Chapter - 2 Is Matter Around Us Pure

Pure Substance

When a substance has all the constituent particles same and shares a similar chemical nature it is called as a pure substance. in other words, we can tell a substance is a pure single form of matter. A pure substance can be element or compound.

Mixture
When two or more kind of pure form of matter are mixed together it forms a mixture. Such that when water and sodium chloride is mixed together then sodium chloride can be separated from water by physical process, but sodium and chloride is a pure substance and can be separated only by chemical process.

Types of mixture
The types of mixture depend upon the nature of different components by which the mixture is formed.

Homogeneous mixture
A mixture which has a uniform composition throughout such mixtures are called as homogeneous mixture or a solution. salt dissolved in water is an example of solution.

Heterogeneous mixture
A mixture which contains physically distinct part and have non-uniform composition are called as heterogeneous mixture. oil and water is an example of heterogeneous mixture.

Solution
A solution is a homogeneous mixture of two or more substance it has a solvent and a solute as its component. Generally, a liquid either containing a dissolved solid, liquid or gas is termed as a solution. But a solution can also be a solid solution or maybe a gaseous solution. An alloy is an example of solid solution and air is an example of gaseous solution. salt mixed in water is an example of normal solution.

Alloy
Is a mixture of two or more metals or a metal and a nonmetal that cannot be separated by any physical method. Brass is an example of alloy which contains 30% zinc and 70% copper.

Properties of solution
Homogeneous mixture.
Particles of a solution are smaller than 1 NM in diameter.
Does not scatter a beam of light passing through them because of very small particle size.
Solute cannot be separated from a solvent by the process of filtration.

Concentration of a solution
It is the amount of solute dissolved in a solution. relative proportion of solute and solvent can be varied. Solution can be dilute concentrated or saturated.

Various ways of expressing the concentration of a solution

Mass by mass percentage of a solution

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Mass by volume percentage of a solution

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Volume by volume percentage of a

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Dilute solution

When the amount of solute mixed in a solvent is low then it is called dilute solution.

Concentrated solution
When the amount of solute mixed in a solvent is high it is called as a concentrated solution.

Saturated solution.
At particular temperature the amount of dissolved solute in a solution is to such an extent that no more solute can get dissolved at that particular temperature in the solution than it is called a saturated solution.

Suspension
It is a non-Homogeneous system, in this system we notice that solid are dispersed in liquid. In this the solid particles do not dissolve but remain suspended throughout the bulk of the medium. suspended particles are visible with naked eyes. Chalk powder mixed in water is an example of suspension.

Properties of suspension
Heterogeneous in nature
Particles can be seen by naked eyes.
Scatter a Beam of light when passed through it
Solute particles settle down if left undisturbed and can be separated by the process of filtration. It is unstable in nature.

Colloidal solution
In this type of solution the particles are and uniformly spread throughout the solution. but due to the smaller size of the particles the mixture appears to be homogeneous. Milk dissolved in water is an example of colloidal solution.

Properties of colloid
Heterogeneous mixture.
Size of particle too small cannot be viewed by naked eyes.
Particle size Big enough to scatter beam of light passing through it.
Do not settle down when left undisturbed. it is stable in nature.

Separating components of a mixture
Different Method of separation can be used for the separation of individual components from a mixture. Heterogeneous Mixture can be separated by simple physical methods like hand picking, sieving, filtration, etc.

Separation by Evaporation
We can separate the volatile component(solution) from its non-volatile solute by the method of evaporation. solution of Dye and water and the dye can be separated from the water by using the process of evaporation.

Separation by centrifugation
In some mixture solid particles cannot be separated by the filtration technique as the particles are very small. by the process of centrifugation those can be separated. In this process the denser particles are send to the bottom and the lightest particle stay at the top when they are spun rapidly.

Application
Diagnostic Laboratories for blood and urine test.
Used in Diaries and home to separate butter from cream.
Used in washing machine to squeeze water out from the wet clothes.

Separation of two immiscible liquids
This process of separation can be done by using a separating funnel. the principle that works is immiscible liquids separate out in layers depending on their densities. oil can be separated from water by this process. In the separating funnel once the water is dripped down slowly the stopper is applied and the oil above remains back in the funnel.

Application
Separate mixture of oil and water
Extraction of iron from its ore

Separation of salt and camphor
To separate such mixtures that contain a sublimable volatile component from a non sublimable impurity the sublimation process is used. Here in this case we know that camphor changes directly from solid state to the gaseous state so it can be removed from the salt by heating the mixture in a funnel such that the camphor gets accumulated in the cooler part of the inverted funnel.

Separation of different colours in a dye
The different colours used in a die can be separated by using the technique of chromatography. Kroma in Greek means colour. In this technique different types of solute dissolved in the same solvent can be separated easily.

Application
Separate different colours in a dye.
Separate pigments from natural colour.
Separate drugs from blood.

Separation of a mixture of two miscible liquids
To separate two miscible liquids the method of distillation is used. in this process the mixture is heated up to the boiling point such that the boiling point of one liquid is different from the boiling point of the other liquid and then the liquid with lower boiling point starts to evaporate faster which is then captured by cooling down the evaporated liquid in a separate container.

Separate different gases from air
Homogeneous mixture of gases can be separated into its components by fractional distillation. In this we have to take a volume of air then compress and cool by increasing the pressure and decreasing temperature until it turns into liquid air and then warm it up slowly so that fractional distillation column can separate the different gases at different temperature because all the different components of the mixture shares have a different boiling point. Example: oxygen -183^o C and argon -186^o C.

Obtain pure copper sulphate from an impure sample
Pure copper sulphate can be obtained from the impure sample by the process of crystallization which is used to purify solids. In this process pure solid are separated from its solution in the form of crystals. It is a better process than evaporation because some solid may decompose on heating or some impurities may remain dissolved in the solution.

Application
Purification of salt that we get from seawater.
Separation of Crystal of alum from impure samples

Physical and chemical change

Physical Change

Change of State is a physical change because these changes occur without the change in composition that is no change in the chemical nature of the substance. Ice, water and water vapour display different physical property but have the same chemical property.

Chemical Change
Chemical changes bring change in chemical property of matter and that gives us a new substance. Chemical change is also called as a chemical reaction because in this process one substance react with another to undergo a change in chemical composition.

Different type of pure substance

Element
Elements can be normally divided into metals, nonmetals and metalloids.

Metals have the following properties
Metals have lustre or shine
They have silvery grey or Golden yellow colour
Good conductor of heat and electricity
They are ductile
They are malleable
They are sonorous

Nonmetals have the following property
Display a variety of colour
Poor conductor of heat and electricity
Not lustrous, sonorous and malleable.

Compounds
Compound is a substance containing two or more elements chemically combined with one another in a fixed proportion. The composition, colour and texture of a compound is same throughout. the properties of a compound is totally different compared to the properties of the combining elements.