CLASS: IX (A, B, C) SUBJECT: SCIENCE

TEACHER: Mrs. NAMRATA B. MORAL

CHAPTER: IS MATTER AROUND US PURE

UNIT: 2.3 SEPERATING THE COMPONENTS OF A MIXTURE

A majority of the substances occur in nature in the form of mixtures. So

separation is required to obtain the pure chemical substances like elements and

compounds. Separation makes it possible to study and use the individual

components of a mixture. Different methods of separation are required for

different mixtures. The application of different methods depends upon the

following:

(i)The nature of mixtures

(ii)The nature of the solute and solvent

(iii)The physical state of the solute and the solvent

Heterogeneous mixtures can be separated into their respective constituents by

simple physical methods like handpicking, sieving, filtration that we use in our

day-to-day life.

2.3.1 How can we obtain coloured component(dye) blue/black ink:

Activity 2.4 (Page No. 19):

Aim: Separation of dye from blue ink.

Materials required: Beaker, water, watch glass, ink, wire gauze, tripod stand,

Bunsen burner.

Procedure:

(i)We take a beaker and fill it half with water and put a watch glass on the

mouth of the beaker.

(ii)We put few drops of blue ink on the watch glass.

(iii)Then we heat this set-up over a Bunsen burner (we do not heat the ink

directly as it may decompose at high temperature).We see that evaporation is

taking place from the watch glass.

(iv)We continue heating as the evaporation goes on and stop heating when we

do not see any further change on the watch glass.

(v)We record our observations.

Observations:

(i)When ink is heated, water part of the ink gets evaporated and dyes remain in

the watch glass.

(ii)There is residue on the watch glass of the blue dye.

Interpretation:

Ink is a mixture of dye in water. Thus we can separate the volatile component

(solvent i.e., water) from its non-volatile component (solute i.e., dye) by the

method of evaporation.

How can we separate cream from milk?

Filtration method is used to separate the suspended particles from a liquid i.e.,

when the solute particles cannot pass through the filter paper. But it cannot be

applied when the suspended particles are very small i.e., when the solid

particles in a liquid are very small and can pass through a filter paper. So, we

can separate out these small suspended particles by the centrifugation method.

This method is used to separate suspended particles of a substance from a

liquid or mixture of the miscible liquids with different densities. The cream from

the milk is separated by this method of centrifugation.

Centrifugation method is based on the principle that when a mixture in a

centrifuge( a device or a machine for carrying out the process of centrifugation)

is rotated with speed, more dense components of the mixture are forced to the

bottom and the lighter particles stay at the top.

Activity 2.5 (Page No. 19):

Aim: To separate cream from milk.

Materials required: Full cream milk, test-tube, Centrifuge

Procedure:

(i)We take a test tube and fill it with some full- cream milk.

(ii)Using a centrifuging machine, we centrifuge it for two minutes. We can also

use a milk churner if centrifuge is not available.

(iii)We record our observations.

Observations:

We observe cream floating on the surface in the test-tube.

Explanations:

We know that milk is an example of colloid in which the dispersed phase is fat.

When milk is churned or centrifuged, the fat particles come together to form

cream, which is lighter. The lighter cream floats on the surface, from where it is

collected.

Conclusion: Components of a colloid having different densities can be separated

by centrifugation method.

For more applications of centrifugation refer to “Applications” page no.

20.

2.3.3 How can we separate a mixture of two immiscible liquids?

Separation of two immiscible liquid can be done by using the separating

funnel. This method is use to separate the mixture of two liquids which are

immiscible and have different densities. It means a heterogeneous mixture

of two liquids can be separated by this method.

Activity 2.6 (Page no. 20):

Aim: To separate the mixture of two immiscible liquids.

Materials required: Mixture of kerosene oil and water, separating funnel.

Procedure:

(i)We take a separating funnel and pour the mixture of kerosene oil and

water into it.

(ii)We leave the mixture undisturbed for sometime so that separate layers of

oil and water are formed.

(iii)We open the stop-cock of the separating funnel and pour out the lower

layer of water carefully.

(iv)We close the stop-cock of the separating funnel as the oil reaches the

stop-cock.

Observation and explanations:

The kerosene and water form immiscible mixture as they have different

densities. The kerosene has less density as compared to water and so it

floats on top of water and forms a separate layer.

Conclusion:

Two immiscible liquids form two separate layers, so, they can be separated

using a separating funnel.

For applications refer to page no. 20 ‘Applications’.

2.3.4 How can we separate a mixture of salt and camphor?

Sublimation method is used to separate a mixture which contains volatile

and non-volatile solids. It is based on the principle that on heating, the

volatile component will sublime and then condense but the non-volatile

component will remain back.

To separate a mixture of common salt and camphor(Page No. 20):

Materials required: China dish, funnel, wire gauze, cotton plug, Bunsen

burner, tripod stand, mixture of common salt and camphor.

Procedure:

(i)We take the mixture of common salt and camphor in a china dish.

(ii)We place the china dish on the wire gauze kept on a tripod stand.

(iii)We put an inverted funnel on the china dish and close the narrow end

with the help of a cotton plug.

(iv)With the help of a Bunsen burner we heat the mixture and observe

carefully.

https://images.app.goo.gl/SRggP23XB4Bw3YPC8

Observations and explanations:

As the mixture is heated slowly, the camphor starts to sublime (goes into the

vapour state directly). The vapour of camphor rises upwards and as it

reaches the upper narrow portion of the funnel, it gets condensed into solid.

This process continues till the whole camphor sublimes and deposits. The

common salt remains in the china dish.

Conclusion:

A volatile component (camphor) can be easily separated from the non-

volatile component (common salt) by the process of sublimation.

2.3.5 Is The Dye In Black Ink A Single Colour?

Activity 2.7:

Aim: To separate the dyes present in a given ink.

Materials required: Chromatographic jar, Filter paper, glass rod, tape,

distilled water, ink sample.

Procedure:

(i)We take a thin strip of filter paper and draw a line on it using a pencil,

approximately 3cm above the lower edge.

(ii)We put a small drop of ink (water soluble, that is from a sketch pen or a

fountain pen) at the centre of the line and let it dry.

(iii)We then lower the filter paper into a chromatographic jar containing

water so that the drop of ink on the paper is just above the water lavel and

leave it undisturbed.

(iv)We watch carefully, as the water rises up on the filter paper. We record

our observations.

Observations:

(i)We observe that the water in the jar rises up the filter paper by capillary

action.

Capillary action is the ability of a liquid to flow in narrow spaces.

(ii)When water moves up we can see different coloured spots on the paper

at different distances from the reference line.

Explanation:

The ink that we use has water as the solvent and the dye is soluble in it.

When water moves up it takes along with it the dissolved components or the

dye particles. The coloured components that is more soluble in water rises

faster and it produces a spot at a greater height.

Precaution:

The paper should be hung in the jar vertically and the level of water should

be below the pencil mark.

Conclusion:

Different coloured components present in ink can be separated on

chromatographic paper/filter paper due to their different solubility in it.

For more applications of chromatography refer to ‘Applications’ page no.

21.

2.3.6 How can we separate a mixture of two miscible liquids?

The method of distillation 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.

Activity 2.8:

Aim: To separate the mixture of two miscible liquids

Materials required: Round bottom flask or the retort, thermometer, delivery

tube, condenser, stand, wire gauze, tripod stand, Bunsen burner, mixture of

acetone and water, a beaker or a conical flask to store the distilled liquid.

Procedure:

(i)We take the mixture of acetone and water in a round bottom flask and for

measuring the temperature we fit a thermometer in it as shown in the fig

below.

(ii)We put a wire gauze on the tripod stand. We then clamp the flask on the

stand and put it over the wire gauze properly fitted.

(iii)Next we insert the delivery tube along with the condenser as in the

diagram.

(iv)To store the distilled liquid, we place a conical flask or a beaker on the

other end of the delivery tube.

(v)We heat the mixture with the help of the Bunsen burner and observe

carefully.

Observations and explanations:

When the mixture is heated, acetone started boiling first due to its low

boiling point (329 K or 560C) than water (373 K or 1000C). So the

thermometer reading becomes constant at 329 K for some time until the

entire acetone boils and gets converted into vapour. The vapour formed rises

and passes through the condenser tube where it gets condensed as low

temperature is maintained here by running cold water in the condenser.

The condensed acetone vapour gets converted into small drops of acetone

and get stored in the beaker.

The process continues till the whole acetone gets vapourised and condensed.

In this way we get distilled acetone and the water remains in the flask.

Conclusion:

The mixture containing two miscible liquids that boils without

decomposition and have sufficient difference in boiling points(30 K) can be

separated into its components by distillation method.

Fractional Distillation:

If two or more liquids in a mixture have very close boiling points or the

difference in boiling points is less than 25 K or 250C, then the process of

simple distillation cannot be applied to separate them. In this case, Fractional

distillation is used.

The apparatus for fractional distillation is similar to the simple distillation,

except that a fractionating column is fitted in between the distillation flask

and the condenser.

A fractionating column is a tube packed with glass beads. The beads provide

surface for the vapours to cool and condense repeatedly.

Activity to separate the components of a mixture of alcohol and water,

having the difference in boiling point less than 25 K or 250C.

Materials required: Round bottom distillation flask, fractionating column,

condenser, conical flask, thermometer, tripod stand, wire gauze, clamp,

Procedure:

(i)We set up the apparatus for the activity as shown in the diagram below

with the mixture of alcohol and water in the round bottom flask.

(ii)We heat the content of the beaker and observe carefully.

Observation and explanation:

(i)Vapour formed by alcohol and vapour formed by water rises up in the

fractionating column.

(ii)Hot vapour gets condensed at the top of the fractionating column due

to the lower temperature of that zone and gets collected into the round

bottom flask. This happens for the water vapours.

(iii)The vapor of alcohol having low boiling point (315 K or 780C) leaves

the fractionating column through the exit near the top and enters the

condenser (the temperature of the top zone of the fractionating column

reaches 780C). The vapour condenses and the distilled alcohol gets

collected in the conical flask kept at the other end of the condenser.

(iv)The thermometer shows the boiling point of alcohol until all the

alcohol distills over and gets separated. At this point distillation of water

does not take place as the temperature of the topmost zone of the

fractionating column was much less than the boiling point of water (373 K

or 1000C).

(iv)Water vapour gets condensed in fractionating column and returns

back to the distillation flask.

Books consulted for the above notes:

1. SCIENCE Textbook for class IX (NCERT)

2. CHEMISTRY TODAY CLASS IX (Cordova)

3. Sites: eKShiksha

Hasanul007’sBlog-WordsPress.com

NcertHelp

Forum-Byju’s