Kerala SSLC Class 9 Solutions for Physical Sciences – Separation of Mixtures (English Medium) Part-1
Why is the paddy winnowed after the reaped stalk bundles are threshed? What happens when it is winnowed? Why?
- When the reaped stalk bundles are threshed there will be plenty of chaff mixed with paddy.
- The dust and chaff which are lighter than paddy will be blown away when the paddy is winnowed after the reaped stalk bundles are threshed.
When paddy is de-husked what we get is rice mixed with bran. How are these separated?
Rice mixed with bran is separated by winnowing or sieving.
Many of the substances which we use in our daily life are found in the form of mixtures. Find out more examples.
- Sugar solution
- Salt solution
- 22 carat gold
- Tap water
- Cough syrup
- Brass, bronze, steel(alloys)
- Fruit juices
- Rice mixed with bran
Many of the substances which we use in our daily life are found in the form of mixtures.
What are the characteristic features of mixtures? Let us conduct an experiment to find out.
Take a teaspoon each of iron powder and sulphur powder in a china dish. Mix them thoroughly. Look at the mixture through a lens. Can you see the black grains of iron and the yellow powder of sulphur?
The characteristic features of mixtures are-
- A mixture contains more than one substance mixed in any proportion. For example: milk, soil, lemon juice etc.
- In a mixture, two or more elements or compounds are not chemically combined together.
- The constituents of a mixture retain their original properties.
- Mixtures are constituted by more than one kind of pure form of matter known as a substance.
- The constituents of a mixture can be separated by using a physical process such as hand picking, filtration, holding a magnet etc.
Yes. We will be able to see the black grains of iron and the yellow powder of sulphur.
Some of the properties of iron and sulphur are given in the table below
What might be the most practical method of separating this mixture?
We can separate a mixture of iron and sulphur powder by using a magnet. This method involves the separation of magnetic particles from non-magnetic particles.
Move a magnet above the mixture of iron and sulphur powder. The iron powder is attracted by the magnet, whereas the sulphur powder is not attracted by the magnet. Hence, it remains in the dish. Using this method, we can separate the mixture of iron and sulphur powder.
Can you suggest other methods of separation of mixtures?
Other methods of separation of mixtures:
- By using a suitable solvent
- Crystallisation and fractional crystallisation
- Distillation and fractional distillation
If the proportion of iron powder and sulphur powder in the mixture is changed, can the same methods be used to separate the components? Why is this possible?
Yes, we can use the same methods to separate the components of iron and sulphur powder even if the proportion is changed. This is because the chemical property and physical state remain the same even though the proportion has changed..
Take a small portion of the iron and sulphur mixture in a test tube and add dilute hydrochloric acid (HCl).
Which is the gas produced? What do you see at the bottom of the test tube? Which component has reacted with the acid?
The iron particles in the mixture react with HCl to produce hydrogen gas. Sulphur remains unchanged and is seen at the bottom of the test tube after hydrogen is liberated.
Take another portion of this mixture in a test tube and add a little carbon disulphide. Shake the test tube gently. What do you observe? Explain.
If we shake the remaining mixture of iron powder and sulphur with carbon disulphide, sulphur gets dissolved, whereas the iron does not. On filtration, iron is obtained as a residue and sulphur is recovered from the filtrate by evaporating carbon disulphide.
We can conclude that a mixture of iron and sulphur powder when subjected to separation by using either a magnet or a suitable solvent exhibited the properties of its constituents iron and sulphur.
On the basis of the above experimental observations discuss the following.
- What is the minimum number of substances necessary to form a mixture?
- What is the required proportionate quantity of each substance?
- Is there any change in the chemical/physical properties of the substances when they are mixed?
- Is the formation of a mixture a chemical change or a physical change?
Note down the conclusions in the science diary.
- A mixture consists of two or more substances.
- It can have components in any proportion.
- Usually there is no energy change during the formation of a mixture. A mixture shows the properties of the constituents present in it.
- Formation of a mixture is a physical change.
Aren’t the components of the mixture used in the above experiment solids? Saline water is a mixture formed from a solid and a liquid. Can mixtures be formed from substances in any physical state? Find more examples and add to the table.
|Type of mixture||Examples
|Solid and solid||Soil, …………., ………….|
|Solid and liquid||Saline water,
|Liquid and liquid||…………., …………, ………….|
|Gas and gas||…………, …………., ………….
|Type of mixture||Examples
|Solid and solid||Soil, iron and sulphur powder, alloys|
|Solid and liquid||Saline water,
Sugar in water, blood
|Liquid and liquid||Alcohol in water, Milk, Gasoline|
|Gas and gas||Air
|Liquid and gas||Soda water, aerated drinks|
List more instances after discussion. Tabulate the method of separation in each instance and also the property on the basis of which the separation is affected. Enter in the science diary.
Difference in the size of the particles
|Stones and paddy in rice||Picking up by hand||Colour, size
Tendency to evaporate
|Iron + sand||‒||‒|
|Sugar + sand||‒||‒|
Difference in the size of the particles
|Stones and paddy in rice||Picking up by hand||Colour, size
|Saline water||Vaporisation||Tendency to evaporate|
|Muddy water||Sedimentation||Heavy particles
|Iron + sand||Magnetic separation
|Sugar + sand||Filter by dissolving in water
|Difference in the size of particles|
- Is it possible to filter clear water from muddy water by using the same type of strainer used for filtering tea?
- If a filter paper is used instead of the strainer?
- No, it is not possible to filter clear water from muddy water. This is because the holes of the strainer are bigger than the size of the particles of muddy water.
- Yes, a filter paper can be used to filter clear water from muddy water.
Arrange the equipment as shown in the illustration, and try to separate by filtration clear water from water in which soil is mixed and water in which chalk powder is mixed.
Why was it possible to separate the water using filter paper?
- Why does one component remain in the filter paper after filtration?
- Write down more mixtures which are separated by using a filter paper.
- Can this method be adopted to separate water and salt from saline water? Explain your answer.
- The size of the holes of a filter paper is very small as compared to the size of the particles in muddy water. The water can pass through the tiny holes of the filter paper, but the solid particles of chalk and sand being large cannot pass through the tiny holes of the filter paper. Hence, they remain on the filter paper.
- The size of every particle is different. Solid particles being large cannot pass through the tiny holes of the filter paper. Thus, one component remains in the filter paper after filtration.
- Mixtures which can be separated using filter paper: Chalk + WaterWood powder + WaterCharcoal + Water
Filtration of residues
Charcoal + Water
No, this method cannot be adopted to separate water and salt from saline water because one of the constituents in the mixture must be an insoluble solid. This is not the case with saline water.
You know that common salt is obtained by the vaporisation of sea water using solar heat.
- What happens to the water when saline water is heated?
- Why is the salt left behind? Is there any method for collecting the evaporated water?
- When saline water is heated, water evaporates and leaves the salt behind.
- The heat of the Sun gradually evaporates the water and common salt is left behind as a solid.In order to collect both salt and water from a salt water mixture (or salt solution), the process of distillation is used.
- Distillation method is used for the separation of components of a mixture containing dissolved solid in a solution in order to collect both the components; or two miscible liquids which boil without decomposition and have sufficient difference in their boiling points.
See the illustration showing the equipment for separating such mixtures.
The mixture (saline water) is boiled in a round bottomed flask
- Which component evaporates, salt or water.
When the vapour passes through the condenser, it condenses and flows into the collecting flask as a liquid.
- What is the substance that remains in the round bottomed flask?
- Water will evaporate.
- Salt remains in the round bottomed flask.
Separation of a mixture of completely miscible liquids
- When the mixture is heated which component boil and evaporate first? Why?
- How can this substance be recovered from the vapour?
- The liquid having a lower boiling point will boil and evaporate first. The boiling point of acetone is 56°C whereas the boiling point of water is 100°C. Therefore, acetone will boil and evaporate first.
- The acetone vapour gets cooled and condenses when it passes through the condenser and can be collected from the condenser outlet. Water is left behind in the distillation flask.This method is also called distillation. It is used for the separation of components of a mixture containing two completely miscible liquids which boil without decomposition and have sufficient difference in their boiling points.
How can the component liquids be separated if there is only a small difference in their boiling points?
- Fractional Distillation method is used for the separation of a mixture containing two miscible liquids for which the difference in their boiling points is very less (generally less than 25°C
- The apparatus used for fractional distillation is similar to the distillation apparatus, except that a fractionating column is fitted between the distillation flask and the condenser.
- A fractionating column is a tube packed with glass beads. The glass beads provide a surface for the vapours to cool and condense rapidly.
- The vapour formed by the boiling of the mixture rises up through the fractionating column, condenses at the respective layers and turns into liquid. Because of the continued heat of the vapour, this liquid vapourises again and it enters the next layer. There the vapour condenses again and this process is repeated.
- Thus, because of repeated condensation and vaporisation, methanol which has a low boiling point enters the condenser in a vapour state, condenses into a liquid and gets collected in the conical flask.
- Later, ethanol can be collected in another flask in the same manner.
- In such a situation where there is only a slight difference in the boiling points of the components, the liquid with the lowest boiling point enters the condenser in the vapour state first.
- It condenses and gets collected in vessels. If there are more than two components in the mixture, they can also be separated on the basis of the increasing order of their boiling points. This method is called fractional distillation.
- Crude oil is a mixture of liquid hydrocarbons which have only a small difference in their boiling points. The components of this mixture such as petrol, diesel, and kerosene are separated by fractional distillation.
- Examples: Separation of a mixture of benzene and toluene, separation of a mixture of water and carbon tetrachloride, separation of components of air, separation of crude oil (petroleum) into its fractions etc.
Some details about the components of air are given in table:
- What is the physical state of oxygen at -182°C?
- And at -184°C?
- Which component has the highest boiling point?
- Which one has the lowest?
- The physical state of oxygen at -182°C is the gaseous state.
- The physical state of oxygen at -184°C is the liquid state.
- Oxygen has the highest boiling point.
- Nitrogen has the lowest boiling point.
See the flow diagram showing the process of separation of these gases.
- Which gas will condense first into liquid state?
- From the liquid mixture which component will evaporate first?
- Which component is obtained first from the fractionating column?
- What will be its state – solid, liquid or gas?
- Which will be the last component obtained? In which physical state?
- As the air is cooled, oxygen gas will condense first into the liquid state.
- From the liquid mixture, nitrogen will evaporate first.
- Nitrogen is obtained first from the fractionating column.
- Nitrogen obtained will be in its gaseous state.
- Oxygen will be the last component obtained. It will be in the liquid state.
The arrangement for separation of the components of such a mixture is shown in the figure.
- Which liquid gets collected at the bottom?
- Why does kerosene remain above water?
- How can the water underneath be removed?
- What if these two liquids were miscible?
- Water gets collected at the bottom in the funnel.
- Kerosene is lighter than water. Hence, it remains above the water.
- Water underneath can be removed carefully with the help of the stopcock (tap) provided at the bottom of the funnel.
- If these two liquids were miscible, then the distillation method could have been used for its separation.
Carry out the following experiment.
Take some black ink in a china dish and heat it. (It is enough to keep the dish on hot sand bath.)
Can you see the vapours?
Once the evaporation stops, remove the dish from the heat source.
- Which could be the substance that has evaporated?
- Is there anything left behind in the dish?
- Is ink a single substance? Or is it a mixture? What is your conclusion?
- Yes, we will be able to see the vapours coming out from the China dish.
- Water evaporated from the China dish.
- Yes, a residue, i.e. the dye of the ink, will be left behind in the China dish.
- Ink is not a single substance. It is a mixture of a dye in water and other solvents. Thus, we can separate the volatile component (solvent) from its non-volatile solute by the method of evaporation.
Take a filter paper strip 1 inch wide and 6 inches long. Put one drop of black ink (from a sketch pen or a fountain pen) at about 1 inch from one end of the filter paper. Allow it to dry for one minute. Take water in a jar. Immerse the filter paper (as shown in the figure) into the water in the jar so that the ink spot is just above the water level Observe carefully as the water rises up through the filter paper.
- Do different colours appear in the filter paper?
- What could be the reason for the colours rising through the paper?
- Yes, different colours appear on the filter paper. The solvent runs over the spot and carries the components of the ink along a distance on the paper, which is indicated by the coloured spots.
- The dyes present in ink are usually a mixture of two or more coloured substances. The water rises through the filter paper by capillary action. As water moves up the paper strip, it takes along the components of dyes present in ink. The weakly adsorbed component rises faster through the paper. Those which are strongly adsorbed rise slowly. In this way, the colours are separated. This method for the separation of coloured substances is termed as chromatography.
Examine some situations where centrifugation process is used and write it in your science diary.
- Separation of butter from cream
- Separation of blood into its components of red blood cells, white blood cells, platelets and plasma in a clinical laboratory
- Used in washing machines and dryers to squeeze out water from wet clothes
- Detection of drug from blood
- Separation of organelles from cells and to isolate nucleic acids