common laboratory process

Common Laboratory Process

Chapter-6

(a) Define distillation.

Ans.: Distillation : The process, which converts any liquid first into its vapour by the application of heat and then condensing the vapour brings it back into its liquid state, is called distillation.

Distillation of liquid = vaporization of liquid + condensation of vapour.

Example : If water is heated, it first converts to vapour. But when the vapour is cooled, it is again converted to liquid. So, the changes of water into vapour and vaour into water is called distillation.

(b) Draw the picture of folding filter paper.

Ans.: The picture of folding filter paper is drawn below :

(1) (2)

(3) (4)

Fig.: Method of folding filter paper

Answer to the Short Questions


(c) How glass tube is cut?

Ans.: Process of cutting glass :Necessary equipments: A triangular file, glass tube, spirit lamp, asbestos.

Working procedure :(i) We take a clean narrow glass tube and place it on the plain table and hold it press by left hand.

(ii) We place an edged of a file on a part of the tube where we want it to divide and pull the file forward.

(iii) We take the tube in our hand. We place two elder fingers of the two hands on the opposite side of cut mark. We press the body of the glass rod by two elder finger and pull down the two ends of the glass tube. Glass tube will be divided across the cut mark.

(iv) In this way, we make pieces of glass tube according to need. The cut ends of the tube are very sharp. To make it smooth hold on the spirit lamp and rotate slowly.

(v) When the end of the rod becomes red hot we remove the rod and cool it by placing on the asbestos.

Caution :(i) Only one mark is to be given on the body of the tube by file.(ii) We should not touch red hot end of the tube.(iii) We move slowly the end of the glass tube on spirit lamp. Otherwise it may crack.

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General Science: Physics and Chemistry

(d) What is wash bottle?

Ans.: Wash bottle : A flat bottom flask is closed airtight with a cork. Two tubes are penetrated through two bores in the cork. One end of the longer tube goes down near to the bottom of the flask and another tube goes just below the end of the cork. Outer side of long tube remains slanting at 60o

angle and a jet is attached at the end. Second tube is penetrated upto neck of the bottle and outer part remains slanting at 120o angle. This type of bottle is called wash bottle.

Fig.: Wash bottleThe special property of wash bottle is if it is blown at outer end of the small tube there is a strong flow of water through jet.

(a) How will you make a delivery tube if it is not available in the laboratory during the preparation of oxygen? Explain with picture.

Ans.: Delivery tube : The tube from which gas comes out from spherical flask is called delivery tube.The method of preparation of delivery tube is discussed below.

Objective : Preparation of delivery tube.

Necessary equipments : Triangular file, spirit lamp, asbestos, protractor and pencil.

Working procedure :(1) We cut the glass tube of desired length with the help of a file.

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Fig.: Preparation of delivery tube

Answer to the Essay Type Questions


(2) With the help of a protractor we draw on the asbestos sheet an angle of definite size at which we want to bend the tube.

(3) We hold the lean glass tube on the flame by two hands as shown slowly so that all sides are heated equally. We hold the place, where we want to make a bend, on the flame.

(4) When the heated place is soft it will start bending automatically by its own weight. Now the rod is removed from flame in hot condition, we hold the two ends of the rod and give necessary pressure to draw an angle equal to that drawn on the asbestos board. Then we wait until the rod is cooled.

Caution :(1) We should use blue flame for bending tube.(2) We should heat the rod uniformly.(3) Measures must be taken so that the flame can heat the area measuring 4-5cm.(4) Care should be taken so that the bending of the rod is smooth.(5) We should cool the heated tube slowly as far as possible.

b. How is filter paper folded? Explain by drawing picture.

Ans.: Folding the filter paper and replace it to the funnel :Necessary equipments : Filter paper, Funnel, glass rod, stand, a ring, beaker with water.Process work : (1) We make two folds of filter paper as shown in the figure.

(2) Again we fold it into two folds.

(3) We open one side of the four folded paper and keep three fold in one side and one fold in another side to make it like a funnel. Thus a cone with filter paper is made.

(4) The filter paper is placed into the funnel and wet with some water so that the filter is fully attached to body of the

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Fig.: Preparation of folding of filter paper and replace it to the funnel

(1) (2)

(3) (4)


funnel. According to figure we place the funnel in a ring attached with a stand. A clean beaker is placed below.

Caution :1. The filter paper should be folded smoothly.2. Care should be taken, so that the filter paper is not torn.3. Filter paper should be attached with the funnel properly.

c. What are evaporation and condensation? By what name it is called when these two processes occur simultaneously?

Ans.: Evaporation : The process of changing a liquid slowly to its vapour or gaseous state at any temperature is called evaporation. Evaporation is a very slow process.Example : If a small amount of water is kept within a vessel of a large mouth and it is placed in an open space, then the amount of water in the vessel is found of disappear gradually and ultimately the vessel dries.

Condensation : The reverse process in which a substance changes from its vapour or gaseous state to the liquid state is called condensation.Example : If vapour of water is passed into the condenser, the vapour will be converted to liquid again. In this case the change of vapour into liquid is condensation.

When evaporation and condensation occur simultaneously, the process is called distillation, i.e. evaporation of liquid + condensation of vapour = distillation.

d. What is distillation? Describe how from the mixture of copper sulphate and sand all the constituents are separated.

Ans.: Distillation : The process which converts any liquid first into its vapour by the application of heat and then condensing the vapour brings it back into its liquid state, is called distillation.

Distillation of liquid = vapourization of liquid + condensation of vapour.

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Example : If water is heated, it first converts to vapour. But when the vapour is cooled, it is again converted to liquid. So, the changes of water into vapour and vapour into water is called distillation.

Process of separation of copper sulphate and sand from the mixture of copper sulphate and sand :

1. We know cupper sulphate is soluble in water but sand is insoluble. So water is added into the mixture of copper sulphate and sand. We stir the mixture by stirrer. As a result all the copper sulphate will be dissolved.2. We filter the solution with filter paper. After the filtration sand will attach with the filter paper and the copper sulphate solution will fall down at the bottom of the beaker.

3. Now the filtrate of copper sulphate and water is heated. When all the water is vapourised, only copper sulpahte will remain in the beaker as crystal. Now the copper sulphate is collected from the beaker.

Description of the separation process by chart :

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+

Vapourisation

(Copper sulphate + sand) + Water

Copper sulphate solution + sand

Sand (Precipitate) Copper sulphate (filtrate)

Water

Water vapourCopper sulphate solution (precipitate)

+

Filtration


e. What is sublimation? Name four substances that can sublime. Describe with a picture how will you separate ammonium chloride and chalk powder if they are mixed.

Ans.: Sublimation : The process, by which a solid substance is converted into its vapour by heating and then the vapour is condensed back into solid state by cooling without passing anywhere through the intermediate liquid state, is called sublimation. For example – if camphor is heated, it directly converted into vapour rather converted into liquid. Again when it is cooled, it is converted directly to solid.

Name of four substances which are sublime:1. Camphor 2. Iodine 3. Naphthalene 3. Ammonium chloride

Separation process of ammonium chloride and chalk powder : Ammonium chloride is a sublime. But chalk powder does not have the property. So if we sublimate their mixture, they will be separated.

1. We take the mixture of ammonium chloride and chalk powder in a china clay pot and cover them by glass funnel. Funnel is also covered by a wet cloth.

2. We heat the pot.3. After sometime it is observed that all the ammonium chlorides are

attached with the surface of the glass funnel and chalk powder remains in the bottom of the china clay pot.

4. Now we separate ammonium chloride from funnel and chalk powder from china clay pot.

Description of the separation by chart :

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Ammonium chloride + chalk powder

Ammonium chloride

Chalk powder (Precipitate)

Sublimation


1. What is Liebig condenser? Draw the figure.

Ans.: Liebig condenser : It is one kind of condenser instrument which is mainly used to convert the extra vapour into liquid. This instrument is invented by scientist Liebig.

The figure of Liebig instrument is given below :

Fig.: Liebig condenser

Multiple choice questions :1. Tick (√) correct answer.

1. What happens when cork is pressed by squeezer?(a) Cork becomes smaller (b) Cork cracks(c) Cork becomes airtight √ (d) Cork becomes harder and airtight

2. Which process can separate iodine and chalk powder from a mixture?

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Answer to the Extra Questions

Answer to the Objective Questions


(a) Filtration (b) Evaporation(c) Distillation √ (d) Sublimation

3. What is the objective of studying common laboratory process chapter?(a) To know how to make apparatus(b) To memorize and adapt how to make apparatus

√ (c) To work yourself to achieve skill(d) To be interested in science teaching through observation.

4. What is done by distillation?(a) Constituents can be separated from the mixture by filtration

√ (b) Constituents can be separated by successive evaporation and Condensation

(c) To get back solid from the mixture(d) To get back solid from the mixture

5. In the absence of Liebig condenser how distillation is performed in the laboratory?

(a) It is not possible to perform distillation without Liebig condenser√ (b) Alternatively, glass tube bent twice at right angles and cold water is used

(c) Liebig condenser can be bought from the market for the purpose(d) This test can be dropped

2. Fill in the blanks :a. Distillation = evaporation + …………b. Naphthalene, iodine etc. are ………….substances.c. At the time of folding filter paper on one side……..folds and in the

other side………………fold are to be taken.d. The tube, one end of which is narrow and capillary, is called……e. To cut a glass rod………….are needed.f. Liebig condenser is used for ……….

Ans.: a. condensation; b. sublime; c. three, one; d. jet; e. one tripod stand, glass pipe, spirit lamp and asbestos; f. distillation.

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3. Match the left side sentence with right side.Left Right

a. Cork squeezer a. one type of boring machineb. Cork borer b. Liebigc. Sublimation c. distillationd. Liebig condenser d. jet tubee. Evaporation and condensation e. ammonium chloride

f. one type of pressing machine

Ans.: a. Cork squeezer one type of pressing machineb. Cork borer one type of boring machinec. Sublimation ammonium chlorided. Liebig condenser Liebige. Evaporation distillation

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common laboratory process

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