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## Is Matter Around Us Pure Class 9 Notes

MixtureTwo or more substances which have been combined such that each substance retains its own chemical identity.

A mixture is the blending of two or more dissimilar substances that do not chemically combine to form compounds and that can typically be separated by non-chemical means. Examples: Flour and sugar may be combined to form a mixture.

Types of Mixture

Mixtures can be classified into three types: suspension mixture, colloidal mixture or solution, according to how they combine and can be separated.

1. Suspension mixture
A suspension mixture is usually created by stirring together two or more ingredients, where the particles are typically large enough to be seen by the unaided eye or a magnifying glass. The ingredients of a suspension mixture are heterogeneous, meaning that they are not evening distributed throughout. Most mixtures are suspension mixtures.

 Solid-solid mix Solid-fluid mix Fluid-fluid mix Many suspension mixtures consist of solids mixed with solids. Cake mix is an example of visible solid particles mixed together by a means of stirring. Dirt or soil is another example of a solid-solid suspension mixture.These mixtures can be separated by sifting. Sometimes shaking will cause the heavier particles to settle to the bottom. If solid particles are mixed in a liquid or gas to form a  suspension mixture, the ingredients will soon separate, with the heavier solid particles settling at the bottom. For example, if you mixed sand and water, the sand would soon sink to the bottom.If the solid particles are lighter than the liquid–as in the case of sawdust mixed in water–they will separate and float to the top.A major part of air pollution consists of smoke and dust particles mixed within the atmosphere. This is a suspension mixture. After aWhile, the these solid particles will settle to the ground. Besides settling, filtration can also be used to separate the ingredients. If visible globules of a liquid are mixed in a liquid or as solvent, he ingredients will soon separate. If the globules are heavier, they will settle at the bottom. If the globules are lighter, they will float to the top.
2. Colloidal mixture
A colloidal mixture is a homogeneous combination of solid or liquid particles mixed within a liquid or gas solvent.

Properties of a colloid

• A colloid is a heterogeneous mixture.
• The size of particles of a colloid is too small to be individually seen by naked eyes.
• Colloids are big enough to scatter a beam of light passing through it and make its path visible.
• They do not settle down when left undisturbed, that is, a colloid is quite stable.
• They cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation can be used to separate the colloidal particles.

Size of particles

The sizes of solute particles in a colloidal mixture are much smaller than the particles in a suspension, but they are not as small as those in a solution. The particles in a colloidal mixture are typically as small as a clump of molecules that may not even be visible with a common microscope.

What makes a colloidal mixture unusual is that the solute particles do not break down any further to be single molecules–thus forming a solution. Instead, “something” coats the particles and prevents them from completely dissolving in the solvent.

Blending

The blending of materials in a colloidal mixture is usually more aggressive than the simple stirring done in a suspension. Often the material is violently mixed or shaken. A good example is the paint mixer machine that actively shakes the can to thoroughly mix the paint materials to minimize settling.

Some examples of colloidal mixtures are mayonnaise, Jell-O, fog, butter and whipped cream.

Solution

A solution is a homogeneous mixture where one substance is dissolved in another substance. The solute dissolves in the solvent. The solvent is a liquid or gas, and the solute can be a solid, liquid or gas. A solution has a solvent and a solute as its components. The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent. The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute.

Examples:

(i) A solution of sugar in water is a solid in liquid solution. In this solution, sugar is the solute and water is the solvent.
(ii) A solution of iodine in alcohol known as ‘tincture of iodine’, has iodine (solid) as the solute and alcohol (liquid) as the solvent.
(iii) Aerated drinks like soda water etc., are gas in liquid solutions. These contain carbon dioxide (gas) as solute and water (liquid) as solvent.
(iv) Air is a mixture of gas in gas. Air is a homogeneous mixture of a number of gases. Its two main constituents are : oxygen (21%) and nitrogen (78%). The other gases are present in very small quantities.

Properties of a solution

• A solution is a homogeneous mixture.
• The particles of a solution are smaller than 1 nm (10-9 metre) in diameter. So, they cannot be seen by naked eyes.
• 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.

Concentration of a solution

In a solution the relative proportion of the solute and solvent can be varied. Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or a 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. The amount of the solute present in the saturated solution at this temperature is called its solubility. If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution. The concentration of a solution is 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.

Concentration of solution =
Amount of Solution  / Amount of Solute
Or
Amount of Solvent / Amount of Solute

There are various ways of expressing the concentration of a solution.

(i) Mass by mass percentage of a solution =   ${{MassOfSolute} \over {MassOfSolution}} \times 100$

(ii) Mass by volume percentage of a solution =  ${{MassOfSolute} \over {VolumeOfSolution}} \times 100$

Tyndall effect

Tyndall effect can observe when a fine beam of light enters a room through a small hole. This

happens due to the scattering of light by the particles of dust and smoke in the air. It is also known as tyndall scattering.

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.

Dissolving

Dissolving means that after the solute is put in the solvent, it breaks to an atomic, ionic or molecular level and can no longer be seen as a separate entity. For example, mixing the solid material salt into the liquid water results in the salt dissolving into water and creating the salt water solution. The salt breaks into Sodium (Na+) and Chlorine (Cl-) ions within the water solvent.

Polar or non-polar
Typically, all the molecules in a solution are either polar or non-polar. For example, Nitrogen (N2), Oxygen (O2) and Carbon Dioxide (CO2) are all non-polar molecules. They mix well together to form the solution we call air.

Under normal conditions combinations of polar and non-polar molecules do not mix to form a solution. There are exceptions, such as the non-polar Carbon Dioxide dissolving in the polar solvent water (H2O) under high pressure.

Separation
The solute and solvent in a solution cannot be separated unless one of the ingredients changes state of matter. For example, by heating the solution, one material may evaporate. This is also called distillation.

Alloy
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. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition. For example, brass is a mixture of approximately 30% zinc and 70% copper.

Pure Substances
On the basis of their chemical composition, substances can be classified either as elements or compounds.

Element
Element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
Elements can be normally divided into metals, non-metals and metalloids.

Metals usually show some or all of the following properties:

• 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 are gold, silver, copper, iron, sodium, potassium etc. Mercury is the only metal that is liquid at room temperature.

Nonmetals usually show some or all of the following properties:

• They display a variety of colors.
• They are poor conductors of heat and electricity.
• They are not lustrous, sonorous or malleable.

Examples of non metals are hydrogen, oxygen, iodine, carbon (coal, coke), bromine,chlorine etc.

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.

#### Activities

HOW CAN WE OBTAIN DIFFERENT GASES FROM AIR?
Air is a homogeneous mixture and can be separated into its components by fractional distillation.

If we want oxygen gas from air we have to separate out all the other gases present in the air. 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.

HOW CAN WE SEPARATE A MIXTURE OF TWO MISCIBLE 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.

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. 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

HOW CAN WE SEPARATE A MIXTURE OF SALT AND AMMONIUM CHLORIDE?

Real Lab Procedure:

• Place the china dish on a wire gauze that is placed over a tripod stand.
• Cover the china dish with an inverted glass funnel and plug in a little cotton at the opening of the stem of the funnel.
• On heating the mixture in the china dish, white fumes evolve and rise inside the funnel.
• Stop heating when the white fumes stop rising and allow the funnel to cool.
• After cooling, remove the funnel from the china dish and using a spatula, transfer the solid ammonium chloride sticking on the walls of the funnel into a watch glass.

Inference:

• Ammonium chloride sublime and can be separated from the mixture of salt and sand by the process of sublimation.

HOW CAN WE OBTAIN COLOURED COMPONENT (DYE) FROM BLUE/ BLACK INK?

Put a watch glass on the mouth of the beaker as shown in the given figure. Put few drops of ink on the watch glass. Now start heating the beaker. We do not want to heat the ink directly. You will see that evaporation is taking place from the watch glass. Continue heating as the evaporation goes on and stop heating when you do not see any further change on the watch glass.Now we will observe that the water get evaporated from the watch glass and residue is left in the watch glass. This residue is the colored component (Dye). In this way evaporation can used to obtain volatile component from its solution.