CLASS-9-SCIENCE CH-2-IS MATTER ARROUND US PURE?
Pure Substance:
A pure substance is made up of only one type of particles.
Example – 1. Pure copper is made up of only copper atoms.
2. A pure gold coin is only made up of gold atoms.
3. Pure sugar consists of only C12H22O11 molecules etc.
Types of Pure Substances:
Pure substances can be classified into following ways.
(1)Element
(2)Compound
Element:
According to Antoine Laurent Lavoiser , a French chemist, an element is the basic form of pure matter which can not be broken down into still simpler substances by chemical reaction.
Classified of Element:
1. Metal
2. Non-Metal
3. Metalloid
Metals:
Such a sodium, potassium, iron, lead, copper, silver, zinc, Aluminium, gold, etc.
Characteristics of Metals:
(i) They are solid at room temperature. Mercury is the only metal which is liquid at room temperature.
(ii) They posses silvery-grey or golden yellow color.
(iii) They usually posses lustre (or shine). Silver is the best reflector of light.
(iv) They can be beaten by hammer into thin sheets, i.e., They are Malleable. For example: Aluminium foils are used in packaging of medicines, biscuits, etc.
(v) They can be drawn into thin wires, i.e., They are Ductile.
(vi) They making a ringing sound when hit, i.e., They are Sonorous. Therefore temple bells, strings of musical instruments are made of metals.
(vii) They are good conductors of heat and electricity. Silver is the best conductor of heat and electricity.
(viii)Their melting and boiling points are high. The melting point of tungsten is 3422º C. But sodium, potassium and gallium have low melting points.
(ix) Their densities are high.
(x) Metals have high tensile strength and are hard. But sodium and potassium have low tensile strength.
Non-Metals:
Such as hydrogen, carbon, oxygen, nitrogen, sulphur, phosphorus, chlorine, etc.
Characteristics of Non-Metals:
(i) They, generally, posses strength and have tower tensile compared to metals.
(ii) They posses a variety of colors. For example, sulphur is yellow; while bromine is brown in color.
(iii) They are either solid (e.g., sulphur, phosphorus and iodine) or liquid (e.g., bromine) or gaseous (e.g., hydrogen, nitrogen and oxygen) in state.
(iv) They are poor conductors of heat and electricity.
Note: Graphite (a form of carbon) is a good conductor of electricity. Therefore, it is used as an electrode in dry cell.
(v) They are neither malleable nor ductile.
(vi) They are neither lustrous nor sonorous. They are brittle.
Exceptions: Iodine and graphite are lustrous non-metal.
(vii) They are held together by comparatively weaker bonds, so their melting and boiling points are not high.
Metalloids:
Metalloids are elements exhibiting both metallic and non-metallic properties. For example, boron silicon, arsenic, germanium, etc.
Compounds:
A Compound is a substance composed of two or more elements in definite proportion by mass.
Characteristics of Compounds:
(i) In a compound two or more elements are combined together by chemical force.
(ii) A compound is always homogenous, i.e., particles are identical in composition and properties.
(iii) The proportion of different constituents (or elements)of a compound is always fixed by mass.
(iv) A Compound differs altogether in physical and chemical properties from the constituent elements of which the compound is formed.
(v) A compound cannot be separated into its constituents or elements by physical or mechanical means.
(vi) The formation of a compound from its constituents or elements is, usually, accompanied by either liberation or absorption of energy.
(vii) A compound possesses definite melting and boiling points.
Mixture:
Mixture contains more than one kind of pure substance.
Types of Mixture:
(i) Homogenous Mixture
(ii) Heterogenous Mixture
Homogenous Mixture:
Homogenous mixture is one which has uniform composition throughout the sample. For example, salt solution in water, tap water, ink brass, etc.
Heterogenous Mixture:
Heterogenous mixture is one which has non-uniform composition. For example, a suspension of chalk in water, sand in water, etc.
Characteristics of Mixture:
(a) All mixtures (except solutions) are heterogenous, the composition is not uniform throughout. Thus, composition of air which contains dust particles and pollutants is a heterogenous mixture. This is because dust particles/pollutants are different at different places.
(b) The components of mixture can be separated by a simple method like using magnet, decantation, filtration, distillation, sublimation, etc.
Solution:
A solution is a homogenous mixture of two or more substances.
Types of Solution:
(i) Solute
(ii) Solvent
Solute:
The substance that is dissolved or undergoes a change in its physical state is called a solute.
Solvent:
The substance that dissolves the other substance and does not undergoes a change in its physical state, is called a solvent.
Types of Solutions on the basis of Solute and Solvent:
(a) Solid in liquid solutions
(b) Liquid in solid solutions
(c) Gas in liquid solutions
(d) Solid in solid solutions
Properties of a Solution:
(a) It is a homogenous mixture (i.e., in a solution, there is homogeneity at the particle level).
(b) The particles of a solution cannot be seen by naked eyes, because the size of particles of a solution is smaller than 1nm (1nm=10-9).
(c) A solution does not scatter a beam of light passing through it. This is because the particle size is so small that it cannot scatter light. As a result, the path of light through a solution is not visible.
(d) A solution is stable because the solute particles cannot be separated easily and do not settle down, when left undisturbed.
(e) The process of filtration cannot separate the solute particles from a solution.
Types of Solutions on the basis of Nature of Solvent:
On the basis of nature of solvent, solutions are two types:
(a) Aqueous Solution
(b) Non-Aqueous Solution
Aqueous Solution:
Aqueous solution is the solution obtained by dissolving a solid in water. For example, Solution of common salt in water, Solution of sugar in water, etc.
Non-Aqueous Solution:
Non-Aqueous Solution is the solution obtained by dissolving a solid in liquid other than water like alcohol, benzene, acetone, carbon, disulphide, etc. For example, Tincture iodine(a solution of iodine in alcohol), solution of sulphur in carbon disulphide, etc.
Saturated Solution:
A solution in which no more solute can be dissolved at a given temperature is called saturated solution.
Unsaturated Solution:
A solution in which more solute can be dissolved at a given temperature, is called unsaturated solution.
Solubility:
The amount of solute that can be dissolved in 100 grams of solvent at a given temperature to give a saturated solution, is called the solubility of that solvent at that temperature.
Concentration of Solution:
Concentration of a solution is a measure of the amount of solute present in (a) a given amount (mass/volume) of solvent or (b) a given amount (mass/volume) of solution.
(a)Mass Percentage:
Mass Percentage = Mass of solute/Mass of solute *100
If W g of solute is dissolved in W g of solvent, then mass percentage of solute
∴ Mass Percentage = w/w + W*100
For example, if 100 g of solution contains 15g of solute, then w = 15g, w + W= 100 g.
∴ Mass Percentage of solute = 15g /100g*100 = 15%
Alternatively, if 15g of solute is dissolved in 85g of solvent, then :
w = 15g; W = 85g
or w + W = (15 + 85g = 100g).
∴ Mass percentage of solute = 15g/100g*100 = 15%
and mass percentage of solvent = 100 – 15 = 85%.
(b)Mass by Volume Percentage:
Mass by Volume Percentage = Mass of solute/Volume of solution*100
If “m” gram of a solute is present in V Litre of solution, then mass by Mass Volume Percentage of solute is given by:
Mass by Volume Percentage = m/V*100
For example, if a solution contains 20g solute in 120ml of solution, then m = 20g; V =120ml.
Mass by Volume Percentage of alcohol = 20/120*100 = 16.67%.
Suspensions:
Suspensions are Heterogenous mixtures.
When the size of solute particles in liquid is bigger than 10-6m then the mixture is called suspension. For example, Muddy river water, sand dispersed in water, etc.
Properties of Suspensions:
(a) It is a heterogenous mixture.
(b) Particle size of suspended particles is greater than 10-6m.
(c) Its particles scatter a beam of light passing through it, thereby making the path visible.
(d) The particles of a suspension can be seen with naked eyes.
(e) The solute particles of a suspension can be seen cannot pass through a filter paper. This property is used to separate the components of suspension by the process of Filtration.
The solute particles are left as residue on the filter paper and the liquid passes down and is known as filtrate. This liquid does not scatter light now.
(f) It is unstable and its suspended particles settle down on keeping it undisturbed for sometime.
Colloidal Solutions or Colloids:
when the size of particles of dispersed phase is between 10-9m and 10-6m in a dispersion-medium, then the mixture is called colloidal solution.
Properties of Colloidal Solutions:
(a) These are heterogenous mixture consisting of two phase-dispersed phase and dispersion medium.
(b) The size of particles of a colloid are 10-9m to 10-6m (1nm-1000nm).
(c) Colloidal solution particles are not visible to naked eyes.
(d) Colloidal solution particles can pass through filter paper.
(e) Colloidal solutions diffuse (or migrate) very slowly from a region of higher concentration to a region of lower concentration.
(f) Colloidal solutions are quite stable and the dispersed phase does not settle down on standing.
(g) The colloidal particles always move at random or in zig-zag path, in all directions. The ceaseless movement of colloidal particles in zig-zag path, is called Brownian movement.
(h) When a strong beam of light is passed through a colloidal solution kept in a beaker in dark room, the path of the light through the colloidal solution become visible. This is called Tyndall Effect. This effect is not exhibited by true solutions.
Types of Change:
(a) Physical Change
(b) Chemical Change
Physical Change:
The change in which physical properties of a substance are changed is called a physical change. For example, On heating, ice(solid) changes to water (liquid) and water (liquid) to steam (gaseous state).
(Please Note: In a physical change, chemical composition of the substance does not change and no new substance is produced)
Chemical Change:
The change in which new substances are formed with different properties is called a chemical change. For example, Burning of candle, Change of milk into curd, Cooking of food, etc.
Burning of Candle:
When candle burns, its wax changes into gaseous products (carbon dioxide and water vapor), whose properties are entirely different from that of wax. So, burning of candle is a chemical change.
Characteristics of Chemical Change:
(a) It involves change in chemical composition.
(b) New substance/substances is/are formed, which posses entirely different properties.
(c) The change is permanent, i.e., it cannot be easily reversed.
(d) The change, usually, involves evolution or absorption of considerable amount of energy in the form of heat, light, sound, electricity, etc.
CLASS-9-SCIENCE CH-2-IS MATTER ARROUND US PURE?
WRITTEN BY- SHEELU YADAV
TYPIST BY- SHIVAM TIWARI
