Methods of Purification of Organic Compounds, 12th Chemistry for JEE Main Adv in English | Misostudy

Methods of Purification of Organic Compounds, 12th Chemistry for JEE Main Adv in English | Misostudy

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Check out the online video lecture of Methods of Purification of Organic Compounds – Distillation from chapter Purification & Characterization of Organic Compounds of Chemistry class 12th for JEE Main Advanced preparation prepared by Misostudy’s expert faculties. (

Organic compounds are obtained from natural resources. When these compounds are obtained, they are in their impure form. Hence, several methods of purification of organic compounds, they are sublimation, crystallization, distillation, differential extraction, chromatography.

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hello students welcome to the chemistry sessions I hope everybody is doing great so are you enjoying the techniques that we are doing in the last session we had started off with yes crystallization we had discussed crystallization and relives crystallization along with the simple distillation so I hope everybody has revised all the concepts so what we were doing in this simple distillation before moving on to that I'll just write down what all techniques we have covered we have covered the sublimation right I hope everybody remembers this we have covered the crystallization in the last session crystallization right what else the recrystalization also known as recrystallization here and what else we had started off with a very very simple procedure that is of distillation so I have got a simple one so I've got a simple distillation I have got what kind of distillation I hope everybody has a read it or not so every time whenever I give you homework you need to go through the concept first because that would be pretty easier for you to then follow up the session so here simple distillation we have got we have got fractional distillation right distillation every time I am writing down the incorrect spelling what else we have got we have got reduced pressure it's a very very interesting technique reduced pressure distillation and the last one is what kind of distillation the steam distillation also very popular so as we have discussed about the simple distillation in the last session so what actually the simple distillation is we just boil off the mixture of compounds which are having so here main thing is the boiling point difference must be sufficient enough must be enough that is around 50 to 70 Kelvin an approximate value I'm telling you telling you about so that is the minimum kind of boiling point difference that must be there there why there must be a different difference in the boiling point because if the boiling points are nearby or closer to each other and we have taken up let's just say we have got a round bottom flask here and we take up the mixture let's say of compound a and B 1 is having let's just say a boiling point of 105 degree Celsius and other one is having let's say 1 1 5 degree Celsius so what is the possibility over here the possibility is if we try to boil off the compounds they might be boiling off together and there will be no use of then this technique because it won't be separated we will be getting a vapors which is a mixture of the two again so again we are back to square one we are back to the same position again we need to separate it out via some other technique so that is why we need compounds which are having a difference in the boiling point and what are those compounds can you give me an example so it's ether and ether and toluene that is also mixture they have got sufficient enough difference of boiling points so ether and toluene I've got hexane and Halloween and also I've got a very popular mixture that is of chloroform and aniline so that is also a mixture which is separated so these are some kind of mixtures which are actually separated wire this technique because these mixtures have got sufficient enough difference between the boiling points so I hope everybody's clear with the fact now let's just move on to the fractional distillation we are through with the simple one so let's just move on to the fractional so again we'll be drawing the structure first we'll be drawing the apparatus first then I'll explain you so what is actually the fractional distillation in fractional distillation so basically what we do is we implant we actually put a fractional waiting column fractional ating column we have got a similar kind of an operator that is we take up our B that is the round bottom flask what else we take up we take up a wire goes on which it's kept right so that is the wire goes on which the RB has been kept clear what else we have got we have got a tripod stand so here we have got a stand like that and a burner so we have got a burner also so that is how the burner would be so just draw with me simultaneously so that you have a practice of it so a similar kind of procedure we are following up and what else now here comes the fire we light it up so that is the fire that is the flame we have got and what else we have we have the RB and the RB has got a mixture of compounds here so it has got a mixture of compounds so here is the liquid that we have taken up fine here is the liquid again what do we have we have got a stop called we have got a stopcock over here it's always orange in color orangish red even if you see these in laboratories so that is stopped pork here and what else we have got a tube which is penetrating inside the core and then going inside the round bottom flask so that is our B we name it as RB flask nothing but the round bottom flask what will happen there is a tube inserted in here but not a tube exactly over here what is the difference between the simple distillation and the fractional now we'll see here so here we have got is a column we have got a column over here that is the column that is this is the column over here and here it's again of stop cork over here the column has got something in it let us just see what is that so it has got some weeds in it some crystals in it so these are the kind of beads which are present which are actually what the beads are doing whenever the liquid boils off so whenever the liquid boils up from the round bottom flask it goes into the fractionating column it has got so many kinds of glass bead that the surface area or the traveling time of that vapor increases and that means what those kind of liquids which are having the closer boiling points will actually be separated very efficiently via this technique so what is happening here is let me just draw more some more glass plates over here now that is how the glass beads are so these are glass beads increasing the surface area basically what will happen the liquid will then again boil off goes into the condenser gets condensed and finally into some kind of container we have got so what is that container that container will look like somehow like this it may be a conical flask that we can take up like that so that is how the conical flask go to be so that is the conical flask we have got and what else we have got the pure liquid what are we missing out we are missing out the condenser part right so just try to draw the condenser along with me the condenser has got an inlet and an outlet so that is the inlet and that is the outlet here now what does the procedure see here also what we are missing out again is a thermometer a thermometer is also kept over here along with a fractional eating column we have got I'm just making because there's not enough space so I'm just making the thermometer like that so that is a thermometer fine that is the water condenser so always and always mark the things so we have got a mixture of compounds over here mixture of compounds and that – let's just say a and B the difference between the boiling points in the mixture of compounds here in the case of fractional distillation is approximately n – 30 gallons not more than that so here the boiling points are closer so that is boiling point difference between the two that means the boiling points are boiling points are closer to each other fine so that is the entire technique over here what do we do let us just discuss that I hope everybody has drawn it out now we have got a round bottom flask in round bottom flask we take up the mixture of the compounds that we need to boil up that we need to separate what we are doing is the purification technique we are separating out the compounds with purity so we obtain pure compounds over here in this technique as well if any kind of impurities is present that will remain as it is in the RB flask so that is what it is so we take up a mixture here not in the case of simple distillation in simple distillation we had taken up the boiling points which are the boiling point difference which is quite large because we need to separate it out the liquids one by one we do not have any kind of source other than that over here I have got a source what kind of a source we have we have got a fractional aiding column reaction relating all oh yeah and this column what it does is whenever the liquid gets heated up like that it moves into this fractional ating column it travels so long that the temperature keeps on rising in the Army flask so what happens is first of all if I just assume that the boiling point of a is greater than boiling point of B right so which will boil off first the one having the lower boiling point so this one so it will boil off first the B will be traveling and traveling in the fractionating column slowly and slowly the procedure is very slow so it just travels and travels till the time what happens is the temperature here rises so much that a starts boiling off and when the air starts boiling off the B has almost reached at the top so B has got time to travel up and then gets condensed before mixing with the vapors of a right so we are actually increasing the traveling time we are actually increasing the surface area so here the surface area is increased the traveling time is increased and when it reaches the top when the B reaches the top it gets enough temperature it gets enough time for the a to boil off finally the B condenses off first the B condenses off first and then gets collected over here and again what happens then a will start boiling off after some time so it will boil off and then gets collected so that is how the different liquids get collected and since the liquids are actually having a very very less difference of temperatures of boiling points so we cannot use a simple distillation method because that would gave us both the mixtures of pure liquids so we don't want that we want a separate one so here that is how the separation technique is and not only these type of columns we have got different kind of columns so a column would be like this as well so we have got different kinds of formations like this that is how one column could be we need to just provide the enough surface area we need to just provide the enough timing to travel so that is how our main motive is in order to separate so that is how the different kind of columns look like there are hundreds and hundreds of columns available in the market which has got a different kind of structures different kind of shapes present then just in order to have a different kind of attainments different kinds of organic compounds attained so depending upon the criteria depending upon the type of organic compound we want to obtain we use different kind of columns we can choose different kind of columns also there are such columns which are having bulbs like that so that is also column so these are the bulbs these are the different shapes of the columns and I hope everybody has got the procedure what we have done so we have just boiled off and till the time the B rises the B gets collected over here it first condenses then a will come up that is how the procedure is I hope everybody is clear with the fact we are through with the fractional distillation as well what is and where is this technique used so fractional distillation most commonly is used whenever we are separating remember the procedure of pyrolysis you must have done this in lower classes pyrolysis and the breakdown of the crude oil in two different kinds of oils that means kerosene paraffin wax and patrol whatever it is so there are so many kinds of gradations in crude oil we can obtain so many kinds of oils from the crude oil the procedure involves a fractional aiding column a fractionating column just as we have done this here but a quite a bigger one something like this you can say so this column is so big that is it has got so many inlets over here so depending upon the boiling points the liquids will boil off and then condense from different outlets and the different outlets actually attain or obtain a different kind of oil stem so that is used it is so let me just try it over here fractional distillation used in separation of different products products from crude oil you must have recalled the concept that is the cracking of hydrocarbons so yes so we have done this already so I hope everybody is clear with the idea now let's move on to the next one what is the next one is the reduced pressure distillation what is reduced pressure distillation this particular distillation is actually used whenever we are having so much of high boiling point for a compound that we cannot just heat the RV and then obtain it so in order to that what we do is we reduce the pressure of the liquid on the surface of the liquid and it boils off that means we are in turn reducing the boiling point so here is the technique the distillation technique most suited for separating glycerol from spent lye in the soap industry is so first of all let us just analyze what the question says so they are asking about some kind of distillation technique and what we have done so far is different kind of distillation techniques which are given over here so suited for separating now we need to separate glycerol from the spent light what is this particular thing glycerol from the spent lies basically nothing but the saponification reaction and the spent lye is basically what this pent lye is the alkaline glycerol what is this alkaline glycerol when the fat is converted into saponifies into what is a quantification into the glycerol along with the soap naturally so what is left in the mixture is glycerol along with the soap that is alkaline mixture of both that is known as the spent line so we need to separate it out and we need to take out the glycerol as a whole so for that purpose if I go for the simple distillation so that would be a cumbersome process because simple distillation would be requiring lesser temperatures but if we go on to the boiling point of glycerol so I would like to tell you over here the boiling point of glycerol is approximately 290 degree Celsius right which is quite high so simple distillation will be unable to achieve this much of temperature easily if I go by fractional distillation again it would be a very very improper method steam distillation if I go so steam distillation also it must be having some immiscibility with the steam with in with the water and that is not possible over here because glycerol is soluble in water right so here all of these three methods will be wrong but distillation under reduced pressure which will actually reduce the boiling point of the glycerol and now glycerol can easily boil off easily separated so that is what the answer over here is distillation under the reduced pressure so we need to reduce the pressure of the entire reaction mixture reducing the boiling point of the glycerol separating it out clear so answer is D over here let's move on to the next question very next question what does it say a miscible mixture of benzene and chloroform can be separated by so I have given a lot a lot many techniques here so let us just analyze first what benzene is benzene is a non-polar compound right whereas chloroform will be polar but they are saying over here is a miscible mixture they have taken that means they have taken both of them in such a quantity that they are miscible with each other so there's no point of sublimation because sublimation is solid to vapor conversion right so here both of the things are in liquid state chromatography again we are not sure about what kind of adsorption will be there on the stationary phase crystallization what is crystallization we need to first dissolve it into some solvent but these are itself liquids so how can that be possible and now comes up the distillation and also I would like to tell you a point over here in crystallization is if I've got a liquid only and then I boil off then I heat it out with some kind of solvent what will happen if I then try to cool it down again I will be getting the liquid and not the crystals so the condition for crystallization is we must be having what a boiling a melting point right melting point a higher then the room temperature right so that is how we can obtain some crystals at room temperature for that substance so this crystallization is also not applicable because here both of them are liquids benzene is a liquid and chloroform is also a liquid at room temperature now comes up the distillation so if I look at the boiling points the boiling points of benzene so it will be around 80 degrees Celsius whereas for the chloroform it's around 60 degree Celsius so there is a difference of 20 degree Celsius boiling points so right we can apply we can take out the method of distillation for the separation and to be very precise I can also use the method for fractional distillation because the two boiling points are closely related right so I can have to be very precise steam distillation sorry non the steam but the fractional distillation over here and thereby the correct answer is d i hope everybody has got it which of the following compounds gives blood red coloration when it's lust signs extract is treated with alkali and ferric chloride right so again the question for assigns extract a very very famous la signs extract an organic compound and organic solution that is used to detect the various elements present in the organic compound right so they are asking about when are we getting the blood red coloration when the lesan extract is treated with alkaline ferric chloride so basically for this particular question you need to have a proper knowledge about what all reactions are happening so I've got the le right I need to react it with alkali and then ferric chloride so how do we get the blood-red coloration that is the question over here so the blood red coloration how does it observe how it's get observed is the Le should be in the form of first of all any Sen right sodium thiocyanate so that is the Le which is need to be there and when this le reacts with Fe 3 plus ions it will give what it will give the blood red coloration now what is the compound which is formed so that is the compound which is formed which actually is responsible for the blood red coloration into the solution so that is blood red coloration right so what we need over here is in this particular reaction in this particular reaction we need to form Sen that is thiocyanate and for this SCN we need to have s c and n all the three elements present in the reaction side right so out of these three out of these four options what is the answer so first of all if I consider the IOU urea you need to have a proper information about what is the structure of all of these compounds how you do looks like this next is diphenyl sulfide so I hope everybody knows what dye self diphenyl sulfide if if not you can just very easily form the formula so that is the structural formula for it diphenyl hydrazine if you just look here very carefully in diphenyl hydrazine as well you will not found it you will not find any sulfur present over here right so there is no sulfur present right in bends amide as well no sulfur over here sulfur is present but nitrogen is not present so no nitrogen and it is the only a option in which nitrogen carbon as well as the sulfur is present that is what we need in the particular reaction getting the blood red coloration so we need sulfur carbon and nitrogen whenever a question pops up about what all compounds will give the blood red coloration you need to just see which compound contains all the three that is sulfur carbon and nitrogen is the important thing over here I hope everybody now remembers it is the correct option now let's move on to the next question so what does the next question say okay now it's the type of multiple type question multiple choice sodium fusion extract obtained from aniline what is sodium fusion extract that is lel assigns extract obtained from the aniline on treatment with iron sulfate and sulfuric acid in the presence of air gives Prussian blue crucian blue color again it will remind you of what the test for the nitrogen right that is the detection test for nitrogen where we get the Prussian blue color hence the blue color is due to the formation of you need to have a proper knowledge about what all reaction is going on but as you can see it's a multiple choice question so we need to be very careful while choosing our choices right so first of all let us just have the reaction related to it so the reaction is if I get three and negative that is from the le nez and right what was the Le initially taken NaCl it reacts with Fe plus 2 ions right that is coming from the ferrous sulfate and what we get is this is hexa sign of ferret so this is what we get we are not complete yet next is when due to the presence of this sulfuric acid it converts most of the FE 2 plus ions into fe 3 plus so those also react with the compound which is fault for negative plus what Fe plus three ions giving the compound that is Fe for fe CN six whole thrice so that is what we are getting ferry Ferro cyanide right ferry stands for the ferric over here Ferro stands for the ferrous over here right and we need to look for this particular option so if you look for this particular option I will be getting only one as my answer that is a if you go by the other options Fe plus 3 let us just check because this is a multiple choice question so Fe three-plus over here if this is Fe three-plus right that means this will be ferrous because this is to the counter ion is two by the cross multiplication method I have found out that this plus two this cannot be the case again by the cross multiplication plus two again cannot be the case and by cross multiplication yes this is plus three but this would be three minus which is not at all formed in the reaction mixture so this particular multiple this question appeared in the multiple choice question but that is just to confuse you because some of the students might think that there will be multiple answers going on over here so they may mark one or maybe more than one options that would make your answer completely incorrect so you need to be very careful by choosing the options this has got only one answer right right so that is a we have got it already so I hope everybody is clear with it so it is not necessary that each and every multiple choice question will be having multiple answers so you need to be very careful next question says okay now it's the comprehension type question what is the passage over here during the detection of elements by the science test again the sinus tract question the covalent compounds are converted into ionic compounds by fusion with metallic sodium right they've told us the process of what all process is happening in the law science test right the nitrogen sulfur and the halogens present in the organic compound these are the detection of elements via the science test right so in the organic compound are converted into cyanide sulfide and halides respectively we all know that which are then detected by their usual tests so that is they have given just an information about how the license extractors fall and what is the use of this law science extract I hope everybody gets that now let us just check the questions based on it an organic compound containing n c o as an extra elements is fused with the sodium metal and then extracted with water the species which is not present in the solution of the extract so I've got my trojan let me just rub that I've got my Trojan I'm good sulfur I've got oxygen fused it with na what all do we get NaCl and a 2 s right we all know what all are the formations and for oxygen there is no such kind of an interaction with the sodium so then these are extracted with the water I've got an alkali as well right the species which is not present in the solution extract now the solution extract we have formed so these are the species which can be formed over here I can have CN right I can have CN s right I can have sulfide but nitrate cannot get formed over here so that is there is no such possibility of formation of nitrate this can be possible if the sulphur gets hindered with the nitrogen so in that case we get n AC n s right in that case we get this otherwise we can just get the sulphide right and there is no chance of formation of nitrate a nitrate here right so that is the option right so I hope everybody has got it answer number C is the correct one yeah we have ruled out all the other possibilities

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