CBSE Class 9

On this page, you will find Is Matter Around Us Pure Class 9 Notes Science Chapter 2 Pdf free download. CBSE NCERT Class 9 Science Notes Chapter 2 Is Matter Around Us Pure will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Science Chapter 2 Notes Is Matter Around Us Pure

Is Matter Around Us Pure Class 9 Notes Understanding the Lesson

1. Pure substance: A pure substance is defined as a material which contains only one kind of atoms or molecules. In pure substance all the constituting particles have the same chemical nature. Thus, a pure substance con¬sists of a single type of particles.

2. Pure substances are always homogeneous.

• Element: A pure substance which is made up of only one kind of atom.
• Compound: A pure substance which is made up of only one kind of molecules.

3. Mixtures: It is a form of matter in which two or more elements or compounds combine physically in any proportion by weight.

4. Types of Mixtures

• Homogeneous mixture: A mixture which has same composition throughout. Solutions are homogeneous mixtures. For example, air, sea water, grass, vinegar, etc.
• Heterogeneous mixture: A mixture which has different compositions in different parts. For example, sand, mud, iron filings, sulphur, etc.

5. Characteristics of Mixture

• Mixture may be homogeneous and heterogeneous.
• Mixture does not have a fixed melting point.
• In a mixture, the different constituents combine physically in any proportion by mass.
• The constituents of a mixture do not loose their identical property.
• Usually, no energy change take place during the formation of a mixture.

6. Solution
It is a homogeneous mixture of two or more non-reacting substances.

7. Solvent is the substance in which a solute is dissolved.

8. On the basis of the size of particles, solutions can be classified as:

• True solution
• Colloidal solution
• Suspension

9. True Solution : A homogeneous system in which the particle size is less than 1 nm. For example, sugar solution.

10. Properties of True Solution

• A solution is a homogeneous mixture.
• The particles of a solution are smaller than 1 nm in diameter. So, they cannot be seen by the naked eye.
• 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.
• 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.

11. Concentration of solution
There are two methods for expressing the concentration of solution.
Saturated solution: A solution in which no more of solute can be dissolved at a given temperature is called a saturated solution.
(i) Mass by Mass percentage of a Solution =\(\frac{\text { Mass of solute }}{\text { Mass of solution }} \times 100\)

(ii) Mass by Volume percentage of a Solution \(=\frac{\text { Mass of solute }}{\text { Volume of solution }} \times 100\)

12. Unsaturated solution: A solution in which more of the solute can be dissolved at a given temperature is called an unsaturated solution.
Suspension

13. A suspension: is a heterogeneous mixture in which one substance having particle size greater than 100 nm in diameter is spread throughout another substance. For example, muddy water, dust storm, aluminium paint, etc.

14. Properties of Suspension

• A suspension is a heterogeneous mixture.
• The particles of a suspension do not pass through a filter paper. Hence, it is possible to separate them by ordinary filtration.
• The particles of a suspension settle down when a suspension is left undisturbed. Thus, a suspension is unstable.
• The particles of suspension can be seen with naked eyes or with the help of a simple microscope.
• The size of particle in a suspension is greater than 100 nm in diameter.
• A suspension is not transparent to light.

15. Colloidal solutions
A solution in which the size of particles lies in between those of true solutions and suspensions are called colloidal solutions or colloids.
Colloidal solution is heterogeneous in nature and consists of two phases:

• Dispersed phase: It is the component present in small proportion and consists of particles of colloidal dimensions (1 nm to 100 nm).
• Dispersion medium: The solvent like medium in which colloidal particles are dispersed is called dispersion medium.

16. Properties of Colloidal Solutions

(i) Heterogeneous Nature: A colloidal solution is heterogeneous in nature. It consists of two phases— dispersed phase and dispersion medium.

(ii) Filtrability: The size of the colloidal particles is less than the pores of a filter paper,, and, therefore, they easily pass through a filter paper. Colloidal particles, however, cannot pass through the parchment paper or an animal membrane or ultra-filter.

(iii) Tyndall Effect: When a strong beam of light is passed through a colloidal solution placed in a dark place, the path of the beam gets illuminated by a bluish light. This phenomenon is called Tyndall effect. The phenomenon is due to scattering of light by the colloidal particles. The same phenomenon is noticed when a beam of sunlight enters a dark room through a small slit, due to scattering of light by dust particles in the air.

(iv) Visibility: Colloidal particles are too small to be seen by the naked eye. They, however, scatter light and become visible when viewed through an ultramicroscope.

(v) Brownian Movement: When colloidal particles are seen under an ultramicroscope, the particles are found to be in constant motion in zig-zag path in all possible directions. This zig-zag motion of colloidal particles is called Brownian movement. The movement of the particles is due to the collisions with the molecules of the dispersion medium.

(vi) Diffusion: Colloidal particles diffuse from a region of higher concentration to that of lower concentration. However, because of their bigger sizes colloidal particles move slowly and hence diffuse at a slower rate.

(vii) Sedimentation or Settling: Under the influence of gravity, the solute particles tend to settle down very slowly. This rate of settling down or sedimentation can be accelerated by the use of high speed centrifuge called ultracentrifuge.

17. Common methods for the separation mixtures are:

(a) Filtration: Filtration is the process of separating solids that are suspended in liquids by pouring the mixture into a filter funnel. As the liquid passes through the filter, the solid particles remain behind on the filter.

(b) Distillation: Distillation is the process of heating a liquid to form vapour and then cooling the vapour to get back the liquid. This is a method by which a mixture containing volatile substances can be separated into its components.

(c) Sublimation: This is the process of conversion of a solid directly into vapour on heating. Substances showing this property are called sublimate, e.g., iodine, naphthalene, camphor. This method is used to separate a sublimate from non-sublimate substances.

(d) Crystallisation: It is the process of separating solids having different solubilities in a particular solvent.

(e) Magnetic separation: This process is based upon the fact that a magnet attracts magnetic components from a mixture of magnetic and non-magnetic substances. The non-magnetic substance remains unaffected. Thus, it can be used to separate magnetic components from non-magnetic components.

(f) Atmolysis: This method is based upon rates of diffusion of gases and used for their separation from a gaseous mixture.

18. Physical Change: A temporary change which includes change in the shape, size, physical states and appearance of a substance,but not its chemical composition is known as physical change. Physical change is temporary and reversible. Chemical composition of the substance remains the same.
Examples:

• Heating of sulphur
• Sublimation of camphor
• Drying of wet clothes
• Breaking of glass

19. Chemical Change: A permanent change in which the chemical substance loses its own characteristics and composition and gives one or more new substances is called a chemical change. Chemical change is generally permanent and irreversible. Chemical change gives one or more new substances as products.
Examples

• Rusting of iron
• Digestion of food
• Burning of wood
• Ripening of fruit

20. Types of Pure Substances

1. Element: An element is defined as the simplest form or the basic form of a pure substance which can neither be broken into nor built up from simpler substances by any physical or chemical changes.

Properties of metals

• They have a lustre (shine).
• They have silvery-grey or golden-yellow colour.
• They conduct heat and electricity.
• They are ductile (can be drawn into wires).
• They are malleable (can be hammered into thin sheets).
• They are sonorous (make a ringing sound when hit).
  Examples of metals: Gold, silver, copper, iron, etc.

Properties of non-metals:

• They are poor conductors of heat and electricity.
• They are not lustrous, sonorous or malleable.
• They display a variety of colours.
  Examples of non-metals: Hydrogen, oxygen, iodine, bromine, chlorine, etc.
  Metalloids: Elements having certain properties of metals and non-metals are called metalloids.
  Examples: Arsenic, germanium, antimony and bismuth.

2. Compound: A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion. For example: Water is compound of hydrogen and oxygen elements and these elements are present in water in the ratio of
1 : 8 by mass.
Characteristics of compound:

• In a compound constituents are presents in definite proportion by mass.
• The properties of the compound are different from the properties of the constituents (elements) that make up the compound.
• The constituents of a compound cannot be separated by simple physical processes.
• A compound has a fixed melting point and boiling point.
• A compound is always homogeneous in nature.

Difference between mixture and compound

Class 9 Science Chapter 2 Notes Important Terms

1. Matter is defined as anything that has weight and occupies space.

2. Intermolecular force is the force of attraction between the consituent particles of matter.

3. Alloys are mixtures of two or more metals or a metal and a non-metal and cannot be separated into their components by physical methods.

4. Solution is a homogeneous mixture of two or more substances. The major component of a solution is called the solvent, and the minor, the solute.

5. Colloids are heterogeneous mixtures in which the particle size is too small to be seen with the naked eyes, but is big enough to scatter light.

On this page, you will find Matter in Our Surroundings Class 9 Notes Science Chapter 1 Pdf free download. CBSE NCERT Class 9 Science Notes Chapter 1 Matter in Our Surroundings will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Science Chapter 1 Notes Matter in Our Surroundings

Matter in Our Surroundings Class 9 Notes Understanding the Lesson

1. Matter is everything around you. Everything in this universe is made up of material which in scientific term is called matter.

2. Matter can be defined as anything that occupies space possesses mass, offers resistance and can be felt by one or more of our senses.

3. Examples: Water, air, plant, animal, stones, clouds, etc.
Matter is classified on the basis of their physical and chemical nature.

• Physical classification: On the basis of physical properties, matter has been classified as solid, liquid and gas.
• Chemical classification: On the basis of chemical composition, matter has been classified as element, compound and mixture.

4. Properties of Matter

• Matter is made up of small particles.
• Particles of matter have space between them.
• Particles of matter are continuously moving.
• Particles of matter attract each other because of force of attraction.

5. States of Matter
This classification is done on the basis of arrangement among particles, energy of particles and the distance between the particles.
(i) Solids:

• They have fixed shape and definite volume.
• They have small interparticle distances.
• They are incompressible.
• They are rigid.
• They have high density and do not diffuse.
• They have strong intermolecular forces of attraction.
• Their constituent particles are very closely packed.
• Their kinetic energy is very less.
  Examples: Sugar, salt, etc.

(ii) Liquids:

• They do not have fixed shape but have fixed volume.
• Their interparticle distances are larger than solids.
• They are almost incompressible.
• They have low density than solids.
• Their interparticle forces of attraction are weaker than solids.
• Their constituent particles are less closely packed.
• They assume the shape of the portion of the container they occupy.
• They can flow and thus can be called fluids.
• The kinetic energy of particles is more than that of solids.
• Examples: Milk, water, etc.

(iii) Gases:

• They have neither fixed shape nor fixed volume.
• Their interparticle distances are largest among the three states of matter.
• They have high compressibility.
• They have least density and diffuse.
• Their interparticle forces of attraction are weakest.
• Their constituent particles are free to move about.
• They can expand to occupy larger volume.
• They are also called vapour.
• The particles of gases have maximum kinetic energy.
• Examples: H₂, N₂, CO₂ etc.

6. Interchange of States of Matter

• Matter can be changed from one state to another state.
• Most of the metals, which are solid change into liquid on heating and then into vapour on further heating.
• The change of state of matter depends on:
  (i) Temperature
  (ii) Pressure

7. Effect of Change of Temperature

8. The temperature effect on heating a solid varies depending on the nature of the solid and the conditions required for bringing the change.

9. Generally on heating, temperature of substances increases. But during state transformation, temperature remains same.

10. On heating: The kinetic energy of particles increases which overcomes the force of attraction between the particles thereby solid melts and is converted to a liquid.

11. Melting point: It is the temperature at which a solid changes to a liquid at atomospheric pressure.

12. Different substances have different melting points.

13. Higher the melting point means large forces of attraction between the particles.

14. Melting point of ice is 273.16 K.

15. The process of melting is also known as fusion.

16. Melting point is characteristic propertyof a substance.

17. Latent heat: The hidden heat which breaks the force of attraction between the molecule is called latent heat.

18. It is the heat supplied to a substance during the change of its state.

19. It is the heat energy hidden in the bulk of matter.

20. Latent heat of fusion: Amount of heat energy required to convert 1 kg of a solid into a liquid at atmospheric pressure at its melting point is known as latent heat of fusion of a substance.

21. A solid having stronger interparticle forces has greater latent heat of fusion.

22. Latent heat of fusion of water is 333.7 kJ/kg.

23. Boiling point: The temperature at which a liquid starts boiling at atmospheric pressure is known as its boiling point.

24. A liquid having weaker interparticle forces has lower boiling point and is more volatile.

25. Latent heat of vapourisation: The amount of heat energy required to convert 1 kg of a liquid into a gas at atmospheric pressure at its boiling point is known as latent heat of vapourisation of the substance.

26. Latent heat of vapourisation of water is 2259 kJ/kg. Thus 1 kg of water in the form of steam at 373 K has 2259 kJ more energy than 1 kg of water at 373 K.

27. Condensation: The change of state from gas to liquid is called condensation.

28. The condensation process is reverse of vapourisation.

29. Freezing: The change of state from liquid to solid is called freezing.

30. Freezing is the reverse of melting or fusion.

31. Sublimation: Sublimation involves direct conversion of a solid into the gaseous state on heating and vice-versa.

32. Dry ice sublimes at -78 °C (195 K).

33. Camphor, ammonium chloride, iodine and naphthalene are some substances which undergo sublimation.

34. Effect of Change of Pressure

In the gaseous state, the interparticle spaces are very large and attractive forces between the particles are negligible. Because of large interparticle space, gases are highly compressible. When pressure is applied on a gas, enclosed in a cylinder, its molecules move closer and the gas undergoes appreciable compression. As the molecules move closer, the attractive forces between the molecules increase. At a sufficiently high pressure, the gas changes into liquid.

(i) Solid CO₂ is stored under high pressure. At a pressure of 1 atmosphere, solid CO₂ changes directly into gas without passing through the liquid state. Solid CO₂ is known as dry ice. Thus, we can conclude that we can liquefy gas by applying pressure and reducing temperature.

(ii) Change in volume from gaseous state to liquid state is very large whereas change in volume from liquid state to solid state is very small (negligible). This is due to the reason that in liquid the interparticle spaces are very small in a liquid.

(iii) Atmospheric pressure: The pressure exerted by the atmosphere or air is called atmospheric pressure. It decreases with increase in height.

(iv) Atmosphere (atm) is a unit of pressure.

(v) The SI unit of pressure is pascal (pa).
1 atm = 1.01 x 10⁵pa
1 bar = 1 x 10⁵ pa 1
bar = 1.01 atm.

(vi) Evaporation: The phenomenon of change of a liquid into vapour at any temperature below its boiling point is called evaporation.

(vii) Particles of matter possess kinetic energy. At a particular temperature, in a sample of liquid all the particles do not have same kinetic energy. There is a small fraction of molecule which has enough kinetic energy to overcome the attractive forces of other particles. If such a particle happens to come near the surface, it escapes into vapour state and evaporation takes place.

35. Factors Affecting the Rate of evaporation

(i) Surface area: Evaporation is a surface phenomenon, i.e., only the particles on the surface of the liquid gets converted into vapour. Thus, greater is the surface area, more is the rate of evaporation. For example, clothes dry faster when they are well spread out.

(ii) Increase in temperature: The rate of evaporation increases with increase in temperature. At higher temperature greater number of particles have enough kinetic energy to escape into the vapour state. For example, clothes dry faster in summer than in winter.

(iii) Decrease in humidity: The amount of water vapour present in air is referred to as humidity. The air cannot hold more than a definite amount of water vapour at a given temperature. If the humidity is more, the rate of evaporation decreases. For example, clothes do not dry easily during rainy season because the rate of evaporation is less due to high moisture content in the air.

(iv) Increase in the speed of the wind: With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding. For example, wet clothes dry faster on a windy day.

(v) Nature of liquid: Different liquids have different rates of evaporation. A liquid having weaker interparticle attractive forces evaporates at a faster rate because less energy is required to overcome the attractive forces. For example, acetone evaporates faster than water.

(vi) Evaporation causes cooling: Only the liquid particles having high kinetic energy leave the surface of the liquid and get converted into vapour. As a result, the average kinetic energy of the remaining particles of the liquid decreases and hence the temperature falls. Thus, evaporation causes cooling.

Class 9 Science Chapter 1 Notes Important Terms

Melting Point: It is the temperature at which a solid changes into liquid at atmospheric pressure.

Freezing point: The temperature at which a liquid freezes to become a solid at atmospheric pressure is called the freezing point.

Boiling point: The temperature at which a liquid starts boiling at atmospheric pressure is called its boiling point.

Latent heat of vapourisation: The amount of heat energy that is required to change 1 kg of liquid into vapour at atmospheric pressure at its boiling point is called latent heat of vapourisation.

Condensation: The process of changing a gas (or vapour) to a liquid by cooling is called condensation. Sublimation: Sublimation involves direct conversion of a solid into the gaseous state on heating and vice-versa.

Latent heat: The hidden heat which breaks the force of attraction between the molecules is known as latent heat.

Latent heat of fusion: The heat of energy required to convert 1 kg of a solid into liquid at atmospheric pressure, as its melting point, is known as latent heat of fusion.

Boiling: Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.

Evaporation: Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the force of attraction present in the liquid and change into vapour state.

On this page, you will find Probability Class 9 Notes Maths Chapter 15 Pdf free download. CBSE NCERT Class 9 Maths Notes Chapter 15 Probability will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Maths Chapter 15 Notes Probability

Probability Class 9 Notes Understanding the Lesson

1. Experiment: A procedure which produces some well-defined possible outcomes.

2. Random experiment: An experiment which when performed produces one of the several possible outcomes called a random experiment.

3. Trial: When we perform an experiment it is called a trial of the experiment.

4. Event: The set of outcomes of an experiment to which probability is assigned.

5. The empirical (or experimental) probability P(E) of an event E is given by
\(\mathrm{P}(\mathrm{E})=\frac{\text { Number of trials in which } \mathrm{E} \text { has happened }}{\text { Total number of trials }}\)
So, Probability of not happening an event \(\mathrm{P}(\overline{\mathrm{E}})\)= 1 – P(E)

6. The probability of an event lies between 0 and 1 (0 and 1 are included).

7. Impossible event: An event which never happens.

8. Certain event : An event which definitely happens.

On this page, you will find Statistics Class 9 Notes Maths Chapter 14 Pdf free download. CBSE NCERT Class 9 Maths Notes Chapter 14 Statistics will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Maths Chapter 14 Notes Statistics

Statistics Class 9 Notes Understanding the Lesson

There are two types of data:

• Primary
• Secondary.

We can represent the data by:

• Ungrouped and
• Grouped frequency distribution.

Data can also be represented by:

• Bar graph
• Histogram
• Frequency polygons.

Class mark of grouped data
\(=\frac{\text { lower limit }+\text { upper limit }}{2}\)

Measure of central tendencies are mean, median and mode.

Mean:

where, Σf_ix_i = Sum of all observations
Σf_i = Total frequency.

Median: Arrange the observations in ascending or descending order,

(i) If numbers of observations (x) are odd, then median \(\left(\frac{n+1}{2}\right)^{t h}\) terms

(ii) If number of observations (x) are even, then median \(\frac{n^{t h}}{2} \text { and }\left(\frac{n}{2}+1\right)^{t h}\)

Mode: The observation whose frequency is highest.

Relationship between mean, median and mode:
Mode = 3 Median – 2 Mean.

Graphical Representation of Data

• Bar graphs: A bar graph is a pictorial representation of the numerical data by a number of bars (rectangles) of uniform width erected horizontally or vertically with equal space between them. Each rectangle or bar represents only one value of the numerical data and the height or length of bar indicates the corresponding value of the numerical data.
• Histogram: A histogram or frequency histogram is a representation of a frequency distribution in the form of rectangles such that there is no gap between any two successive rectangles.
• Frequency polygon: It is another method of representing frequency distribution graphically.

On this page, you will find Constructions Class 9 Notes Maths Chapter 12 Pdf free download. CBSE NCERT Class 9 Maths Notes Chapter 12 Constructions will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Maths Chapter 12 Notes Constructions

Constructions Class 9 Notes Understanding the Lesson

• Geometrical construction means using only a ruler and a pair of compasses as geometrical instruments.
• Protractor may be used for drawing non-standard angles.

Construction of bisector of a line segment using compass

• Draw a line segment, say AB.
• With both the end points (A and B) of line segment as centre and taking radius of more than half of the measure of line segment, draw the arcs on both sides, which cut at two points on opposite side, say P and Q.
  
• Join these two points.
  This line (PQ) is the required bisector.

Construction of the bisector of a given angle (say ∠ABC)

• With A as centre and a small radius draw an arc, cutting AB at P and AC at Q.
• With P as centre and the same radius as above, draw an arc.
• With Q as centre and with same radius, draw another arc, cutting the previous arc at D.
  
• Join AD.

AD is the required bisector of ∠BCA.

• Construction of some Angies and Triangles ;
• Constructions of some standard angles such as 30°, 45°, 60°, 75°, 90°, 120° etc. are possible using a
  ruler and a pair of compasses. :
• Construction of a triangle is possible, when its base, a base angle and the sum of other two sides are given.
• Construction of a triangle is possible, when its base, a base angle and the difference of other two sides are given.
• Construction of a triangle is possible when its perimeter