Classification of Colloids - Types of Colloids, Definition, FAQs
Have you ever wondered how substances like milk, ink, or even fog form? Looking at them, it doesn't seem like they are a mixture of two substances - but they actually are. These are examples of colloids, where particles are dispersed within another substance but are not large enough to settle out or be filtered. Colloids are a type of mixture in which one substance (called the dispersed phase) is finely distributed throughout another substance (called the dispersion medium). Colloidal particles are intermediate in size—larger than molecules in a solution but smaller than particles in a suspension.
This Story also Contains
- What Is a Colloid?
- Dispersion Medium And Dispersed Phase
- Classification Of Colloids
- Types Of Colloids
- Multimolecular Colloids
- Macromolecular Colloids
- Associated Colloids
- Lyophilic Colloids
- Lyophobic Colloids
- Some Solved Examples
In this article, we will discuss the classification of colloids, the dispersion phase, and the dispersion medium, types of colloids, and some solved examples related to them. To know more about colloids, scroll down.
What Is a Colloid?
A colloid is a heterogeneous mixture in which minute particles of one component are scattered in a dispersion medium of another substance.
The tiny particles in this combination range in size from 1 to 1000 nanometres in diameter, but they remain suspended and do not settle to the bottom. They can be seen with an optical or electron microscope (smaller particles).
A dispersed phase and a dispersion medium make up colloids. They're divided into groups based on the features of the dispersed phase and the medium. Let us discover more about them right now.
The following is the IUPAC definition of colloid:
“A colloidal state is a condition of dispersion in which molecules or polymeric particles with at least one dimension between 1 nanometre and 1 micrometre are distributed in a medium.”
Dispersion Medium And Dispersed Phase
Definition of colloidal dispersion
A colloid is a mixture in which a fine-particle-containing substance (dispersed phase) is combined with another component (dispersion medium). The colloids' particles range in size from 1 to 1000 nm in diameter. Because the particles of the solution do not mix or settle down, the solution is called a colloidal dispersion. In the solution, they are disseminated.
Definition of dispersed phase
The dispersed phase refers to the compounds that are distributed in the solution, whereas the dispersion medium refers to the solution in which they are dispersed.
Depending on the state of dispersion and the medium of dispersion
The following classification of colloid systems can be used depending on the state of dispersed particles and the dispersion medium.
- When the Dispersion Medium Is Liquid Foams – When the dispersion medium is a liquid foam. Whipped cream, shaving cream, and other similar products are examples.
- When the dispersed phase is liquid, it is called an emulsion. Milk, mayonnaise, and other foods are examples.
- When the scattered phase is solid, it is called sol. Blood, pigmented ink, and other materials are examples.
- When there is a gaseous dispersion medium
- When the dispersed phase is liquid, it is referred to as a liquid aerosol. Fog, mist, hair sprays, and other similar products are examples.
- When the dispersed phase is solid, it is referred to as a solid aerosol. Smoke, ice clouds, and more examples come to mind
Colloids are classified
When the dispersed medium is a gas, it is referred to as solid foam. Styrofoam, pumice, and other materials are examples.
When the distributed media is liquid, it is called a gel. Agar, gelatin, and other similar substances are examples.
When the scattered medium is solid, it is called solid sol. Cranberry glass is one example.
Also Read:
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Classification Of Colloids
Colloids are classified based on the nature of the interaction between the dispersed phase and the dispersion medium.
Colloids that are hydrophilic: These are colloids that like to be in the water. The water attracts the colloidal particles. Reversible sols are another name for them. Agar, gelatin, pectin, and other similar substances are examples.
Hydrophobic colloids are the polar opposites of hydrophilic colloids. The water repels the colloid particles. Irreversible sols are another name for them. Gold sols, clay particles, and other materials are examples.
Based on the Dispersed Phase Particle Type
Colloidal solutions can be categorised into three categories based on how different chemicals creating colloidal solutions acquire particle sizes in this range.
Types Of Colloids
The classification of colloids is done based on the types of colloids. The following are the categories:
- Multimolecular colloids
- Macromolecular colloids
- Associated colloids
Multimolecular Colloids
A solution created by the aggregation of a high number of atoms or tiny molecules (with diameters less than 1 nm) in a dispersed medium. Van der Waal forces hold the dispersed particles together.
Example:
Sulphur sol, and gold sol.
Macromolecular Colloids
Molecules with extremely high molecular weights combine to form macromolecules, which are exceedingly large molecules. The resulting colloidal solutions are known as macromolecular colloids when such compounds are dispersed in a suitable dispersion medium. As a result, macromolecular colloids have a large molecular mass. Lyophilic colloids are often macromolecular in nature.
Natural macromolecules, including starch, proteins, gelatin, cellulose, nucleic acids, and others, as well as synthetic polymers like polyethylene, polypropylene, and synthetic rubber, create macromolecular colloids when dispersed in suitable solvents.
Associated Colloids
When present in low quantities, some compounds behave as strong electrolytes, yet when present in high concentrations, they behave as colloidal sols. Particles agglomerate and demonstrate colloidal behaviour at greater concentrations. Micelles are microscopic clumps of collected particles. Associated colloids are another name for them. Micelles are formed above a certain temperature, known as the Kraft temperature (Tk), as well as a certain concentration, known as the critical micelle concentration. By diluting the colloids, they can be converted. Soaps and synthetic detergents are a couple of examples of related colloids.
Classification of colloids based on the interaction medium
Colloids can also be classed according on how the dispersed phase interacts with the medium:
Hydrophilic colloids: Colloids that love or are attracted to water are known as hydrophilic. Reversible sols are another name for them.
Agar, gelatin, and pectin are some examples.
Hydrophobic Colloid: These are the polar opposite of hydrophobic and repel water. Irreversible sols are another name for these.
Gold sols with clay particles, for example.
Colloids are characterised as lyophilic or lyophobic depending on the nature of the interaction between the dispersion medium and the dispersed phase.
Lyophilic Colloids
A lyophilic colloid is one in which the dispersed phase has an affinity for the dispersion medium. The words lyo and philic, respectively, signify "liquid" and "loving." Even if the dispersed phase and the dispersion medium are separated, they can easily be reconstituted by simply mixing them together. Furthermore, because of their sturdy nature, they are difficult to coagulate. Intrinsic colloids are another name for them. Starch, rubber, protein, and other materials are examples.
Lyophobic Colloids
A lyophobic colloid is one in which the dispersed phase has little or no affinity for the dispersion medium. The words lyo and phobic, respectively, denote "liquid" and "fear." As a result, they despise liquids. Because the dispersed phase does not readily form a colloid with the dispersion medium, they are difficult to manufacture and necessitate the employment of special techniques. They are brittle and require stabilising substances to stay alive. Extrinsic colloids are another name for them. Sols of metals such as silver and gold, as well as sols of metallic hydroxides, are examples.
Some Solved Examples
Question.1 Which of the following is an example of a colloidal solution?
a) Salt solution
b) Air
c) Milk
d) Sand in water
Solution:
Milk is a colloidal solution where fat droplets are dispersed in water. The particles in milk are of colloidal size and do not settle out easily, making it a true colloid. Salt solution is a true solution, air is a mixture of gases (not colloidal), and sand in water is a suspension.
Hence, the correct answer is option (c)
Question.2 Which of the following is true for colloidal particles?
a) They are smaller than molecules.
b) They settle under the influence of gravity.
c) They are visible to the naked eye.
d) They cannot be separated by filtration.
Solution:
Colloidal particles are larger than molecules but smaller than particles in a suspension. They do not settle under gravity and cannot be separated by simple filtration, but they can be separated by methods like ultrafiltration.
Hence, the correct answer is option (d)
Question.3 What is the main characteristic that distinguishes a colloid from a solution?
a) Colloids are heterogeneous, while solutions are homogeneous.
b) Colloids have larger particles than solutions.
c) Colloids scatter light (Tyndall effect), while solutions do not.
d) All of the above
Solution:
Colloids are heterogeneous mixtures, while solutions are homogeneous. Colloids have larger particles that are small enough to remain suspended but large enough to scatter light, which is known as the Tyndall effect. Solutions have particles that are too small to scatter light effectively.
Hence, the correct answer is option (d)
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Frequently Asked Questions (FAQs)
Emulsification is the process of forming an emulsion by dispersing one liquid in another immiscible liquid. It's achieved by applying mechanical energy (e.g., shaking, blending) and often using emulsifiers, which are substances that stabilize the emulsion by reducing surface tension between the two liquids.
Creaming is a form of emulsion instability where dispersed droplets rise to the top of the continuous phase due to density differences. It's often seen in oil-in-water emulsions where oil droplets are less dense than water. While not a complete breakdown of the emulsion, creaming is a step towards phase separation and indicates reduced stability.
The Hofmeister series ranks ions based on their ability to salt out or salt in proteins and affects colloidal stability. Some ions (e.g., sulfate) tend to increase surface tension and promote protein precipitation (salting out), while others (e.g., iodide) tend to decrease surface tension and increase protein solubility (salting in). This series helps predict ion effects on colloidal stability in various systems.
Ostwald ripening is a phenomenon where smaller particles in a colloid dissolve and redeposit onto larger particles over time. This process is driven by the system's tendency to minimize surface energy. It can lead to the growth of larger particles at the expense of smaller ones, potentially destabilizing the colloidal system.
Amphiphilic molecules, having both hydrophilic and hydrophobic parts, play a crucial role in forming and stabilizing certain colloids, especially emulsions and foams. They can orient themselves at interfaces, reducing surface tension and preventing coalescence of dispersed particles or droplets. This property makes them effective emulsifiers and foaming agents.
Salting out is the process of reducing the solubility of a substance in a solution by adding an electrolyte. In colloidal systems, high concentrations of salt can neutralize the charges on colloidal particles, reducing their stability and causing them to aggregate and precipitate out of solution. This effect is used in protein purification and other industrial processes.
Multimolecular colloids are formed by the aggregation of many small molecules into larger colloidal particles (e.g., gold sol). Macromolecular colloids consist of large molecules that are themselves of colloidal size (e.g., protein solutions). The key difference is in the nature of the dispersed phase: aggregates vs. single large molecules.
The critical micelle concentration (CMC) is the concentration of surfactants above which they spontaneously form micelles (associative colloids) in solution. Below the CMC, surfactants exist as individual molecules. Above the CMC, any additional surfactant forms micelles rather than increasing the concentration of free molecules, significantly changing the solution's properties.
Hydrophilic colloids have an affinity for water and tend to be more stable in aqueous environments. They often form spontaneously and can be easily redispersed if dried. Hydrophobic colloids, on the other hand, repel water and are less stable in aqueous media. They typically require more energy to form and maintain, and may not easily redisperse once separated.
Colloidal gold refers to a sol where gold nanoparticles are dispersed in water. It's typically prepared by reducing a solution of gold chloride with a reducing agent like sodium citrate. The resulting gold nanoparticles are stabilized by the citrate ions, creating a stable red or purple colloidal solution widely used in research and medical applications.
