we commonly see.
i. Liquid aerosol- smog, fog, aerosol sprays.
ii. Solid aerosol- smoke and dust.
iii. Foam- shaving cream and whipped cream.
iv. Emulsion- mayonnaise and milk.
v. Gels- butter and jelly products.
vi. Sols- Ink and paints.
vii. Solid sols- medicines.

Q.2. What are the five types of colloids?
Ans: Aerosols, foams, emulsions, sols, and gels are the five primary types of colloid solutions that can be created by mixing different components. Some of these colloids are found in nature, while others are created by humans.

Q.3. What are the uses of Colloids in our daily life?
Ans: Some of the uses of colloid are as follows:
i. Colloids are thickening agents used in lubricants, lotions, toothpaste, coatings, and other commercial items.
ii. Colloids are important in the production of paints and inks. Gel ink is used in ball-point pens (liquid-solid colloid).
iii. The majority of the medications are colloidal in nature.

Q.4. What are the properties of colloids?
Ans: Some of the properties of colloids are as follows:
i. It is a mixture that is heterogeneous.
ii. Particles are too small to be seen with the naked eye.
iii. They scatter light travelling through them, allowing the path of the light to be seen.
iv. When left undisturbed, they do not settle down.
v. The ordinary filtration procedure will not be able to separate them.

Q.5. What is the major difference between lyophilic and lyophobic sols?
Ans: There is a strong connection between the dispersed phase and the dispersion medium in lyophilic sols, which makes them highly stable and resistant to Coagulation. Lyophobic sols have weak Van Der Waals forces of attraction between the dispersed phase and the dispersion medium, which are irreversible and easily coagulate.