What is Mixtures
A mixtures consists of two or more substance in any proportion. A mixture can be seperated into pure substances using appropiate seperation technique
Mixtures are Two Types
What is Solutions
A solution is a homogeneous mixture of two or more substances. The major component of a solution is called the solvent, and the minor, the solute.
We can measure the concentration of a solution through the amount of solute present per unit volume or per unit mass of the solution/solvent
What is Suspension
aterials that are in solvent and have particles that are visible to naked eyes, form a suspension. A suspension is a heterogeneous mixture.
What is Colloids
They are heterogeneous mixtures in which the particle size is too small to be seen with the naked eye, but is big enough to scatter light. Colloids are useful in industry and daily life. The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium.
A pure substance may be defined as a single substance (or matter) which cannot be separated by simple physical methods.
Pure substances can be further classified as (i) Elements (ii) Compounds
An element consists of only one type of particles. These particles may be atoms or molecules.
For example, sodium, copper, silver, hydrogen, oxygen etc. are some examples of elements.
It may be defined as a pure substance containing two or more elements combined in a fixed proportion by weight and can be decomposed into these elements by suitable chemical methods. It is important to note that the properties of a compound are altogether different from the constituting elements.
Differences between Compounds and Mixtures
1. In a compound, two or more elements are combined chemically.
2. In a compound, the elements are present in the fixed ratio by mass. This ratio cannot change.
3. They are always homogeneous i.e., they have the same composition throughout.
4. The constituents of compound cannot be separated by physical methods
5. The constituents of compound lose their identities i.e., compound does not show the characteristics of the constituting elements.
1) In a mixture, or more elements or compounds are simply mixed and not combined chemically.
2. In a mixture the constituents are not present in fixed ratio. It can vary
3. Mixtures may be either homogeneous or heterogeneous in nature.
4. Constituents of mixtures can be separated by physical methods.
5, The constituents in mixture do not lose their identities i.e., a mixture shows the
characteristics of all the constituents.
Separation of mixtures
The method to be used for separating a mixture depends on the nature of its constituents. We will consider the following three cases:
Mixture of two solids:
- Mixture of two solids
- Mixture of a solid and a liquid
- Mixtures of two liquids
All the mixtures containing two solid substances can be separated one of the following methods:
Separation by suitable solvent:
- By using a suitable solvent
- By the process of sublimation
- By using a magnet
This method is based on the differences in the solubilities of the constituents of a mixture.
Those mixtures can be separated by suitable solvent in which one constituent of a mixture is soluble in a particular liquid solvent whereas the other constituent is insoluble in it.
Separation by sublimation:
- This mixture is used to separate a mixture of sugar and sand by using water as solvent.
- Mixture of sugar and salt can be separated by using alcohol as a solvent because sugar is soluble in alcohol.
- Mixture of sulphur and sand can be separated by carbon disulphide as a solvent.
This process is used to separate those substances from a mixture which sublime on heating.
ixture of common salt (sodium chloride) and ammonium chloride can be separated by the process of sublimation.
Note: sublimation is the process in which a solid is directly changes into gas on heating without coming in liquid state. For example: camphor, ammonium chloride, iodine, naphthalene etc.
Separation by magnet:
If a mixture contains iron as one of the constituent, it can be separated by using a magnet.
Separation of mixture of a solid and a liquid:
- Mixture of iron filling and sulphur powder/carbon power can be separated by using a magnet.
- In factories scrap iron is separated from the heap of waste material by using electromagnet fitted to a crane.
All the mixtures containing a solid and a liquid are separated by one of the following processes:
- By filtration
- By centrifugation
- By evaporation
- By crystallisation
- By chromatography
- By distillation
Filtration is used for separating insoluble substances from a liquid. This means that a heterogenous mixture of a solid and a liquid can be separated by the process of filtration.
Separation by Centrifugation:
- Mixture of chalk/ sand and water is separated by filtration.
- The used tea leaves are separated from prepared tea by the method of filtration.
Centrifugation is a method for separating the suspended particles of a substance from a liquid in which the mixture is rotated (spun) at a high speed in a centrifuge. By this as a mixture rotated round rapidly, a force acts on the heavier suspended particles in it and brings them down to the bottom of the test tube. The clear liquid being lighter remains on top.
Separation by Evaporation:
- This process is used to separate cream from milk.
- We can separate the clay particles suspended in water by this method.
- Blood can be separated into blood cells and plasma by centrifugation.
Evaporation is used to separate a solid substance that has dissolve in water or any other liquid. This process is based on the fact that liquid vaporise easily. The dissolved substance is left as a residue when all the water or liquid has evaporated.
- The common salt dissolve in water can be separated by evaporation.
- We can separate the coloured component of ink by the process of evaporation.
Evaporation is used from recovering dissolved solid substances from liquid mixtures but the liquid itself cannot be recovered by this method. The liquid vaporises and gets lost to the air.
Separation by Crystallisation:
The process of cooling a hot, concentrated solution of a substance to obtain crystals is called crystallisation. This method is used for obtaining a pure solid substance from impure sample.
Impure copper sulphate can be purified by the method of crystallisation to obtain pure copper sulphate.
- Take 10gm of copper sulphate and dissolve it in minimum amount of water in china dish to make copper sulphate solution.
- Filter the solution to remove insoluble impurities.
- Heat the copper sulphate solution gently on a water bath to evaporate water and obtain a saturated solution. Then stop heating.
- Then allow a hot, saturated solution of copper sulphate to cool slowly.
- Crystals of pure copper sulphate re formed. Impurities remain behind in the solution.
- Separate the copper sulphate crystals from solution by filtration and dry.
Common salt is also purified by the process of crystallisation.
Advantages of crystallisation over evaporation:
Separation by Chromatography:
- Some solids like sugar decompose or get charred (degrade) on heating to dryness during evaporation. There is no such problem during crystallisation.
- The soluble impurities do not get removed in the process of evaporation but such impurities get removed in crystallisation.
Chromatography is a technique of separating two or more dissolved solids which are present in very small quantities.
The separation is based on the fact that though two or more substances are soluble in the same solvent but their solubilities may be different.
The most common type of chromatography is paper chromatography.
For example: black ink is a mixture of several coloured substance or dyes which can be separated by paper chromatography.
- Take a thin and long strip of filter paper. Draw a pencil line on about 3cm from one hand.
- Put a small drop of black ink on filter paper strip at the centre of pencil line.
- When the drop of ink has dries, put the filter paper strip into a tall grass jar containing some water in its lower part. The strip is held vertically by attaching its upper and to a glass rod with cello tape.
- The water is gradually rises up the filter paper strip by capillary action. As water moves up the paper strip, it takes along the dyes present in ink.
- The dye which is more soluble in water dissolve first, rises fast and produced a coloured spot on paper at highest position. The less soluble dyes rise slower and form coloured spot at lower position.
- When the water reaches near the top end of the strip, the strip is removed from the jar and dried. The paper with it separate coloured spot is called chromatogram.
Separation by Distillation:
- Chromatoghaphy is used to separate the solution of coloured substances.
- It is used in forensic science to detect and identify the trace amount of substances like poison in the content of the bladder or stomach.
- It is used to separate the small amounts of products of chemical reactions.
Distillation is the process of heating a liquid to form vapour and then cooling the vapour to get back liquid.
In order to recover both solid as well as liquid from the mixture of solid and liquid, the process of distillation has to be used.
Liquid obtained by condensing the vapour is called distillate.
When the homogenous mixture of a solid and a liquid is hated in a closed distillation flask, the liquid being volatile forms vapour. The vapour of liquid are passed through a condenser where they get cooled and condenses to form pure liquid. This pure liquid is collected in a separate vessel. The solid being non volatile remains behind in the distillation flask.
Separation of mixture of two or more liquids:
- A mixture of common salt and water can be separated completely by the process of distillation.
- Pure water or distilled water is made from tap water by the process of distillation.
All the mixtures containing two or more liquids can be separated by one of the following two methods:
Separation by Fractional distillation:
- By the process of fractional distillation.
- By using separating funnel.
A mixture of miscible liquids is separated by the process of fractional distillation.
Fractional distillation is the process of separating two or more miscible liquids by distillation, the distillate being collected in fractions, boiling at different temperature.
The separation of two or more liquids by fractional distillation depends on the differences in their boiling point.
It is long vertical glass tube filled with glass bead. It is an arrangement for providing diffrenet temperature zone inside it during distillation, the highest temperature being at the bottom of the column and the lowest temperature near its top.
A mixture of alcohol and water can be separated by fractional distillation. The boiling point of the alcohol is 78°C and the boiling point of water is 100°C.
Separation of mixture of gases from air:
- When the mixture is heated, both alcohol and water form vapours as their boiling point approach.
- When the temperature at the top of the fractionating column reaches 78°C then alcohol vapours passes in to the condenser and get cooled and collects in a beaker kept at the end of the condenser.
- When the temperature at the top of the fractionating column becomes 100°C, water vapours passes into the condenser get cooled and condenses. Then it is collected in another beaker,
- The various gases of air (like nitrogen, argon, oxygen, carbon dioxide etc.) are separated from one another by the process of fractional distillation of liquid air because the different gases of air have different boiling points.
- The boiling of Nitrogen is -196°C, boiling point of Argon is -186°C and boiling point of oxygen is -183°C.
- The air is first filtered to remove the dust, water vapour and the carbon dioxide.
- 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.
- Liquid nitrogen has the lowest boiling point, so it is collected first and liquid oxygen has highest boiling point, so it is collected last in the beaker.
Separation by separating funnel:
- Fractional distillation is used to separate the mixture of miscible liquids like acetone and water mixture in the laboratory.
- It is used to separate gases of air.
- It is used to separate crude oil ‘petroleum’ into useful fractions such as kerosene, petrol, diesel etc.
A mixture of two immiscible liquids can be separated by using a separating funnel. This separation depends in the differences in their densities.
In this method two immiscible liquids is put in separating funnel and allowed to stand for sometime. The mixture separates into two layers according to the densities of the liquids in it.
On opening the stop cork of the separating funnel, the lower layer of the heavier liquid comes out first and collected in a beaker then the stop cork is closed. The lighter liquid in the upper layer is collected in a separate beaker by opening the stop cork again.
- To separate the mixture of oil and water.
- In the extraction of iron from the ore, the lighter slag is removed from the top by this method to leave the molten iron at the bottom in the furnace.
1) The number of elements known at present are more than 100.Ninety-two elements are naturally occurring and the rest are manmade.
2) Majority of the elements are solid.Eleven elements are in gaseous state at room temperature.Two elements are liquid at room temperature–mercury and bromine.
3) 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.Other examples of alloy are steel, solder, pewter, duralumin, bronze and amalgams.
4)Air is a homogeneous mixture of a number of gases. Its two main constituents are: oxygen (21%) and nitrogen (78%).
Class 9 Maths
Class 9 Science