click the Bell icon to get latest videos from ekeeda [Music] friends we can determine hardness with different methods so here first we are going to use EDTA method and see what exactly is EDTA and how can EDTA be used to determine the hardness of water in this session [Music] determination of hardness of Water by EDTA method the hardness of water can be determined by following methods there are three main methods but in today's session we are going to study the EDTA method the first is EDTA method used most widely why because EDTA is a substance which can easily help us in determining the amount of hardness that is there in the water or the amount of impurities which lead to hardness of water the second is Ohana's method not used very commonly and the third is also soap titration method which isn't used very commonly that means that today's method is one of the most important methods and that is the reason why in today's entire session we are going to focus on the EDTA method EDTA method and determination of hardness now what exactly is EDTA this is the chemical composition of EDTA now what can we see in it is ch2 ch2 with a nitrogen now nitrogen to complete its entire octet of nitrogen what is an octet octet is eight electrons in an outermost shell if the eight electrons are complete in its outermost shell that nitrogen or that any element will be stable let us see how many electrons does nitrogen have in EDTA so I can see one over here the second one over here that is the lone pair third fourth one shared by ch2 fifth sixth one shared by CH 2 7th and eighth one shared by ch2 so I have one two three four five six and seven eight total eight electrons in the octet of nitrogen and that is the reason why nitrogen is stable over here it is stable with three bonds and one lone pair three bonds with six electrons because each bond is made up of two electrons and then we have a lone pair so six plus two that is eight similarly over here also I have three bonds one two three four five six three ones with six electrons and seven eight is my lone pair it is connected with ch2 c o o h on all the four sides this is my exact chemical formula for e d t a EDTA is a hexadented ligand now what do I mean by hexadeented ligand what is exactly a ligand a ligand is a structure or a chemical formula which needs electrons to it a little again will always form a coordinate Bond what exactly is a coordinate Bond a coordinate bond is sharing of electrons between two atoms of different elements but the electrons will shared by only one of them and that one will generally be a metal that means if I have a metal ion or a metal atom with some other ion or some other atom this other atom will name it as ligand which will be electron deficient it will want electrons it will want to take away electrons from a metal ion why a metal ion or a metal atom because metals are always electron Ridge these metal atoms will share their electrons with these ligands and will try completing their octage or keeping them in a stable state that exactly is a ligand now what do I mean by hexadeented ligands that means it will have six hexamine six dense or six ways in which it can take away electrons or or take away any kinds of ions negative ions from a metal or any other electron Rich substance so EDTA is a hexadented ligand it binds the metal ion in water for example ca2 Plus or mg2 plus to give highly stable shillet complex these metal ions are bonded via oxygen or nitrogen from EDTA molecule now we have seen the structure this is the structure of EDTA now over here I have nitrogen on two sides I also do have oxygen on these four sides and this oxygen and nitrogen which are already present in the edtm makes it an hexadeentricle again and helps in attaching itself to the ca2 Plus or mg2 plus ions which are already present under water therefore this method is called as complex metric titration the formation and structure of complex is shown as below let us see the formation of it over here if you see I have ch2 ch2 n and the both the ends are having a lone pair with ch2coo n a c h two c o h c h two c o o h and c h two c o n a where what I have done instead of the edges over here I have placed it as n a's over here on both the ends I have edges plus this is metal two plus any metal it can be calcium it can be magnesium let us see if this entire thing reacts what will it form what is happening over here this ch2 and this ch2 I have kept them as it is over your but now this nitrogen has lone pair in it that means it can form a coordinate Bond it can become a ligand it can attach itself to whom to the metal two plus ions now this is metal two plus it is two plus that means it needs two eyes of electrons because it is a positive charge that means it is an electron deficient but we have two nitrogens over here both the nitrogens having a lone pair and because of this lone pair this lone pair and go and get attached itself to the metal ion it will share its electrons with the metal and attach it hexadeental ligand is nothing but attaching itself to that metal that is shown over here if you can see this is my M which was 2 plus but now this nitrogen and this nitrogen from your I'm from here which we have drawn here and here will go and attach themselves to that metal after this I also have ch2c double bond o can you see the ch2c double bond o c h two c double bond o now I've not drawn an N A or H over here because that is not important what is important is after the C double bond Row the other oxygen which is there is a coordinate Bond it's very important for us to realize the type of bond that we have we have three kinds of bonds we have ionic bond which are made up of ions are positive ion or negative ion will attach each other and from an ionic bond a covalent bond which is made by two atoms and both of these atoms are very similar in Electro positivities or electronegativities and both of them will share the electrons and will form a bond and the last kind of bond is nothing but my co-ordinate bond these coordinate bonds happen between metal atoms and ligands these bonds are shown by an arrow so over here I have my arrow which is a coordinate Bond and over here all these arrows also show a coordinate bond this is the complex which forms when I have my EDTA reacting with the metal now let us see the principle of EDTA method we saw what actually EDTA is how it looks like we saw the nitrogens with a lone pair we also solve the metal ions that the ca Plus or mg plus we saw how these ligands that is all the nitrogen oxygens present in my EDTA will go and attack it but we do not know why we know what is exactly happening over here let us study the principle of it and study why these things are happening why exactly EDT is being used the disodium salt of ethylene diamine Tetra acetic acid EDTA it's ethylene diamine Tetra acetic acid you will understand the name of it once you see the structure again edts ethylene diamine Tetra acetic acid ethylene ethylene is two carbons we already have two carbons over this and this ethylene the next is dye a mind die a mind what is my amine group nh2 group is my amine group can I have n over here yes we already have no way how many ends do we have we have two ends and that is the reason why it is diamine so die a mind T stands for Tetra dye stands for two Tri stands for three Tetra stands for four that means Tetra means that there are some functional groups which are repeating four times which are those functional groups that is what a stands for acetic acids over here I have acetic acid which has repeated itself four times in the molecular formula or in the structural formula of EDTA and here it goes as over here acetic acid acetic acid acetic acid and acetic acid that is the reason why we have ethylene which is over here diamine 2 ends Tetra that is four times acetic acid one two three four so now with the help of the name we can actually write the formula without even learning it with the help of name e d t a ethylene so I'll just draw two carbons diamine I'll just dot two nitrogens and Tetra acetic acid that means how to draw acetic acid four times on the four sides it's as simple as that so again the dysodium salt of Italy in diamite Tetra acetic acid EDTA forms complexes with ca2 plus and mg2 plus now over here we have written ca2 plus and mg2 plus instead of writing ca2 plus and mg 2 plus we can simply write M plus that is nothing but my metal ion Plus as well as with many other metal cations in aqueous solution thus in a hard water sample the total hardness can be determined by titrating ca2 plus and mg2 plus present in an eloquent of sample with naedta solution using nh4cl.nh4oh buffer solution of pH 10 and erychrome black tea as the metal indicator so where we've already seen the reaction and we have seen that instead of mg2 plus and ca2 plus we have just kept a metal 2 plus and we have taken the sodium EDT I'll just show it to you once again so over here I have taken the sodium edts over here instead of tetra acetic acid two acetic acids have been replaced by sodium and over here I have hydrogen what exactly happens this and this will go and attack the metal ion and even the oxygens from two ends will go and attack me metal ion let us focus on the pH 10 indicator now at pH 10 EBT indicator forms wine red color unstable complex with CA plus 2 and mg plus 2 ions in hard water now let us focus on the pH 10 EBT indicator which was there at pH 10 EBT indicator forms wine red colored unstable complex with CA plus 2 mg plus 2 ions in hard water what is exactly happening over here I have an EBT indicator already present this indicator if we put it in pure water it will not have anything to react with it won't have a calcium ion it won't have a magnesium ion and it will be as it is but if you put it in hot water it instantly reacts with ca2 plus ions and mg2 plus ions and turns wine red into color so because of that we get EBT as wine red into color and we can actually find out that that water is hard water in this way we can actually find out the hardness of water or we can easily find out whether the water is hard water or soft water by using the EDTA method this complex is broken by EDTA solution during titration giving stable complex with ions and releasing EBT indicator solution which is blue in color hence the color change is from wine red to blue blue is evt's own color so EBT itself is blue color when it goes into the hard water it reacts with calcium and magnesium when it reacts with calcium and magnesium it forms wine red in color but when you use the titration mechanism and titrate it with EDTA EDT will titrate it back to its original form that is blue color now whatever I have explained you will see the reaction form of it the first thing I explained you was EBT with calcium and magnesium salts and they will combine together and form a wine red color substance which is unstable let us see that so over here I have mg plus 2 or CA plus 2 plus e b t nh4cl nh4oh the pH is 10 and there's a buffer over here so what is happening over here I am getting mg plus 2 CA plus 2 this is an or mg plus 2 EBT or CA plus 2 EBT it will form a wine colored unstable complex now when this unstable complex this is the first part of the reaction wherein EBT which is originally blue in color is reacting with mg plus 2 and CA plus 2 ions and forming a wine red color unstable product over here now when this is titrated with EDTA solution what will happen instead of this EBT the mg plus one e c a plus two y will get connected to EDTA and will form a colorless table complex and the byproduct will be my normal EBT which was attached to where it will get detached and this will come over here it will be blue colored indicator which will be release so while you're in today's session we studied about what exactly is EDTA the full form of it the formula of it the molecular and the structural formula of it we also studied the principle of EDT as well as the significance of it thank you so much for watching this video stay tuned to ekeeda And subscribe to ekeeda