Explore CBSE Notes

2.  Is Matter around us Pure?

(Science-IX)

Introduction:

We have learnt earlier that "The obejct which occupy space and having mass is a matter. "

Pure Substance: A pure substance consists of a single type of particles and all the constituent particles of that substance are the same in their chemical nature.

Element: An element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions. Examples: Iron, gold, silver, carbon, oxygen, nitrogen and sodium etc.

All metals, non-metals and Metelloids come in elements. 

       

Properties of Metals: 

(1)   These are lustre (shine). 

(2)   They conduct heat and electricity.  

(3)    All metals are malleable and ductile. 

(4)   They are sonorous.

(5)  They have silvery-grey or golden-yellow colour. 

Properties of Non-metals:

(1)   These are not lustrous.

(2)  They are poor conductors of heat and electricity.  

(3)   All metals are not malleable and ductile. 

(4)   They are not sonorous. 

(5) They display a variety of colours. 

Metalloids: Some elements have intermediate properties between those of metals and non-metals, they are called metalloids; examples are boron, silicon, germanium etc.

Compounds : A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion. Examples: Water, Salt, sugar, Alcohal, carbon dixode etc. 

Name of compounds	Composed substance
1.  Water	Two part Hydrogen and one part oxygen
2.  Salt	One part sodium and one part chlorine.
3.  Carbon-dioxide	One part carbon and two part oxygen

Note: Above all substances are composed in definite/fixed proportion. These substances cannot be seperated without any chemical process. All components by which they are made are differ to compound.  

Mixture: Such substances which are composed of two or more than two elements or compound in indefinite proportion are called mixture.

Examples of mixtures:

Sugar in water, 

salt in water,

air, 

Mixture of salt and sand. 

salt and iron fills

soda water.

Differences between compound and mixture: 

 

Mixture	Compound
1. Element or compound just mix together to from a mixture.   2. It does not form a new substance. 3. A mixture has a variable composition. 4. It's components can be seperated by physical methods.   5. A mixture shows the properties of the constituents substances. 6. Components have no fixed proportion.	1. Element react to from new compounds.  2. It is a new sunstance. 3. The composition of each new substance is always fixed. 4. It only can be seperated by chemical process.   5. The new substance has totally different propreties. 6. Components have no fixed proportion.

 

Differences between elements and compounds: 

Elements	Compounds
1. Elements contain single kinds of atoms.  2. They can neither be seperated by physical methods of seperating nor chemical methods.    3. They are basic form of matters.	1. Compounds contains two or more than two kinds of atoms.   2. They can only be seperated by chemical process of seperating.   3. They are mainly made of elements.

 

2. Is Matter around us Pure?

---

Types of Mixtures:

(I) Homogeneous: The mixture which has uniform compositions and its compositions can not be identified seperatly is known as homogeneous mixture. 

Example: Solution of water and salt. 

(ii) Hetrogeneous: The mixtures which contain physically distinct parts and have non-uniform compositions, such mixtures are called hetrogeneous mixtures. 

Examples: sand and salt, sugar and salt, water in oil etc. 

Properties of mixtures:

(i) The components of mixtutes can easily be seperated. 

(ii) Each component has its own charectristics. 

(iii) Components are distinct in ratio. 

Solution: 

A solution is a homogeneous mixture of two or more substances.

Example: Lemon water, soda water etc. 

Solution are found in three states of substances.

(1) Solid solution: Alloys.

(2) Liquid solution: Lemon water.

(3) Gaseous solution: Air. 

• There is homogeneity at the particle level in the solution so that its particles can not be identified in distinct manner. 

Properties of solutions: 

(i) It is a homogeneous mixture. 

(ii) It has homogeneity at particle level therefore its particles can not be seen by necked eyes. 

(iii) The path light can not be seen in solution.

(iv) Solution is stable. 

(v) The solute particles cannot be separated from the mixture by the process of filtration.

Components of Solution:

(1) Solvent: The component of the solution that dissolves the other component in it and it is usually present in larger amount, such component of solution is called the solvent.

Examples of solvents: water, alcohal,  tarpentine oil etc. 

(2) Solute: The component of the solution that is dissolved in the solvent and it is usually present in lesser quantity, such component is called the solute.

Examples of solutes: salt, sugar, soda, potassium permagnete and iodine etc. 

Solubility: The amount of the solute present in the saturated solution at this temperature is called its solubility. 

condition that affect solubility:

(i) Temperature

(ii) Pressure

(iii) Nature of solute and solvent

Concentration: Concentration is special quantity of a substance presents in per unit volume in a mixture. 

In other words: 

The quantity of a substance present in a mixture is called concentration of that substance. 

Concentration of a solution: 

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 is called the concentration of a solution.

Methods to find concentration of a solution:

There are various ways of expressing the concentration of a solution, but here we will learn only two methods.

Two common methods to find concentration of a solution.

(i) Mass by mass percentage of a solution

          

(ii) Mass by volume percentage of a solution

         

Types of solutions: 

(1) Saturated solution: At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution.

In other words,

When no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

(2) Unsaturated solution: If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution.

(3) High/super saturated solution: If the amount of solute contained in a solution is more than the saturated level, such a solution is called high-saturated solution. 

 

Suspension: The hetrogenous mixture in which solids are dispersed in liquids, are called suspensions.

A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension are visible to the naked eye.

Properties of a Suspension: 

(i) It is a hetrogeneous mixture.

(ii) The particles of a suspension can be seen by necked eyes.

(iii) The particles of a suspension scatter a beam of light passing through it and make its path visible.

(iv) A suspension is unstable.

(v) They can be separated from the mixture by the process of filtration.

Colloidal solution: 

The particles of a colloid are uniformly spread throughout the solution. Due to the relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous. But actually, a colloidal solution is a heterogeneous mixture, for example, milk, smoke and fog etc.

Properties of colloidal solution: 

(i) A colloid is a heterogeneous mixture.

(ii) The size of particles of a colloid is too small to be individually seen by naked
eyes.

(iii) Colloids are big enough to scatter a beam of light passing through it and
make its path visible.

(iv) They do not settle down when left undisturbed, that is, a colloid is quite
stable.

(v) They show tyndall effects. 

(vi) Colloidal particles can not be seperated by the process of filteration. 

The components of a colloidal solution: 

(i) Dispersed Phase: The solute-like component or the dispersed particles in a colloid form the dispersed phase.

(ii) dispersion Medium:  the component in which the dispersed phase is suspended is known as the dispersing medium. 

Colloids are classified according to the state (solid, liquid or gas) of the dispersing medium and the dispersed phase.

See this table DIs

Dispersed phase	Dispersing Medium	Type	Example
Liquid  Solid  Liquid  Liquid	Gas  Gas  Liquid  Soild	Aerosole  Aerosole  Emulsion  Gel	Fog, Cloud, mist Smoke, Automobile Exhaust Milk, Face cream  Jelly, Cheese, Butter

 

Tyndall Effect: 

The small particles of colloidal can easily scatter a beam of visible light, this scattering of a beam of light is called the tyndall effect. 

Cause of tyndall efect: This happens due to the scattering of light by the particles of dust and smoke in the air.

This effect is named after the name of the scientist who discovered this effect. 

• Tyndall effect can also be observed when a fine beam of light enters a room through a small hole.
• Tyndall effect can be observed when sunlight passes through the canopy of a dense forest.
• In the forest, mist contains tiny droplets of water, which act as particles of colloid dispersed in air.

General examples of colloids that show the tyndall effect: 

Milk, Face cream, fog, clouds, mist, smoke, shaving cream, milk of magnesia, butter, jelly etc. 

 

2. Is Matter around us Pure?

---

The Separation of components of a Mixture:

Getting individual component from a mixture is known as separation. 

Importance of Separation: 

(i) Different methods of separation are used to get individual components from a mixture. 

(ii) Separation makes it possible to study and use the individual components of a mixture.

Common separating methods: 

(i) Filtration

(ii) Magnetic separation

(iii) Winnowing 

(iv) Decantation

(v) Sedimentation

(vi) Handpicking

(vii) Sieving 

Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration that we use in our day-to-day life.

Sometimes special techniques have to be used for the separation of the components of a mixture.

There are many other important separating methods:

(1) Evaporation

(2) Centrifugation

(3) Seperating funnel

(4) Sublimation

(5) Crystallisation 

(6) Chromatography

(7) Distillation

(1) Evaporation: Liquid substances are heated to get vapourised and other remains particles obtained from mixture in this method. 

Applications: 

(a) Separating the volatile component (solvent) from its non-volatile solute by the method of evaporation.

(b) Obtaining coloured component (dye) from blue/black ink. 

(c) Obtaining salt from sea water. 

(2) Centrifugation : Sometimes the solid particles in a liquid are very small and pass through a filter paper. For such particles the filtration technique cannot be used for separation. Such mixtures are separated by centrifugation.

Principle of Centrifugation: 

When it is rotated very fast the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

Applications:

(a) Used in diagnostic laboratories for blood and urine tests.
(b) Used in dairies and home to separate butter from cream.
(c) Used in washing machines to squeeze out water from wet clothes.

(3) Separating funnel : It is used to separate a mixture of two immiscible (अघुलनशील) liquids, like oils and water. 

Principle of Separating funnel : The principle is that immiscible liquids separate out in layers depending on their densities.

Applications: 

(a) To separate mixture of oil and water.
(b) In the extraction of iron from its ore.

The lighter slag is removed from the top by this method to leave the molten iron at the bottom in the furnace.

(4) Sublimation : In this method we use to separate such components of a mixture that have easily get sublimated, like ammonium chloride, camphor, naphthalene and anthracite.

Applications: 

(a) Salt from mixture of salt and ammonium chloride. 

(b) Iron fills from mixture of iron fills and camphor. 

(6) Chromatography : The method which is used to separates such solutes substances that are dissolved in only one kind of solvent. This method is known as chromatography. 

Principle of chromatography: The coloured component that is more soluble in water, rises faster and in this way the colours get separated.

Applications: 

(a) To separate colours in a dye. 

(b) To separate pigments from natural colours.

(c) To separate drugs from blood. 

(7) Distillation : This method is used to separate a mixture of two miscible (घुलनशील) liquids. This method is called distillation. 

It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.

Applications: 

(a) Distillation is used in food industries for concentrating essencial oils, flavours and alcoholic beverages. 

(b) It is used in laboratory to seperates various miscible components of mixture. 

(c) Methenol or ethenol from water. 

(8) Fractional Distillation: 

To separate a mixture of two or more miscible liquids for which the difference in
boiling points is less than 25 K, fractional distillation process is used, for example, for the separation of different gases from air, different factions from petroleum products etc.

Fractionating Column: The apparatus is similar to that for simple distillation, except that a fractionating column is fitted in between the distillation flask and the condenser. A simple fractionating column is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly. 

Obtaining different gases from air: 

Air is a homogeneous mixture and can be separated into its components by fractional distillation. The air is compressed by increasing the pressure and is then cooled by decreasing the temperature to get liquid air. This liquid air is allowed to warm-up slowly in a fractional distillation column, where gases get separated at different heights depending upon their boiling points.

This process is as below: 

Air 

↓

Liquid air

↓

Obtaining oxygen, nitrogen, arogn and carbon dioxide on their boiling points

(9) Crystallisation : Crystallisation is a process that separates a pure solid in the form of its crystals from a solution.

The crystallisation method is used to purify solids. For example, the salt we get
from sea water can have many impurities in it. To remove these impurities, the process of crystallisation is used.

Applications:

(i) Purification of salt that we get from sea water.

(ii) Separation of crystals of alum (phitkari) from impure samples.

Physical properties: The properties that can be observed and specified like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc. are the physical properites.

Chemical properties: A chemical property of a substance that is observed when substance undergoes a chemical changes. Chemical properties cannot be determined by touching or viewing a sample of substance. 

Some chemical properties are as follows:

toxicity

flammability

heat of combustion

chemical stability

oxidation states

Differences between physical and chemical changes. 

Examples of physical changes: 

Cutting of trees, Making of chair or table, dissolving salt in water, Making of Salad from fruits etc. 

Examples of chemical changes: 

Digestion of foods, Cooking of foods, Rusting of Iron, changing colour of knife after cutting vegitables, buring of coal etc. 

Assignment : 

---

Q1. Which separation technique will you apply for the separation of the following? Write their name only.

(a) Ammonium chloride from a powdered mixture of sodium chloride and Ammonium chloride.

(b) Butter from cream.

(c) Oil from water. 

Q2. Write one property of colloids.

Q3. Write three differences between mixture and compound.

Q4. Classify into elements , compound and mixtures: sodium, Soil, Calcium carbonate, air.

Q5. Which of the following will show Tyndall effect:

(a) salt solution        

(b) milk

(c) starch                   

(d) copper sulphate solution

Q6. What is sublimation? Write the two substances that sublime.