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CBSE Class 9 Science, Is Matter Around Us Pure: Chapter notes (Part-I)

May 4, 2017 09:33 IST

    class 9 science chapter notesThis article brings you the CBSE Class 9 Science notes on chapter 2 ‘Is Matter Around Us Pure’ (Part-I) . These chapter notes are prepared by the subject experts and cover every important topic from the chapter. In between these notes you can try the questions asked from the discussed set of topics. These questions will help you to track your preparation level and get a hold on the subject.

    Main topics covered in this part of CBSE Class 9 Science,  Matter in Our Surroundings: Chapter Notes, are:

    • Matter and its Types
    • Elements
    • Compounds
    • Metals, Non-metals and Metalloids
    • Mixture and its Types
    • Solution and its Types
    • Solubility
    • Factors Affecting the Solubility
    • Concentration of Solution

    Key notes for Chapter- Is Matter Around Us Pure, are:

    Matter
    Anything which has mass and occupies space is called matter. It may be solid, liquid or gas.
    Types of Matter

    It is of two types :
    1. Pure Substance
    2. Impure substance

    types of matter


    1. Pure Substance:
    It  may be defined as a material which contains only one kind of atoms or molecules.
    Pure substances are again of two types:

    (a) Elements (b) Compounds

    (a) Elements:

    • Pure substances which are made up of only one kind of atoms are known as elements.
    • They cannot be split up into two or more simpler substances by any of the usual chemical methods.
    • For example: Iron, gold, silver, carbon, oxygen, nitrogen and sodium etc.

    CBSE Class 9 Science, Is Matter Around Us Pure: Important Topics and Questions

    Elements are further grouped into the following three categories:

    (i) Metals, for example: Iron, copper, gold, sodium, silver, mercury, etc.

    (ii) Non – metals, for example: Carbon, oxygen, sulphur, nitrogen, oxygen, hydrogen, etc.

    (iii) Metalloids : Boron, silicon, germanium, etc.

    Properties of Metals:

    • These are lustrous (shine).
    • They conduct heat and electricity.
    • All metals are malleable and ductile.
    • They are sonorous.
    •  All metals are hard except sodium and potassium.
    • All metals are solids at room temperature except mercury which is a liquid.

    Properties of Non-metals:

    • These are dull in appearance.
    • They are poor conductors of heat and electricity except diamond which is a good conductor of heat and graphite which is a good conductor of electricity.
    • They are neither malleable nor ductile.
    • They are generally soft except diamond which is the hardest natural substance known.
    • They may be solids, liquids or gases at room temperature.

    Metalloids: The elements that have properties intermediate between those of metals and non-metals, are called metalloids.

    (b) Compounds:

    • It is a form of matter formed by combining two or more elements in a definite ratio by mass.
    • It Can be decomposed into its constituent elements by suitable chemical methods
    • For example: Water (H2O), oxygen (O2), Nitrogen dioxide (NO2), etc.

    2. Impure Substance:  It  may be defined as a material which contains only one kind of atoms or molecules.

    It is also named as mixture.

    Mixtures:
    A mixture is a material which contains two or more different kinds of particles (atoms or molecules) which do not react chemically but are physically mixed together in any proportion.

    Types of mixture

    It is of two types:
    (a) Homogeneous mixture       (b) Heterogeneous mixture

    S. No.

    Homogeneous mixture

    Heterogeneous mixture

    1.

    All the components of the mixture are uniformly mixed.

    All the components of the mixture are not thoroughly mixed.

    2.

    No separation boundaries are visible.

    Separation boundaries are visible.

    3.

    It consists of a single phase.

    It consists of two or more phases.

    4.

     Example: Sugar dissolved in water

     Example: Air, sand and common salt.

    Difference between mixtures and compounds:

    S. No.

    Mixtures

    Compounds

    1.

    Various elements just mix together to form a mixture and no new compound is formed.

    Elements react to form new compounds.

    2.

    A mixture has a variable composition.

    The compound has a fixed composition.

    3.

    A mixture shows the properties of its constituents.

    Properties of a compound are  totally different from those of its constituents.

    4.

    They do not have a fixed melting point, boiling point, etc.

    They have a fixed melting point, boiling point, etc.

    5.

    The constituents can be seperated easily by physical methods

    The constituents can be separated only by chemical processes.

    Try the following questions:

    Q1. Is air around us a compound or a mixture?
    Q2. Water is a compound. Justify.
    Q3. Differentiate between homogeneous and heterogeneous mixtures.
    Q4. Give reasons for the following:

    (a) Copper is used for making electric wires.

    (b) Graphite is used for making electrode in a dry cell.

    Q5. List any four characteristics by which compounds can be differentiated from mixtures.

    Solution:
    A solution is a homogeneous mixture of two or more substances. For example: Lemon water, sugar solution, soda water, etc.

    Components of Solution:
    (1) Solvent:
    The component of the solution that dissolves the other component in it and is usually present in larger amount, such component of solution is called the solvent.
    For example: Water, alcohol etc.

    (2) Solute: The component of the solution that is dissolved in the solvent and is usually present in lesser quantity, such component is called the solute.For example: Salt, sugar, iodine etc.

    Properties of solutions:
    (i) It is a homogeneous mixture.
    (ii) Particle size in a solution is less than 1 nm in diameter.

    (iii) Particles of a solution cannot be seen even with a microscope.
    (iv) A true solution does not scatter the light.
    (v) Solution is stable.
    (vi) The solute particles cannot be separated from the mixture by the process of filtration.

    Types of solutions:

    Various types of solutions are:
    (i) Solid in a solid solution: Alloys.

    (ii) Solid in a liquid solution: Sugar solution, salt solution.
    (iii) Liquid sin a liquid solution: Lemon water, vinegar (acetic acid in water)
    (iv) Gas in a gas solution: Air.

    (v) Gas in a liquid solution: Soda water.

    Solubility:

    The maximum amount of the solute which can be dissolved in 100 grams of a solvent at a particular temperature is known as its solubility in that particular solvent.

    Conditions affecting solubility:
    (i) Temperature: Solubility of solids in liquids increases with the increase in temperature, whereas solubility of gases in liquids decreases on increasing the temperature.

    (ii) Pressure: Solubility of gases in liquids increases on increasing thepressure, whereas the solubility of solids in liquids remains unaffected by the change in pressure.

    Concentration of a Solution

    It is defined as the mass of the solute in grams present in 100 grams of the solution.

    Mathematical expression for concentration of solution:

    concentration of solid in liquid, solid in solidsolution

    In case of liquid solute in liquid solvent concentration can be expressed as:

    concentration of liquid in liquid olution

    Saturated Solution

    A solution in which no more quantity of solute can be dissolved at a particular temperature, is called saturated solution.

    Unsaturated Solution

    A solution in which more quantity of solute can be dissolved without raising its temperature, is called unsaturated solution.

    Try the following questions:

    Q1. What would it mean by saying a 15% of alcohol solution?

    Q2. Calculate the concentration of a solution containing 2.5g of salt dissolved in 50g of water.

    Q3. Name the different types of solutions along with an example for each.

    Q4. Define (a) Solute (b) Solvent.

    CBSE Class 9 Science Syllabus 2017-2018

    DISCLAIMER: JPL and its affiliates shall have no liability for any views, thoughts and comments expressed on this article.

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