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Colloid is a mixture of two substances, where particle of one substance are relatively larger than the average atoms but small enough to be invisible to the naked eyes and is dispersed uniformly in the second substance. Colloids or also known as colloidal dispersions, depict properties that lie between those of suspension and solution. The dispersed particle size varies between 1 to 1000 nanometres. Colloids form a big part of everyday life for example, milk, foam and smoke, all are colloids.
An electron microscope can be used to view these suspended particles very easily. The term “colloid” comes from the Greek words kolla, meaning “glue,” and eidos, meaning “like”.
Also Read: Difference between Light and Electron Microscope
| Table of Content |
Key Terms: Colloids, Suspensions, Solutions, Mixtures, Brownian Movement, Tyndall Effect, Surface Chemistry
What is Colloid?
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The three primary types of mixtures are suspension, solution and colloid. A colloid is a mixture that has dispersed particles larger than average molecules but still small to be seen by naked eyes. They remain evenly distributed throughout the solution. These are also known as colloidal dispersions because the particles remain dispersed and do not settle to the bottom of the container. In simple terms, colloid is a mixture where one substance is dipersed in another. The substance that is dispersed is known as being in the dispersed phase, while the substance in which it is dispersed is in the continuous phase or the dispersing medium.
Solution, Colloid and Suspension under Light
- A colloid with water as the dispersing medium can be classified as hydrophobic or hydrophilic.
- A hydrophobic colloid is one in which only weak attractive forces exist between the water and the surface of the colloidal particles.
- Hydrophilic colloids are water-loving colloids, i.e., the colloid particles are attracted toward water.
- Some colloids can be translucent because of the Tyndall effect while others may be opaque or have a slight color.
Types of Colloid
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Colloids can be classified based on three different criteria:
- Particles Size
- Interaction
- Dispersion Phase and Dispersion Medium
Particles Size
Colloids are divided into three sub-categories based on their particles size as: Multimolecular Colloids, Macromolecular Colloids and Associated Colloids.
| Multimolecular Colloids | Macromolecular Colloids | Associated Colloids |
|---|---|---|
| Dispersed phase forms an aggregate of a large number of atoms or small-sized molecules forming a species of suspended particles inside the dispersed medium to form a multimolecular colloid. | The size is comparatively bigger but remains within the size range required to form a colloidal solution. They are quite stable and match with the properties of a solution in different aspects. | Some electrolytes at high concentration behave like a colloidal system. The higher concentration of the electrolytes results in the physical union of smaller particles forming bigger particles. |
| Lyophilic in nature | Lyophobic in nature | Both lyophilic and lyophobic in nature |
| Medium molecular mass | High molecular mass | High molecular mass |
| Weak Van der waal force | High Van der waal force due to long chains | Van der waal force increase with increase in concentration |
Interaction
Based on interaction between the dispersed phase and the dispersing medium, colloids are divided into two types as Lyophilic and Lyophobic colloids. A brief differentiation between the two is given below:
| Lyophilic Colloids | Lyophobic Colloids |
|---|---|
| These are solvent loving colloids. | These are solvent hating colloids. |
| They are thermodynamically stable. | They are thermodynamically unstable. |
| Precipitation in lyophilic sol is a reversible process. | Precipitation in lyophobic sol is an irreversible process. |
| Strong attractive force between colloids and the liquid. | Weak attractive force between colloids and the liquid. |
| These colloids are highly viscous. | Viscosity is same as of the solvent. |
Dispersed Phase and Dispersion Medium
Based on the different dispersed phase and different dispersion mediums, colloids are divided into many sub-categories as explained below in the table.
| Dispersed Phase | Dispersion Medium | Colloidal System Name | Examples |
|---|---|---|---|
| Liquid | Gas | Liquid Aerosol | Mist, Fog |
| Solid | Gas | Aerosol | Dust, Smoke |
| Gas | Liquid | Foam | Whipped cream |
| Liquid | Liquid | Emulsion | Milk, Mayo |
| Solid | Liquid | Sol | Paints, Sewage |
| Gas | Solid | Solid Foam | Marshmallow, Rubber |
| Liquid | Solid | Solid Emulsion | Butter, Cheese |
| Solid | Solid | Solid Sol | Alloys, Gems |
Examples of Colloid
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The properties of colloidal dispersions and surface chemistry are closely linked together and thus provide a variety of examples in both everyday life and research areas. A few examples are as follows:
- The aerosol sprays that we either use as personal perfumatory products usually contain aerosol.
- Naturally occurring fog and clouds, the smog or the smoke and fog combination which creates a thick slowly moving colloidal material, are all liquid aerosols.
- Various types of cosmetic lotions we use on a daily basis are an example of emulsion.
- Ink and other products which are basically combination of sols made at a high temperature.
- Colloids play a very important role in medicinal department as well and are considered as very good intravascular volume expanders.
- Colloids help in pulling fluid into the bloodstream. Their effects last several days if the lining of the capillaries is found to be normal.
- Certain electrolytes, such as alum, can be used to precipitate colloidal pollutants present in water. The Al3+ ions neutralize the negatively charged colloidal particles of contaminants, which settle down and allow pure water to be decanted off.
- Latex is a colloidal solution containing negatively charged rubber particles used in the rubber industry.
Also Read:
Characteristics of Colloid Solution
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Most of the colloid solutions represent following characteristics:
- Thermal kinetic energy helps in the mobility of the particles.
- The inertial effect is absent from fluids.
- There are no or neglible gravitational effects.
- The interaction between solvent and dispersed particles depnds on the electromagnetic radiation.
- Day to day examples are milk which is considered to be the best example of colloid, the shampoo that we get to use, liquid hand wash and many more.
- They show Brownian movement as it arises because of the impact of the molecules of the dispersion medium with the colloidal particles.
- Colloids exhibit Tyndall effect in which the particles scatter the beams of light that are directed at them.
Previous Years’ Questions
- The colloidal solution in which both the dispersed phase and dispersion medium arc liquids called… [KCET 2009]
- The continuous phase contains the dispersed phase throughout… [VITEEE 2008]
- The ability of anion to bring about coagulation of a given colloid depends upon… [NEET 1997]
- The coagulation values in millimoles per litre of the electrolytes used for the coagulation of… [NEET 2016]
- The protecting power of lyophilic colloidal sol is expressed in terms of… [NEET 2012]
- Sulphur sol contains… [KCET 2016]
- The basic principle of Cottnell's precipitator is… [KCET 2008]
- The aerosol is a kind of colloid in which... [JEE Main 2019]
- The best coagulant for the precipitation of… [JKCET 2011]
- The charge on… [JKCET 2010]
Things to Remember
- A colloid is a mixture that has dispersed particles larger than average molecules but still small to be seen by naked eyes.
- Colloids remain evenly distributed throughout the solution.
- A colloid with water as the dispersing medium can be classified as hydrophobic or hydrophilic.
- Hydrophilic colloids are water-loving colloids, i.e., the colloid particles are attracted toward water.
- Colloids help in pulling fluid into the bloodstream. Their effects last several days if the lining of the capillaries is found to be normal.
Sample Questions
Ques: What are colloids? (2 Marks)
Ans: A colloid is a mixture that has dispersed particles as larger than average molecules but still small to be seen by naked eyes. These are also known as colloidal dispersions because the particles remain dispersed and do not settle to the bottom of the container. In simple terms, colloid is a mixture where one substance is dipersed in another.
Ques: Can a colloid particles aquire an electric charge? (2 Marks)
Ans: When two platinum electrodes are dipped in the colloidal solution and placed in a U-tube and the current is turned on, colloid particles migrate to the oppositely charged electrode when the circuit is closed, and when they reach that electrode, they are discharged. The particles agglomerate and settle down as soon as their charge is neutralized. In the case of real solutions, this movement of colloid particles in an electric field is known as electrophoresis
Ques: What is Tyndall Effect? (2 Marks)
Ans: The Tyndall effect is a simple method for assessing whether a mixture is colloidal or not. When light is shone through a true solution, it passes through it cleanly; however, when light is shone through a colloidal solution, the substance in the scattered phases scatters and can be seen because the light is reflected in all directions.
Ques: Give examples of macromolecular colloids. (1 Mark)
Ans: Some biomolecular such as enzymes or protein which are quite bigger in size when immersed in a suitable dispersion medium and their particle aggregate to form sols are examples of macromolecular colloids.
Ques: Mention some examples of colloids in medicinal field. (2 Marks)
Ans: Colloids are considered to be very good intravascular volume expanders. These are fluids with high molecular weight substances that do not pass through capillary membranes usually. The osmotic pressure of these materials exerted by Colloid is related to the size of the molecule. The smaller the molecule size, the higher the initial oncotic pressure, because the smaller molecules fit into a volume of fluid than larger molecules. Colloids used in the medicinal field are usually osmolar and have the potential to cause allergic reactions in the body, but clinically these appear to have limited exposure to these synthetic ones.
Ques: Define Brownian Movement. (2 Marks)
Ans: Brownian motion is the zig-zag motion of a particle as a result of collisions with surrounding gaseous molecules. Some of it examples are the motion of pollen grains on still water, movement of dust motes in a roomand diffusion of pollutants in the air.
Ques: Explain the cleansing action of soap. (1 Mark)
Ans: Soap solution is colloidal in nature. It removes the dirt particles either by adsorption or by emulsifying the greasy matter sticking to the cloth.
Ques: How are lyophilic and lyophobic sols are different? (2 Marks)
Ans: In lyophilic sols, there is a strong interaction between the dispersed phase and dispersion medium, highly stable and resistant to coagulation. Lyophobic sols are unstable weak unstable Van Der Waals forces of attraction between dispersed phase and dispersion medium due to these forces these are irreversible and ready to coagulate.
Ques: What are the four types of colloids? (1 Mark)
Ans: The four types of colloids are Emulsion, Sol, Aerosol and Foam.
Ques: Is blood a type of colloid? (1 Mark)
Ans: Blood is a colloidal suspension. It consists of lymphocytes, red blood cells, and white blood cells suspended in plasma.
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