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Colloids can be called dispersion of smaller particles, capable of being evenly distributed throughout the solution. A colloid is basically a mixture wherein one substance of dispersed insoluble particles is suspended throughout another substance. Aerosols, powders and pigments are examples of colloids. The importance of colloids touches almost every aspect of life, starting from biology, daily life to the environment we live in. It is mandatory for the particles to be within the range of 1 nanometer to 1 micrometre. Colloidal suspension refers to the overall mixture. A colloid has a dispersed phase and a continuous phase unlike a solution, in which solute and solvent constitute only one phase. Let us take important notes regarding colloidal solutions, their types, examples and their importance in our lives.
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Keyterms: Colloids, Dispersion, Solution, Insoluble particles, Aerosols, Powders, Pigments, Mixture, micrometre, nanometer
What is a Colloid?
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Italian chemist Francesco Selmi was responsible for first introducing the idea of colloids and colloidal suspension in 1845. Later this theory was modified and investigated by other scientists. A colloid has been defined as a mixture of a substance consisting of dispersible particles which are microscopically insoluble and has the ability to be distributed throughout another solution. According to some theories, these particles must be dispersed in a liquid, whereas according to other definitions, it demands to be dispersed in aerosols and gels.
Colloidal suspension denotes the overall mixture. There are two phases of a colloid named the dispersed phase, and the continuous phase. The dispersed or the scattering phase refers to the suspension of the particles whereas the continuous phase refers to the medium of suspension. The linear dimensions in the phase of the dispersion of particles must be between 1 nanometer to 1 micrometre.
By observation, it has been found that colloids may take the form of being opaque, which is neither transparent nor translucent. In some cases, they may possess some colour. The Tyndall effect is responsible for the colloids being translucent. This happens because of the light being scattered by the particles present in the colloid.
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| Related Articles | ||
|---|---|---|
| Classification of Colloids | Properties of Colloids | Simple Microscope |
| Total Internal Reflection | Refraction at Spherical Surfaces | Dispersion Through Prism |
Examples of Colloids
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In Biology
Colloids play a very crucial role in Biology for the division of cytoplasm and nucleus of individual cells. They are responsible for breaking them down into a type of liquid crystal. This colloidal phase separation is enhanced by macromolecular crowding. The formation of biomolecular condensates is thus effectively formed.
In Daily Life
If we look carefully, we can see the usage of different forms of colloids in our everyday life. They are present all around us. These are present in the form of a liquid and solid aerosol, foam, gels, emulsion, sols, and solid sols.
- We can find colloids present in the form of liquid aerosols in products like the perfumes we use to contain them. Disinfectants or mosquito repellents are also examples of liquid aerosols. The fog which occurs naturally, or smoke emitted from vehicles end up forming into a colloidal substance
- Dust particles present in the atmosphere are forms of solid aerosols. The dispersion medium is gas here, while the phase which is dispersed happens to be solid.
- We often use shaving cream, which takes the form of foam, again an example of a colloid. The whipped cream used in pastries and cakes is also counted.
- When both dispersed phase and medium are liquid, we call them emulsions. We find this every day around us like milk which occurs in nature naturally, body lotions or creams we use in our cosmetics, or the mayonnaise we use for sandwiches, are all examples of emulsions.
- Man-made paints are present in the form of sols while butter and other jelly products like jam which we use as spreads come under gels. Medicines, products made from cushion materials fall under the category of solid sols.
In Chemistry
Colloids can be evidently found in Chemistry as pigmented plastics, toothpaste, and silver iodide. Pigmented plastics are in the solid-state with the dispersion medium being solid as well. In the case of toothpaste and silver iodide, and au sols, all of these are forms of solid and the dispersion medium is a liquid. We use the term sol when colloidal solutions are subjected to high temperatures.
In Medicine
- Colloids are often used in the form of iso molars and possess the ability to cause allergies in the body. It has been clinically proven that they have limited exposure as compared to synthetic ones.
- They serve the role of extremely efficient volume expanders. They don't easily pass through capillary membranes because they hold particles with high molecular weight in them.
- In medicine, doctors often take the help of synthetic colloids when a patient is suffering from a haemorrhage. These are given according to special procedures for intravascular volume expansion.
Examples of Colloidal Solutions
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Colloidal solutions have unique characteristics. These are,
- Colloids can effectively attract or pull fluids into the bloodstream. This effect stays up for many days. Shampoo, milk, even liquid metal shoe polish are considered as examples of colloids
- Zero gravitational effects
- Thermal kinetic energy increases the mobility
- Doctors, while working prefer colloids more to crystalloids
Types of Colloidal Solutions
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Colloids are classified into different categories according to their dispersed phase and mediums.
| Dispersed phase | Dispersed medium | Type of colloidal solution | Example |
|---|---|---|---|
| Gas | Liquid | Foam | Whipped cream, shaving cream, soap suds |
| Liquid | Gas | Aerosol | Cloud, fog |
| Solid | Liquid | Sol | Sulphur sol |
| Solid | Solid | Solid sol | Coloured glasses |
| Liquid | Solid | Gel | Jam, butter, cheese, jelly |
| Liquid | Liquid | Emulsion | Naturally occurring milk, mayonnaise |
| Solid | Gas | Aerosol | Smoke |
When water acts as the dispersing medium, any colloid present there can be called hydrophobic or hydrophilic. The attractive force is very weak here, that is between the water and the surface of the colloidal particles.
In the case of precipitation of silver chloride, the end product is always a colloidal dispersion. This process of precipitation occurs quickly for ions. They gather and form crystals very fast. Later in the process, these ions start to come together with smaller particles remaining suspended in the liquid. Many soil particles lie on the ground. These particles are often carried by water during rain. These are deposited in water beds like rivers and lakes, in the form of hydrophobic colloids. In the end, process, when the water of the rivers comes in contact with the water of the sea, the sea has a high concentration of salts in itself which is why particles coagulate and end up forming silt.
Properties of Colloidal Solution
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Some of the main properties of the colloidal solutions are as follows:
Physical properties
- Heterogeneous nature: Colloidal solutions are heterogeneous in nature and are consist of two phases; a dispersion phase and a dispersion medium.
- Stable nature: Such solutions are quite stable as they are always in a state of motion and never settle down at the bottom of a container
- Filterability: Colloidal particles can easily be passed through ordinary filter papers.
Colligative properties
- Observed values of colligative properties like relative decrease vapour pressure, elevation in boiling point, depression in freezing point, osmotic pressure are smaller than expected due to the formation of associated molecules.
- The number of particles will be comparatively small for a given solution.
Mechanical properties
- Diffusion: The sol particles diffuse from higher concentration to lower concentration region. But due to the bigger size, they diffuse at a lesser speed.
- Sedimentation: Under the influence of gravity the colloidal particles settle down very slowly. This phenomenon is used in order to determine the molecular mass of the macromolecules.
Things to Remember
- Colloids are the dispersion of smaller particles that are capable of being finely distributed throughout another solution. The linear dimensions of the particles are to be present between i nanometer to 1 micrometre.
- Colloids are divided into many categories depending upon their dispersed phase and dispersed medium. These are aerosols, foam, gels, emulsions, solid sol, sol, solid foam, etc.
- Colloids play a vital role in medicine, everyday life, biology, our environment and chemistry as well. They have a huge contribution to almost every field of our life. They help in storing minerals and also are known as excellent thickening agents.
- The Tyndall effect is the scattering of light by particles present inside a colloid. It was introduced by John Tyndall.
- The theory matches the Rayleigh theory and explains why the blue light is much more distributed than the red light. The blue colour of the iris and visible rays of sunlight is a very commonly occurring phenomenon in nature.
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Sample Questions
Ques: What is the difference between lyophilic and lyophobic colloids? (3 marks)
Ans: Lyophilic colloids are those colloids that are solvent ling. For example, starch, protein, gum, etc. have a high affinity for the dispersion medium. On the other hand, lyophobic colloids are solvent hating colloids with almost zero affinity for the dispersion medium. Lyophilic colloids can be prepared easily by just shaking, mixing or heating up the substance with the dispersion medium. Special methods are necessary for the preparation of lyophobic colloids in addition to a stabilising agent.
Ques: What are colloids? (3 marks)
Ans: Colloids or colloidal dispersions are referred to as the dispersion of the particles. The dimensions of these particles must be within the range of 1 nanometer to 1 micrometre. The particles may be dispersed in liquid, gels, or aerosols. They are called colloidal dispersions because the particulate matter remains scattered without settling at the bottom. The theory about colloids was first introduced by an Italian chemist, Francesco Selmi.
Ques: Give examples of the Tyndall effect. (3 marks)
Ans: Blue coloured iris is an amazing example of the Tyndall effect. We see some people have blue eyes. It's not because there are some coloured particles present inside their eyes. When the eyes occur blue, it means the storm is translucent, hence pigments. White light falling incident on it is reflected and scattered due to reflection. Blue colour has a wavelength shorter than the rest of the colours which is why it is scattered more. This is the reason eyes appear blue, thereby explaining the Tyndall effect.
Ques: What are Lyophilic colloids? (2 marks)
Ans: A lyophilic colloid or lyophilic sols is a colloidal system, where the colloids are solvent attracting. These are highly solvated and much more stable as compared to lyophobic colloids. When dissolved, the dispersed particles have a layer of dispersion medium covering them. In order for coagulation to take place, a huge amount of electrolytes are required.
Ques: Give examples of colloids in daily life. (4 marks)
Ans: The examples of colloids used in daily life can be explained by the following,
- In the form of foam,
- Shaving cream which forms a lather
- Whipped cream used in cakes or pastries
- In the form of gel
- Butter is used as a spread on bread
- Jam or jelly type edible substances used as a spread
Ques: Why are colloids important? (2 marks)
Ans: Colloids are important because we require their assistance for purifying drinking water, tanning, medicine, etc. they are crucial for cleansing soap and detergent and are also responsible for the electrical precipitation of smoke. It is because of its attributes that colloids are used in photographic plates, rubber industry, colloidal graphite and artificial rain. It also acts as an effective disinfectant.
Ques: What are the types of colloids? (2 marks)
Ans: Sol is a colloidal suspension consisting of solid particles present inside a liquid. Emulsion refers to a type of colloid that takes place only between two liquids. The foam takes place when uncountable particles of gas are inside in a liquid or solid, whereas an aerosol is a colloid that possesses minute particles of liquid or solid dispersed in a gas.
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