Words like "pure" are often printed on packets of honey, milk, ghee, and coconut oil. In everyday language, this suggests that the product is natural or free from added impurities. However, in scientific terms, these substances are not considered pure.
For example, milk is made up of several different components such as fats, proteins, lactose (a type of sugar), minerals, vitamins, and water. Since it contains more than one type of substance physically combined together, it is classified as a mixture. Similarly, honey, ghee, and coconut oil also consist of multiple components.
In science, the term "pure substance" has a specific meaning. A substance is said to be pure when it contains only one type of particle throughout and has a fixed composition and definite properties.
From this understanding, matter can be broadly classified based on its composition into two categories: pure substances and mixtures.
Classification of matter:
Classification of matter
Pure substance:
The substances which are made up of only one kind of particles are known as pure substances.
Example: Water (\(H_2O\)), oxygen (\(O_2\)), gold \(Au\), and sodium chloride (\(NaCl\))
Mixtures:
A mixture is a substance formed by the physical combination of two or more substances in any proportion, where each component retains its own properties.
Example: Air, sand, sea water, butter, mineral water, and sugar/salt solution
Characteristics of a mixture:
- A mixture is made up of two or more substances physically combined.
- The components of a mixture can be present in any ratio.
- Each component of a mixture retains its own properties.
- The components of a mixture can be separated by physical methods (like filtration, evaporation, etc.).
Mixtures are classified into two types,
| Homogeneous mixture | Heterogeneous mixture |
| All of the mixture's components are blended evenly. |
All of the mixture's components aren't evenly distributed.
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| There are no visible separate barriers. | There are noticeable separate lines. |
| There is just a single-phase solution. |
There are two or more phase in the solution.
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Example: Salt dissolved in water, alloy, air
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Example: Sand water, oil in water, chalk in water
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Types of mixtures
Solutions:
A solution is a mixture of two or more substances that appears to be uniform in appearance. A solution is a homogeneous mixture of two or more substances.
Components of a solution:
Let us use a salt solution to understand the two main components of a solution.
Solute - The solute is the substance present in a smaller amount and is the one that gets dissolved. In a salt solution, salt acts as the solute.
Solvent - The solvent is the substance present in a larger amount and is the medium in which the solute dissolves. In a salt solution, water acts as the solvent.
Types of solutions:
1. Solids in a liquid solution: Salt solution, sugar solution
Solute: Salt is the solute.
Solvent: Water is the solvent.
Salt solution
2. Gas in a liquid solution: Aerated drinks
Solute: Carbon dioxide (gas) is the solute.
Solvent: Water (liquid) is the solvent.
Soft drinks
3. Solids in a solid solution: Alloys
Alloys are homogeneous mixtures of two or more metals, a metal and a non-metal, that can't be separated into their components using physical methods. Brass, for example, is made up of about \(30\) \(\%\) zinc and \(70\) \(\%\) copper.
Objects made from Brass
4. Liquids in a liquid solution: Lemonade
Solute: Lemon extract is the solute.
Solvent: Water is the solvent.
Lemon extract in water
5. Gas in a gas solution: Natural gas, air
Oxygen \(21\)% and nitrogen \(78\)% are the two primary constituents present in air along with small amounts of other gases like argon and carbon dioxide.
Properties of solution:
i. A solution is a homogeneous mixture.
ii. It is not possible to see the particles of a solution through the naked eye because these particles are smaller than \(1\) nanometer (\(10^{−9}\) \(metre\)) in diameter.
iii. A solution is clear and transparent, allowing light to pass through without scattering. Therefore, the path of light is not visible.
Scattering effect
iv. A solution can pass completely through filter paper because the solute particles are much smaller than the pores of the filter paper. Hence, they cannot be separated by filtration.
v. The solute particles do not settle down on standing, making the solution stable.
vi. The solute can be separated from the solution by methods such as evaporation or crystallisation.
Suspensions:
You may have played with mud during your childhood. Have you ever wondered what happens when mud is added to water? Does it dissolve?
When mud is mixed with water, it does not dissolve. Instead, the particles remain undissolved and settle down after some time. Such a mixture is called a suspension.
A suspension is a heterogeneous mixture in which the particles do not dissolve and settle down entirely in the medium.
Example: Clay mixture with water, flour in water, and mixture of chalk and water.
Properties of suspension:
i. Suspension is a heterogeneous mixture.
ii. The particles are relatively large, usually greater than \(1000\) \(nm\) in diameter, and can be seen with the naked eye.
iii. Suspension particles scatter a beam of light passing through it and make its path visible.
Note: When the suspended particles settle down, the beam of light is not scattered.
iv. When left undisturbed, the particles settle down due to gravity. This process is called sedimentation, showing that suspensions are unstable.
v. The particles can be separated from the medium by filtration.
Colloids:
In everyday life, the products we use, such as mayonnaise, jelly, and butter are the colloidal solution.
A colloidal solution is a heterogeneous mixture. In the colloidal solution, the particles of a colloid uniformly spread throughout the solution.
A colloid is a type of mixture that has properties between those of a solution and a suspension. Colloids can be identified by the Tyndall effect, which is the scattering of light when it passes through a colloidal solution.
Example: Milk, hair cream, toothpaste, fog, cheese, butter and paint
Tyndall effect on colloids
Properties of colloidal solution:
i. Colloidal solution is a heterogeneous mixture.
ii. A colloidal solution contains finely divided particles whose size ranges between \(1\ nm\) and \(1000\ nm\).
iii. Colloidal particles can scatter a beam of light passing through it and make its path visible.
iv. A colloidal solution is quite stable so that it does not settle down when left undisturbed.
v. These particles are small enough to pass through filter paper, so they cannot be separated by filtration.
vi. The particles in a colloidal solution can be separated by the process of centrifugation.
Types of colloidal solutions:
Classification of colloids based on the physical state of the dispersed phase and dispersion medium.
a. Dispersed phase: The dispersed phase is described as a phase that is scattered or present in the form of colloidal particles.
b. Dispersed medium: The dispersed phase is the medium in which colloidal particles are distributed.
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S.No
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Name
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Dispersed phase
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Dispersed medium
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Example
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1.
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Solid sol
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Solid
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Solid
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Colored glass, Gems, Alloys.
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2.
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Sol
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Solid
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Liquid
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Paint, Fruit jellies, Dye, Ink, Egg white
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3.
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Aerosol
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Solid
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Gas
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Smoke
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4.
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Gel
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Liquid
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Solid
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Cheese, Butter.
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5.
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Emulsion
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Liquid
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Liquid
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Milk, Oil in water, Mayonnaise, Face cream.
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6.
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Aerosol
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Liquid
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Gas
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Fog, Mist, Clouds, Body sprays.
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7.
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Foam
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Gas
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Liquid
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Soap lather, Shaving cream, Coffee froth
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8.
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Solid foam
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Gas
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Solid
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Rubber, Sponge, Cake, Bread
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