Colloids

Colloids or Colloidal Solution is a type of mixture in which insoluble components are suspended on a microscopic scale in some another component. Colloids are essential components in the daily lives of the common man, as we use or consume colloids and we even don’t know. From Jellys to Mayonese to the majority of beauty products, are some forms of colloids. Thus, understanding colloids will help us understand these things we use on a daily basis but don’t know about. In this article, we will learn about colloids in detail including their classification, properties, preparation method, and applications.

Colloids Definition

A solution in which the size of solute particles is intermediate between those in true solution and suspension is called Colloids. Simply, colloids are the mixtures where one substance is split into minute particles which are dispersed throughout a second substance. e.g. Soap solution, milk, blood, etc are some of the examples of colloids.

Colloids (also colloidal solutions or colloidal systems) are mixes of microscopically distributed insoluble particles of one material floating in another. A colloid’s suspended particles can range in size from 1 to 1000 nanometres (or 10^-9 meters). Generally, in colloids, the component which is in the minority is the dispersed phase and the majority component is called the dispersion medium. For example, in milk fat is a dispersed phase that is distributed in a dispersion medium i.e., water.

The suspended particles in a combination must not settle for them to be classed as a colloid (in the manner that the particles of suspensions settle at the bottom of the container if left undisturbed). Colloidal solutions are known to show the Tyndall Effect, a phenomenon in which light beams impacting on colloids are dispersed as a result of interactions between the light and the Colloidal component.

Classification of Colloids

Colloids can be classified into different classes based on the different properties taken into consideration the different parameters such as the physical states of mediums and phases, the interaction of particles, or different properties of medium and phase particles.

Classification of Colloids Based on Physical States

Based on the physical states of the dispersion medium and dispersed phase, colloids can be classified into many types, some of those classifications are Sols, Emulsion, Foam, Gels, and Aerosols. The details of these types are as follows:

• Sol is a colloidal suspension when the dispersion medium is solid and the dispersion phase is liquid. Paints, inks, gold sol, silver sol, muddy water, starch, etc. are all examples of Sol.
• In Emulsion colloidal suspension, both Dispersion Medium as well as Dispersed Phase, are liquids, and particles of the medium are not soluble in the dispersed phase. For example, we know, that oil and water are insoluble in each other so the oil in water or water in oil are both examples of colloids when mixed together using some methods. Milk and butter are the most common examples of emulsion. 
• Aerosols are the solution in which very minute fine particles of solid particles are dispersed into a gas. For example,  Smoke, dust storms, exhaust from industries and automobiles, etc. 
• Gels are colloidal solutions in which minute liquid droplets are dispersed into a solid dispersion medium, it is also called solid emulsion. For example,  Jellies, Cheese, Curd, shoe polish, etc.
• Foam is a colloidal solution in which a liquid dispersion medium is suspended in a gaseous dispersed phase. For example, Pumice stone, rubber, cake, etc.

Other than the above-mentioned types classification, a complete table for each different combination of dispersion medium and the dispersed phase with examples, are given below:

Dispersion Medium	Dispersed Phase	Type of Colloid	Examples
Solid	Solid	Solid sols	Colored Glass, Gemstones,  Rock Salt, some alloys.
Solid	Liquid	Gels	Jellies, Cheese, curd,  shoe-polish.
Solid	Gas	Solid foam	Pumice stone, rubber, cake.
Liquid	Solid	Sol	Paints, inks, gold sol, silver sol,  muddy water, starch.
Liquid	Liquid	Emulsion	Milk, butter, cod liver oil
Liquid	Gas	Foam	Soap lather, soda (CO2 is dissolved  in water) water, whipped cream
Gas	Solid	Aerosol	Smoke, dust storms, and exhaust from  industries and automobiles.
Gas	Liquid	Aerosol	Fog and Mist

Classification of Colloids based on Interaction

Based on the interaction between particles of colloids, these can be classified as follows:

• Lyophilic colloids are colloidal solutions where the particles of the dispersed phase have a strong affinity for the particles of the dispersion medium. Examples include gum, starch, gelatin, and proteins.
• Lyophobic colloids are colloidal solutions where the particles of the dispersed phase have a weak affinity for the particles of the dispersion medium. Examples include silver sol, ferric hydroxide sol, and arsenic sulfide sol.

Classification of Colloids based on Properties of Sol Particles

Based on the properties of sol particles, colloids can be classified as follows:

• Multimolecular colloids are colloids formed when small molecules or atoms combine to form a species that falls within the colloidal size range. For example, a sulfur solution consisting of thousands of S₈ particles.
• Macromolecular colloids are biomolecules such as enzymes or proteins that are larger in size and form colloids when properly dispersed. Examples include rubber, cellulose, and starch.
• Associated colloids are substances whose molecules are amphiphilic, meaning that they contain both a non-polar hydrophobic part and a polar hydrophilic part.

Classification Based on Dispersion Medium

Based on the specific dispersion medium, the following colloids are defined:

• Hydrosols are colloids in which water is the dispersion medium. Examples include starch colloids.
• Alcosols are colloids in which alcohol is the dispersion medium. Solutions containing ethanol and methanol are examples of alcosols.
• Acrosols are colloids in which air is the dispersed phase. Examples include mist colloids.

Preparation of Colloids

The stable colloids are known as lyophilic sols, in these, the strong forces of attraction take place between the dispersed phase and dispersion medium. Some of the major methods to prepare colloids are as follows:

Condensation Method 

Small solute particles are condensed in this process to create a dispersed phase particle.

• Oxidation: We can obtain colloidal Sulphur by passing oxygen gas through the solution of Hydrogen Sulphides. HNO₃, H₃Br₂, etc are used as oxidizing agents in this process.

2H₂S + O₂  ⇢  2H₂O + 2S

• Reduction: In the process, suitable reducing agents such as formaldehyde, hydrogen peroxide, stannous chloride, etc are reacted with the aqueous solution of these salts to obtain metals like gold, silver, and platinum in the colloidal state.

2AuCl₃ + 3SnCl₂  ⇢  3SnCl₄ + 2Au

• Double Decomposition: In this process, hydrogen Sulphide is passed through a cold arsenic oxide solution in water and a solution of arsenic Sulphide is obtained.

As₂O₃ + 3H₂S   ⇢  As₂S₃ + 3H₂O

• Hydrolysis: Salt solutions are hydrolyzed by boiling their respective dilute solutions. For example, ferric hydroxide is obtained by hydrolysis of its corresponding salt.

FeCl₃ + 3H₂O ⇢ Fe(OH)₃ + 3HCl

Dispersion Methods

Large particles of material (suspension) are broken down into smaller particles using these procedures. The procedures listed below are used:

• Mechanical Dispersion: In this method, the substances are grounded to coarse particles and mixed with a dispersion medium to get a suspension. Then, it is ground in a colloidal mill consisting of two metallic dyes rotating in opposite directions. This method is used to obtain colloidal solutions of black ink paint varnished dyes, etc.
• Electrical or Bredig’S Arc method: In this method, the metal to be changed into solution is made as two-electrode which is immersed in a dispersion medium. An electric arc is used between the electrodes and ice to keep the dispersion medium cool. Here, the excessive amount of heat gives a colloidal solute substance.
• Peptization: The process of changing a freshly prepared precipitate into a colloidal solution is called peptization. A small amount of electrolyte is added as a peptization agent. Some of the important peptizing agents are electrolyte and sugar gem gelatin. For example, a freshly prepared ferric hydroxide can be changed into a colloidal solution through this method by shaking it with water containing FeCl_3.

Fe(OH)₃ + FeCl₃ → (Fe(OH)₁ Fe)⁺³ + 3Cl^–

Properties of Colloids

There are many physical and chemical properties colloids have, some of those properties are as follows:

• As the size of particles is very small (1-1000 nanometers), they can’t be filtered using the basic filtration method. To filter colloids, we need more specialized filtration methods, such as ultrafiltration or centrifuge.
• Colloids are very stable. and when left untouched for long periods it doesn’t show the sign of sedimentation or precipitation.
• Colloids are heterogeneous mixtures, where the dispersed medium is suspended in the dispersion phase in nor uniform arrangement.
• Despite the heterogeneous nature of colloids, they seem to have a homogenous appearance. This is because the particle is very small in colloids which can’t be seen by the naked eye.

Tyndall Effect: The Optical Properties of Colloidal Solutions

Colloids show a phenomenon known as the Tyndall effect, which John Tyndall identified in 1869. When we shine a bright converging beam of light through a dark colloidal solution, the path of the beam is lit and we can see the path. This is due to the scattering of light by the Colloidal particles, and this is referred to as the Tyndall effect, and the lighted route is called the Tyndall cone.

Brownian Motion: The Mechanical Properties of Colloidal Particles

The Brownian Motion is a characteristic of scattered particles in a colloidal solution, when a colloidal solution is examined via an ultramicroscope, the colloidal particles may be seen moving in a zigzag pattern.

These colloidal particles are constantly bombarded from all directions by the moving molecules of the dispersion medium. Thus, this gives momentum to the particles, causing them to travel ahead and collide with another particle. Collisions cause the colloidal particle to travel in a random zigzag pattern, and this zigzag pattern motion is called Brownian Motion.

Application of Colloids

Colloids have many applications in various industries, medicine, and domestic settings, including:

• In food: Colloidal systems are found in various food items like syrup, halwa, and soup.
• In medicine: Colloidal silver (Argyrols) is used as an antiseptic for eye infections.
• In air purification: Cottrell precipitator air purification technique uses coagulation of solution particles to remove dust or smoke particles from the air.
• In leather refinishing: Tanning of leather is done by immersing animal skins in a tannin solution with the opposite charge of the animal skin. This process causes particles to agglomerate and the skin to harden.

Sample Questions on Colloids

Question 1: Why is Milk a colloid?

Answer:

Due to the charged gap particles that remain suspended in the liquid, milk is a colloid. Milk is a colloid, despite having the appearance of being a homogeneous mixture, since it contains tiny globules of protein and fat that do not separate apart after standing due to the (often negatively) charged particles.

Question 2: What are the changes that may occur in a substance or matter?

Answer:

The changes that occur in the matter are physical and chemical changes. The physical changes are about changes in the state of matter and other external factors whereas, chemical changes are concerned with the chemical composition of the matter.

Question 3: What precautions should be taken during the dialysis process?

Answer:

During the process of dialysis, the distilled water in the container should be frequently changed to prevent the accumulation of crystalloids. Otherwise, the impurities will get diffused back.

Question 4: What is the application of colloids in industrial products?

Answer:

The application of colloid in industrial products are as follows:

1. Colloids are used as a thickening agent for the products like lubricants, lotions, toothpaste, etc.
2. It is also used in manufacturing inks and paints.
3. It is used in medicines as an antiseptic.
4. And, as stabilizers in food industries to manufacture foods items like jam, ice cream, etc.

Question 5: Which substance is used to reduce the pore size of filter paper for ultrafiltration?

Answer:

As filter paper have a large pore size which is not efficient for the filtration of colloid so, to reduce the size of pores collodion solution (cellulose nitrate solution) is used.

FAQs on Colloids

Q1: What are Colloids?

Answer:

Colloids are types of heterogeneous mixtures where the size of the suspended particle is between 1 and 1000 nanometers. For example, milk, curd, mayonnaise, etc.

Q2: What are some examples of colloids?

Answer:

Milk, for, blood, gelatin, paint, shaving cream, mayonnaise, smoke, ink, soil, etc. are some examples of colloids.

Q3: What are the properties of colloids?

Answer:

Some of the properties of colloids include their stability, heterogeneous nature but the homogenous appearance, and small size of the particles.

Q4: What are the applications of colloids?

Answer:

There are many application of colloids in food, beauty products, medicin etc.

Q5: How are colloids formed?

Answer:

There are various methods by which we get the colloids as products, some of these methods include oxidation, reduction, peptization, mechanical dispersion, etc.