PURE SUBSTANCES - A pure substance is a single and distinct type of material that cannot be separated into other type of matter by any physical process. A pure substance is homogeneous in nature and has definite set of properties like, melting point, boiling point, density, etc.
Pure substances can be further divided into two types: Elements and compounds.
(i) ELEMENTS – Element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions. for example: silver, gold, iron, sulphur etc.
METALS- 70% of the naturally occurring metals are metals.
PROPERTIES OF METALS-
- METALS ARE SOLID AT ROOM TEMPERATURE- Mercury is only metal which is liquid at room temperature.
- METALS ARE MALLEABLE- This means that they can be beaten into thin sheets like silver foils.
- METALS ARE DUCTILE-Metals can be drawn into thin wires.
- METALS ARE LUSTROUS- Metals have shine for example silver has a shining surface.
- METALS ARE GOOD CONDUCTOR OF HEAT AND ELECTRICITY- Aluminium and copper metals are used to make cooking utensils as well as electrical wires.
NON-METALS- Only 18 of the naturally occurring elements are non -metals.
PROPERTIES OF NON -METALS
- NON -METALS CAN BE SOLID, LIQUID OR GASES AT ROOM TEMPERATURE
- NON -METALS HAVE DIFFERENT COLOURS- many of the non -metals have specific colour like sulphur is yellow, graphite is black, chlorine is yellowish green etc.
- NON -METALS ARE NON- LUSTROUS- they have dull appearance sulphur and phosphorus do not have a shining surface but have a dull appearance.
- NON -METALS HAVE LOW DENSITIES- They are generally light element.
- NON -METALS ARE NOT SONOROUS – Non-metals do not produce ringing sound like metals.
METALLOIDS- They exhibit some properties of metals and some properties of non -metals. For example: germanium, silicon, antimony etc.
COMPOUNDS- A compound is a pure substance which is formed by combination of two or more elements in a definite proportion by mass. For example: sodium chloride (NaCl), calcium carbonate etc.
MATTER AROUND US EXISTS AS MIXTURE OF TWO OR MORE COMPONENTS.
MIXTURE- Material which consists of two or more pure substances (elements and compounds)present in any proportion. For example Air is a mixure of many gases such as nitrogen, oxygen, carbon dioxide and inert gas.
CLASSIFICATION OF MIXTURE
1.HOMOGENEOUS MIXTURE- A homogeneous mixture has same composition throughout and there are no visible boundaries of separation between components. They are also known as solution.
Examples are air, petrol, vinegar, coloured glass etc.
2.HETROGENEOUS MIXTURE- A heterogeneous mixture has different composition in different parts and there are visible boundaries of separation between the components. Examples are sand and water, mixture of oil and water etc.
CHARACTERISTICS OF MIXTURE
- A mixture can be heterogeneous or homogeneous.
- In a mixture, components may be present in any proportion by mass.
- A mixture shows properties of its constituents.
- A mixture can be separated by distillation, filtration etc.
- There is no melting and boiling point of mixtures.
SOLUTIONS- A solution is a mixture of two or more substances like lemonade, soda water etc.
COMPONENTS OF SOLUTION ARE SOLUTE AND SOLVENT
Solute- The component of the solution that is dissolved in the solvent is called solute.
Solvent- The component of solution that dissolves the other component in it is called the solvent.
For example: A solution of sugar in water is a solid in liquid solution. In this solution sugar is the solute and water is solvent.
PROPERTIES OF SOLUTION
- A solution is homogeneous mixture.
- The solute particle in a solution easily passes through filter paper.
- The solute particles in a solution cannot be seen with naked eyes or even under microscope.
- Solutions are transparent to light.
- The solute particles in a solution do not settle on keeping. This means that solution is stable.
CONCENTRATION OF SOLUTION-
The concentration of solution is the amount of solute present in the given amount of solution.
Solution can be called DILUTE, CONCENTRATED OR SATURATED solution depending on the amount of solute present in it.
Dilute solution- In a dilute solution there is small amount of solute dissolved in the solution.
Concentrated solution – In concentrated solution there is large amount of solute dissolved in the solution.
Saturated solutions- A solution in which no more solute can be dissolved at a given temperature is called saturated solution.
Unsaturated solutions – A solution which contains solute less than the maximum amount of solute that can be dissolved at a given temperature is called unsaturated solution.
Solubility- The amount of the solute present in the saturated solution at the given temperature is called its solubility.
METHODS OF EXPRESSING THE CONCENTRATION OF SOLUTIONS
Some examples of suspension are:
- Muddy water
- Paints (coloured substances suspended in liquid)
- Lime water (calcium hydroxide suspended in water)
Properties of suspension
- A suspension is a heterogeneous mixture.
- The particles of suspension can be seen by the naked eyes.
- The particles of suspension do not pass through the filter paper.
- The particles of suspension settle down when a suspension is left undisturbed.
- A suspension is not transparent to light. They are, either opaque or translucent.
COLLOIDAL SOLUTION- It is a heterogeneous mixture in which solute particles having size between 1 nm to 100 nm are evenly distributed throughout the bulk of medium. Some examples of colloidal solution are, milk, blood, ink, smoke, mist, shoe- polish, etc.
Components of colloidal solution- As colloidal solution is heterogeneous in nature its components are present in two separate phases: the dispersed phase and the dispersion medium.
- Dispersed phase- The solute like components or the dispersed particles in a colloid form the dispersed phase.
- Dispersing medium- The components in which the dispersed phase is suspended is known as the dispersing medium.
Properties of colloidal solutions
- A colloidal solution is heterogeneous mixture.
- The size of colloidal is too small to be individually seen by naked eyes.
- Colloidal solutions are quite stable which means that the particles do not settle down when left undisturbed.
- When a strong beam of light is passed through a colloidal solution placed in dark place, the path of the beam gets illuminated with a bluish light. This phenomenon is called TYNDALL EFFECT.
- They cannot be separated from the mixture by the process of filtration. A special technique of separation called centrifugation can be used to separate the colloidal solutions.
- Used in diagnostic laboratories for blood and urine test.
- Used in dairies and home to separate butter from cream.
- Used in washing machines to squeeze out water from wet clothes.
- To separate mixture of oil and water
- In extraction of iron from its ore
- Colours in a dye
- Pigments from natural colours
- Drugs from blood
- Amino acid obtained by hydrolysis of protein.
- Different gases such as oxygen, nitrogen and noble gases are obtained by fractional distillation of liquified air.
- Separation of different components of crude oil like gasoline, kerosene oil, diesel, lubricating oils, etc.
OBTAINING DIFFERENT GASES FROM AIR: Air is a homogeneous mixture and can be separated into its components by fractional distillation.
Steps of the process are:
- Air is first filtered and passed through drying chambers to remove moisture.
- Air is compressed by increasing the pressure and is then cooled by decreasing the temperature to get liquid air.
- The liquid air is allowed to warm in fractional distillation tower where gases get separated at different heights.
PURIFICATION OF DRINKING WATER IN WATER WORKS
Drinking water which is supplied in cities by water works carries lots of impurities which should be removed before supplied to homes. This is done by the following processes:
Sedimentation tank- The water from the reservoir is first allowed to stand in sedimentation tank to settle down many suspended solids at the bottom of the tank.
Loading tank – In the loading tank some, alum (PHITKARI) is added to water so that suspended clay particles settle down at the bottom of tank.
Filtration tank – when insoluble solid particles are removed the water is passed through filtration tank which has three layers. At the bottom coarse gravel then fine gravel and at the top it is thick layer of fine sand. These layers act as filters and the impurities retain at the bottom when water rises leaving the pure water at the top.
Chlorination tank – In this water is treated with bleaching powder to make the water clean and fit for drinking.
OBTAINING PURE COPPER SULPHATE FROM IMPURE SAMPLE
The crystallisation method is used to purify solids. Crystallisation is the process that separates a pure solid in the form of its crystals from a solution.
- Purification of salt that we get from sea water.
- Separation of crystals of alum (PHITKARI) from impure samples.
DIFFERENT TYPES OF CHANGES OCCURING AROUND US
- PHYSICAL CHANGE
- CHEMICAL CHANGE
- Evaporation of water or alcohol
- Melting of wax
- Breaking of glass into small pieces
- Glowing of an electric bulb
Chemical change- A change in which one or more substances undergoes a change to form a new substance is called a chemical change.
Some examples of chemical change are:
- Rusting of iron
- Burning of incense stick
- Curdling of milk
- Burning of paper and wood