Exploring the Wonders of Nature: A Guide to CBSE Class 9 Science - IS MATTER AROUND US PURE
The Central Board of Secondary Education (CBSE) offers a comprehensive curriculum for Class 9 Science students. Students can access CBSE-aligned notes, practice questions, and other study materials to help them prepare for their examinations. Additionally, students can refer to the National Council of Educational Research and Training (NCERT) textbooks for detailed information on various topics and concepts. With the right resources, students can excel in their studies and gain a better understanding of the matter around us.
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CHAPTER 2 IS MATTER AROUND US PURE?
Substance
A substance is a kind of matter that cannot be separated into other kind of matter by any physical process. A pure substance is made up of same kind of elements.
Types of pure substances
It can be classified as element or compounds.
Elements
An element is defined as a pure substance which made up of only one kind of atoms. Ex- oxygen (O2)
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Elements can be normally divided into metals, non-metals and metalloids.
Compound
A compound is a pure substance made up of two or more element chemical combined in a fixed proportion by mass.
Example - water (H2O), common salt (NaCl)
Mixture
A mixture is a material made up of two or more substances (element or compound) are simply mixed together in any proportion.
Examples: The air is a mixture of oxygen, nitrogen, argon, carbon dioxide and water vapor.
Types of Mixture: Mixture is of two types:
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Homogenous mixture
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Heterogeneous mixture
Homogenous Mixture
It has no visible boundaries of separation between the various constituents, so they are called homogenous mixtures.
Example: Sugar in water. It has a uniform composition throughout its mass.
Heterogeneous Mixture
These types of mixtures have visible boundaries of separation between the various constituents.
Example: Mixture of sugar and sand. It does not have a uniform composition throughout its mass.
Solution
A solution is a homogenous mixture of two or more substances.
Example - Nimboopani, soda water.
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A solution has a solvent and a solute as its components. The component of the solution that dissolves the other component in it is called the solvent. The component of the solution that is dissolved in the solvent is called the solute.
Properties of a solution
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A solution is a homogeneous mixture.
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The particles of a solution are smaller than 1 nm (10^-9 meter) in diameter. So, they cannot be seen by naked eyes.
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Because of very small particle size, they do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution.
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The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed, that is, a solution is stable.
CONCENTRATION OF A SOLUTION
The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution, or the amount of solute dissolved in a given mass or volume of solvent.
Suspension
A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the medium.
Example - paint, lime water, etc.
Properties of a Suspension
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Suspension is a heterogeneous mixture.
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The particles of a suspension can be seen by the naked eye.
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The particles of a suspension scatter a beam of light passing through it and make its path visible.
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The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable. They can be separated from the mixture by the process of filtration.
Colloidal solution
A colloidal solution or simply colloid is a type of solution in which the size of the particles lies in between those of a true solution and a suspension.
Example – chalk solution, soap solution, milk, blood, etc.
Properties of a colloid
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A colloid is a heterogeneous mixture.
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The size of particles of a colloid is too small to be individually seen by naked eyes.
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Colloids are big enough to scatter a beam of light passing through it and make its path visible.
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They do not settle down when left undisturbed, that is, a colloid is quite stable.
Tyndall effect
The Tyndall effect is the phenomenon in which the particles in a colloid scatter the beams of light that are directed at them.
Example - smoke or dust in a room, which makes visible a light beam entering a window.
Physical change
A process in which a substance changes its physical appearance but from there is no change its basic composition, is called a physical change.
Example- boiling, melting, freezing etc.
Chemical change
A process in which new substance are formed whose properties and composition are different from the original substance is called a chemical change.
Example- burning, cooking, rusting etc.
Alloys
Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition.
For example, brass is a mixture of approximately 30% zinc and 70% copper