Lecture 10. Buffered Solutions (Buffers) Pt. 1.

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UCI Chem 1C General Chemistry (Spring 2013) Lec 10. General Chemistry -- Buffered Solutions (Buffers) -- Part 1 Instructor: Ramesh D. Arasasingham, Ph.D. Description: UCI Chem 1C is the third and final quarter of General Chemistry series and covers the following topics: equilibria, aqueous acid-base equilibria, solubility equilibria, oxidation reduction reactions, electrochemistry; kinetics; special topics. Index of Topics: 0:05:18 Identifying Buffers 0:11:20 Weak Acid and Salt Example 0:17:23 What Makes this a Buffer? 0:22:23 Calculating the pH of a Buffered Solution 0:27:22 Designing Buffers at Specific pH Values 0:44:34 Acid Base Titration Curves
Meeting/Interview Lactitol Fixed action pattern Chemistry CHARGE syndrome
Acid Meeting/Interview Weakness Gas Angular mil Pharmaceutical drug Ice front Buffer solution Pentose phosphate pathway Chemistry Buffer solution Periodate
Acetate Weakness Spawn (biology) Fermium Buffer solution Wursthülle Methylgruppe Grammatical conjugation Ageing Molar volume Honduras Marl Mixture Conjugated system Salt (chemistry) Lamb and mutton Ammonium chloride Concentrate Gas Hybridisierung <Chemie> Corticotropin-releasing hormone Chemical reaction Chemistry Buffer solution Combine harvester Hydrogen Sodium Acid Deferoxamine Computer animation Follistatin Orders of magnitude (radiation) Folsäure Generic drug Iron Ems (river) International Nonproprietary Name Salt Base (chemistry) Thermoforming
Weakness Hydrochloric acid Columbia Records Ham Cell (biology) Molar volume Tube (container) Conjugated system Periodate Mineral Process (computing) Chemical reactor Neprilysin Concentrate Solution Chemistry Buffer solution Hydroxide Electronic cigarette Water Hydrogen Acid Initiation (chemistry) Functional group Arachidonic acid Orders of magnitude (radiation) Iron Salt Base (chemistry) Lymphangioleiomyomatosis
Water Acid Concentrate Asset Base (chemistry) Wursthülle Growth hormone Conjugated system Buffer solution
Operon Hydro Tasmania Solution Chemistry Cupcake Protein Transformation <Genetik> Sway bar Periodate Alum Concentrate Chemical property Gas Walking Solution Chemical reaction Hydroxide Death Wine tasting descriptors Vancomycin Acid Phosphate Folsäure Azo coupling Freies Elektron Bottling line Thermoforming Chewing gum Antigen Acetate Weakness Acetic acid Hydroxyl Cave Wursthülle Columbia Records Deterrence (legal) Ageing Cell (biology) Gene expression Molar volume Conjugated system Mineral Process (computing) Area Setzen <Verfahrenstechnik> Essig Phase (waves) Physiology Carbon (fiber) Hybridisierung <Chemie> Buffer solution Pressure Water Combine harvester Sodium Systems biology Initiation (chemistry) Iron Base (chemistry)
Maßanalyse Oxidimetrie Battery (electricity) Surface finishing Highway Addressable Remote Transducer Protocol Gold Lead Ham Chemische Synthese Orlistat Gesundheitsstörung Colourant Molar volume Tool steel Conjugated system Beer Chemical reactor Concentrate Chemical property Walking Gelatin Gezeitenküste Topicity Solution Chemical reaction Buffer solution Kalisalze Acid PH indicator Functional group Alu element Base (chemistry) Mixing (process engineering) Mindestzündenergie
Stop codon Oxidimetrie
OK but I have everyone's attention please I want to make a few announcements before we begin and the 1st is to remind you that you have a mid-term coming up on Wednesday right and you already know all about that assigned the assigned seats for each 1 of you and so please take the time to go to the class website and find your seat assignments the exam is for 45 minutes and so it is very important that I start exempt promptly on time because otherwise it's going to come out of your time and so it's important that you will get the classed as there is a charge of the class seating in on remind everybody that in your seat assignment is between 100 and above all it's the center aisle it is between 0 and 99 and it's an odd number it's on this side not sorry and even numbers on this side and the odd numbers on this side alright so when you come in and it's important that you find seat as soon as possible OK if somebody is in your see it does not mean that you find another it means that you need to let me know because somebody has made a mistake and has taken the wrong seat it's important for me to make sure that I knew I knew correct and the reason for this is their multiple versions of the exam and each of his student ID is linked to a certain exam and so if you're seated in the walls see it means you don't belong exam and that would be considered cheating alright right you have to be seated EU assigned seating OK so please we need to do theirs exponentially and so I need you guys to check ahead of time ,comma few minutes earlier so that you find a seat because as I always tell you on the exact hour I was stopped passing the exams out so you can come a minute before finally see that would be great if you come late I'm going to ask you to stay outside exams and then let you in OK
because I need to make sure for those students who come on time that they have all the possible time to take the exam is echoed evidence no Leslie as far as the content and the exam it will cover everything that we do right up to today right and if you noticed I assigned a last-minute homework that's due tomorrow and buffets and usually I don't do that I don't want to assign homework just before your home or your exam but I have no option because I do want to take a look at those problems before you take the exam because buffers will be on the exams well however when I'm going to be doing is even tho I make the due date for that homework due on Tuesday I just wanted to take a look at it and you don't score so medicine more that's OK because I'll give you the way after the exams you can go in on Thursday or Friday if you wanted to get the best score on the homeward just get another homework are right but I do want you to take a look at this homework so even know that the due date for the homework is to Maurice evening you have some grace period to complete the homework after the exams but I think you should take a look at those problems because they will help you prepare for the exam OK so before I begin on the material today is anybody have any questions great so the last thing I want to mention is that this class is completely full and therefore if you're lieutenant person you may have been assigned the right-handed seat and if you're right-handed person you may have been assigned to a left-handed seat and the reason is that I have no choice because every seat in this room mistaken and so I'm just randomly assigning seats and analysts say that you know grow up and live with it ahead of however if it is going to be extenuating if you find that you it's going to really affect your performance than raise your hand during the exam after you've got your student ID according an exam I'd be happy to move you to somewhere else OK in their seats in the front and I can move you up front but it worth the bother you let me know on the date of the exam came it announced OK so because remember last class we look dead buffers In 1 of the things that you should be able to do is to identify buffet-style you can identify a buffer you need to know what characterizes a buffer and we said the 1st important thing as a buffer
has a weak acid and on weekdays that contradict 1 another so you have to have a weak acid we and they are conjugate to 1 another and we looked at several examples 1 of the examples that we looked at was the weak acid is acidic gasses then
its conjugate base acetate an iron that acetate and I'm comes as assault so you look at the sodium salt of the potassium salt of sodium acetate case so in this case it would be in reality what you have is the weak acid and its conjugate base 10 if you have something like folic acid and you have assaulted that and in reality what you have is the gasses conjugate base or if you have something like ammonium chloride which is the conjugate acid a week base then you would have NH 3 In reality what you have is NH 4 plus an industry in the country at 1 another case no I also see other examples like it might take in each for class and replaced 1 of the hybrid inns with methyl groups so that I have a CH 3 so if you have CH 3 N H 3 C L you see the difference between these 2 is 1 of the hybrid and have been replaced by the industry all right so you have the S and C H 3 and H 2 this would also be a buffer and this is the acid form and this is the conjugate base of that acid interview will look at the combination would the H 3 and H 3 plus can't see 3 it's too all right so if you see something that you haven't seen before you just kind of look at and see that that's very similar to H 4 plus the only difference between the 2 Is that 1 of the hydrogen Senate for Plus has been replaced by 3 so these are all examples of a buffer because you have all you have to have a mixture of both of which could act as a buffer you just have a week Ghassan but you just have to Saltillo it's not a buffer 10 the 2nd thing is that we said they must be in approximately equal amounts are right they don't have to be exactly the same concentrations but they have to be in the right order of magnitude right and they should be In approximately equal amounts into 3 the best buffers are the ones that have them substantial amounts so the 3rd is in substantial amounts and we see a substantial amount we mean higher concentrations are right and if the 3 criteria are met then you know that it's a buffet are right and the last time we said in the way of whole works is that you have called the weak acid Celeste look look at in terms of the generic terms you're weak acid an equilibrium to give you High junior mining inquest plus A-minus requests and I remember the fact that it is a buffer is because you have substantial amounts of theirs and substantial amounts of that so far what do we mean by substantial amounts our 1 1 molar for example is considered a substantial amount case if you take 1 more concentration of each there an equal amount in that would be a good buffet so now you ask itself how does this act as a buffer it acts as a buffer because you had acid so if you add aged 3 0 plus by adding a strong acid now what happens in your high joining my concentration gone so the added acid will react with minor so you have it's 3 0 plus reacting to A-minus to give you age age Class H 2 0 so added
acid is consumed by this reaction because of substantial amounts of B-minus as well the conjugate bases in large amounts and African absorb the added acid and therefore In that way the added acid is consumed and therefore the pH does not change all that much you add various selves you add acid it reacts with the Jeddah-based that
reacts with that Maria substantial amounts of ancient so you added hydroxide iron now it happens there's that weak acid part of it will react with which miners to give you a H 2 0 plus minus all right so this is how buffer access because of substantial amounts of both components 1 component will act to absorb any added and react with the other world function to react with the hydroxide and consume any added hydroxide and the net result is that the pH is not altered very much so we do an example last time where we look at a problem N if you remember we started by saying that you started with 1 molar of the weak acid answered 1 Moeller of the weak acid and . 5 molar of the salt and we said we would set up this equilibrium so we would set up this equilibrium where the beginning you have 1 mullah there's . 5 molar that and then you would solve this in a manner in which it's not any of equilibrium problems are right we know which direction it's going to react but since there is no hard during a mind here it's going to proceed in the forward direction and therefore we know that this will take place in that direction the four-year minus X plus 6 plus 6 she set up the equation software and then you can figure out what the pH of that solutions and recent the pH comes out to be 3 . 4 5 1 so this is the pH about profit now we said in the 2nd part of the problem we said what happens if you add . 1 Waller of a strong acid to this buffer so now we took this buffer and we added .period
1 wall of solution of ABC I know what you look at this year .period 1 mall ACL In 1 leader of the buffer Letson this solution is not in the buffer but let's say we places pure water supply have quite 1 malls in 1 liter of pure water what with the concentration of hydrogen might come up to me .period 1 oversee because hydrochloric acid strong acid dividend associate completely and therefore it can give you a point 1 solution I join you might what is the pH of . 1 . 1 is what tend to negative 1 so what is the picture that solution was so by take this summer 1 of 8 Cl and put it in pure water the pH will change from pH 7 to ph 1 intimacy that so that's a big difference it's 6 orders of magnitude it's going from Pete 7 2 ph 1 sold that gives you an idea that were actually adding a lot of hard invited all right however if we take this amount of during a mind that will place and wanted things about this dramatic change in pH replacing this we capital with the nuclear should be and remember if you take but I don't mind added to undermine would react with its conjugate base to give you the weak gas and water so you were treated like a limiting reagent problem where all the high during mine is consumed and now you're treated like a new initial once had drawn a line is completely consumed this is a new initial World Cup with the pH of the solution so we started with . 5 fold concentration of the salt conjugate base is going to react the high during mine and so at the end even have this is a limiting reactant disoriented .period fight to give me .period of that in overhears the reactor proceeds this way the amount of product will be 1 . 1 0 so now once I had the joining my and my acid concentration and my conjugate base concentrations of changed and this is my new initial and we cannot the pH of the solution and so that I would set about doing this the same way it would solve In the other equilibrium problems so I knew initial would be now 1 . 1 0 the weak acid and . 4 0 of the conjugate base interviews offering it comes out to be pH about 3 . 3 1 all right now I want you to compare this pH with the pH of the buffer that we started with cell here this is the pH of the buffer to begin with this is the pH after you add the acid now the pH has changed at 3 . 3 1 to concede that the changes only small goes from 3 . 4 5 to about 3 . 3 1 so that change in pH is not a big change but remember if the the buffer was not there and yet fuel water it would have changed from pH 7 ph 1 so you can see them out we had a tremendous amount of majority mind and regardless of adding that much of her during a mind you can see that the future will be changed by a very small amount and that's how buffers where they're able to withstand added acid or added base and the pH of the changes very slightly and to put things in that inning but in perspective you will see that that same amount of hydrogen mind would bring about 6 orders of magnitude and changing pH if you were displaced pure water again now it turns out that I want show you you don't want to identify the tube offer you don't have to go through all of this lengthwise process of solving the problem there is a sure way to calculate the pH of a buffer in a minute show you how to calculate the peach of a buffer that's much easier and let's take a generic and example also lets say that I have a weak acid In water giving me 8 3 0 loss to the worst plus but A-minus requests and let's say that's the
case of that assets and we know what makes this a buffer if you have substantial amounts of HGH In substantial amounts of a minor so you have to have both of those and let's say I have 1 more of that in 1 molar of
that to begin with said we're not interested in the concentration of water you have 0 that and therefore we know that we conceded the forward direction therefore this would be minus X plus X plus X so this would be the initial concentrations this would be the change and equilibrium we know the concentration would be 1 minus X this would be acts severe 1 plus acts and we said because these are all week acids and the conjugate bases we know that X is going to be really small each in all of these instances we approximated them to be equal to the initial concentrations are active X is really small then we can make this approximation and what that means is that means this is equal To the initial concentration that you started with and this would be an initial concentration of a minus sign all these problems because they reacted to very small extent we know that that amount of changes can be really really small and so we can
say that the initial concentrations don't change very much right and therefore I consider the quorum expression OK equals high concentration times A-minus concentration divided by age and if we make that approximation we can say this is approximately equal to Hi joining my concentration times the initial concentration in the minors and the initial concentrations of each acid and its conjugate base now remember in all these Buffel problems we are interested in looking at pH are th depends on hydro Newman concentration of I take the high during my concentration on the 1 side and take the other turns to the other side you can we looked at this last time and we said that the high journeyman concentration really depends on this ratio between the weak acid and its conjugate base all right and therefore this is hard during my concentration and I'm interested in looking at pH Soeharto I can retire journeyman concentrations to pH take negative lots if I take the native of the hydro Newman concentration and if I do any operation on this side I need to do the same operation on the other side as well so this would be negative log key Inc now I'm going to log so this is a multiple so in a large-scale as all of you know that becomes a plus cave and I'm going to take the negative log of the ratio of the initial concentrations of the acid to the base all right so now I donated blood had mind turns out to be pH negative log the area would be picky this will give me negative allowed acid Over the conjugate base of the ratio of the initial concentrations of acid To all right and this equation is very very useful because once you know it's a buffer then all you have to do is you want to the pH of buffer you just look at the peak year of the acid minus a lot of the relation of the acid to base a right now if you look at the text book this step this common equation can be written like this .period can also be read like this pH equals PK a plus if I take the inverse of that this I'm becomes a plus so it's long days over acid all right so just stick to 1 of these and I always use in this equation and these equations are called the Henderson house about 2 equations and this is the easiest way to calculate the pitiful buffer alright so so let's go back to that problem that we calculated before the we can do the same thing so just remember that less and you don't have to go through the whole process of setting up the equilibrium expression so we want to apply that equation too this example that we've looked at before you all that you have 1 wall of a seal age in . 5 moles of 8 ceiling added to the water and alluded to 1 liter so we know that the initial concentration of folic acid is 1 molar we know that the initial concentration at the forming an iron because that's assaults and associate completely we know that its concentration is going to be . 5 malls divided by 1 meter which is . 5 smaller they tell us that key aim is 1 . 7 7 times tend to make a formal work therefore we know that if you take the peaking of a solution that the here comes out to be 3 . 7 5 2 all right is at 3 6 Fig number therefore your PTA will go to 3 dB became so now I have everything I need to figure out the key to the solution of the pH would be PKA minus log the concentration of the acid formed divided by the concentration of its conjugate base which it is 3 . 7 5 2 -minus log the acid form would be 1 more letter divided by . 5 more alert so that's too it's a lot you take a lot to me and therefore that comes out to be 3 . 7 5 to minus a 0 . 3 0 1 which gives me a pH of 3 . 4 5 1 so this was a pH of this buffer solution that we calculated before but now you can see it's a lot faster everyone to identify it as a buffer now you can quickly countered with a pH that solution it's not to take the 2nd part to you know that we added Hydro new mines are right and so the 1st for the 2nd time you have to 1st look at the new initial so we know the added high during a minor react what the continent or the acid it would react the conjugate base and so what you do is you could put set up a limiting reagent set up where we know that the conjugate base will react to the high drawing a mind to give you folic acid plus an H 2 0 so we know that before reaction you have the falling iron will be . 5 0 0 more we have a we calculated is to be . 1 0 Moeller and this is 1 more alert and therefore after reaction this would be . 4 0 Moeller This is the limiting reactant given up to 1 . 1 0 molar that a case therefore I can say pH equals minus slogged the concentration of the acid over the concentration of the country's based this is not my new initial so this would be 3 . 7 5 to minus logs at the acid form would be 1 . 1 0 Moeller divided by . 4 0 Moeller are right and as a command to 3 . 7 5 to to minus 1 . 4 3 9 which would give me 3 . 3 1 3 are right but and so once again this gives me the pH of the solutions and therefore this is a much quicker and easier way to figure out where are the key to the solution would turn out to be alright so so we looked at buffers and now you have it's easy way is to figure out the pH of the buffer are right and you should use this on the exam and you see a problem and you identified it's a buffet you don't have to go to working out the entire equilibrium process you can use uses equation and figure it out OK so no 1 will want to looking at something that's very applicable in the laboratory and that is the signing of a buffer a writer will look at designing buffers at Pacific pH values now if you are at all and you recognize that offers a very very important all right if in the laboratory here chemist and in the laboratory in 1 study a reaction that's very very sensitive to changes in high during mine or changes in hydroxide and concentrations in new carrier that reaction a buffer if you're a bottle major you know that very often if you're going to be studying cells for biological systems that are very sensitive to changes in High junior miner hydroxyl concentrations you study them in buffers all right because it turns out that buffers of very important for many biochemical and physiological processes for example district most by chemical transformations are very sensitive to pH and example is your blood give blood arrived the pH of blood is 7 . 4 if by some chance the pH drops to below 7 or it's raised about 7 . 8 sold blood is around 2
. 4 if it drops by .period for pH units and goes to pitch 7 if it drops will to 7 or because about 7 . 8 it brings about instantaneous death are right and because of all the chemical transformations of very sensitive to peach and it turns out then but is a buffer there are carbonates their phosphates proteins in the blood that act as a buffer so you have all the week based and its conjugate acid in equilibrium with each other in the act as a buffer to maintain the pH of the blood at 7 . 4 you are a student is going go on to do you know research that made very often if you're going to study cells and so on you have to carry out the studies and buffers and therefore you should be able to prepare buffers in the laboratory and so when we talk about designing buffers at specific pH this sort of thing is what you do in the laboratory how do you go about designing an appropriate buffer four-year experiment a cake and so let's start like this taking as an example where you want to prepare buffer zone an example is designed as a buffer at pH equals 4 . 6 0 scenario task is that you want to carry out an experiment where you want to maintain the pH at 4 . 6 0 are right so you make a buffer remember the relationship that whenever we deal with Mofaz the relationship that we wanted to keep in mind is pH equals -minus log and Benicia concentration of the acid to finish a concentration the conjugate base now note all of you recognize that there this concentration and this concentration were the same for example let's say I had 1 or more of the weak acids and 1 Waller of its conjugate base they would cancel each other and you end up with 1 here the ratio would be 1 What is logged 1 0 so if you have exactly equal amounts Of the acid and its conjugate base you know that the pH should always equal all right so if you pick any combination so if we go to the table weak acids and the conjugate bases and if you look at that as a member a buffer has several weak acid and a weak conjugate base so that means that the buffer range would involve all right so any 1 of these if you have this is their asses formed as the weak acid this would be a conjugate base so you know that if have equal concentrations of both were think the pH that before we come up to me it's a big game so if I wanted to know if I want to offer at 3 . 7 5 I know that if I take a a one-to-one ratio of these 2 the pitcher that solution with 3 points and 5 invited the city gas said you can see that if I take acetic acid about equal amounts of bold then my pH would be 4 . 7 5 so remember good buffer is 1 in which you have both of them recast its conjugate base 2nd and we want them to be approximately equal concentrations the exactly equal to each other in European was became are right and that everyone substantial amounts so I desired buffers that we want to design has to be 4 . 6 0 and you can see that there is no combination that gives is exactly what we want we local . 6 0 and we don't have any competition that gives us a value that's exactly 4 . 6 0 bravely wanted designer buffer 4 . 7 5 then we all just because the gas and put equal amounts but 1 and 1 more and mix them together and I would have about 4 that's 4 . 7 5 so what I do is then I think the the 1 that has the closest peak value to my desired pH so you look at as we have a couple of choices we have full . 1 9 that's a little far off right we have 4 . 7 to close and we have 4 . 7 5 close and then if you were a 4 . 8 7 a moving too far away so we actually have to potential choices we can put Pick 4 . 7 2 off 4 . 7 5 9 on a pick compounds the weak acid in the week conjugate base that appropriate for your studies sometimes years studying something in buffer reacts to the reaction then that's not a very good buffer in you are studying cells for example and you pick a buffer that's toxic for the cells the new study is out the window because you know your buffer is actually destroying yourselves alright right and therefore it's important that you pick the right combination itself between these 2 you can see that lets it for this study we wanna look at issues and we will look at and but we won a Senate issues we want to maintain the pH of 4 . 6 0 2 can use in between these 2 acetic acid seems a better choice vinegar is is more readily available and we know that it's not going to be a then could inside reactions and so on and so between hybrids or weak acid and acidic gasses a better choice would be something that's more readily available in the lab and and so a city gas would be appropriate choice even we have another 1 that's closer With a Peterson Cassidy because that would be more appropriate for the experiment that you're designing so once you've picked the choice now what you do is you got back and saying so we pick so the 1st job is to pick the conjugate acid the and so Ochoa's is acidic acid and sodium acetate and we know for but this pair PK equals 4 . 7 5 so you have to have a list of the combinations of weak acids and the conjugate bases and you can go through the list to pick out the right choice for your buffer it turns out there are on hand books available that would list out hundreds and hundreds of different types of buffers that you can use and so you pick the appropriate 1 that has the chemical properties that you want as well as the pH so once you've chosen the buffet now you have to figure out how we going to prepare this buffer so that it will have a pitiful . 6 0 so what we now call it is we know that are desired pH is 4 . 6 0 so we say pH equals PKK minus logged now what would a look at his acetic acid 3 C O 2 page that with initial concentration of acetic acid divided by Benicia concentration of its conjugate base is the desired pH is 4 . 6 0 we know that the city as it has a peak year of 4 . 7 5 miners the concentration of acetic acid to the ratio between the 2 so my rear this equation you can see that long Of the ratio of the initial concentration of the acetic acid to its conjugate phase should equal 4 . 7 5 minus 4 . 6 0 which is 0 . 1 5 all right so now I think the inverse logic that I can figure out the appropriate ratio of acid to its conjugate babies and you take inverse log of that that comes out to be 1 . 4 all right so that means that if I wanted to prepare buffer that has appeared to 4 . 6 0 now the ratio has to be 1 . 4 pressure between the acid to its conjugate base it they will want to ratio you know that appear to be cooperative I right but we don't want to appear to 4 . 7 5 and 1 of the pH of 4 . 6 0 and therefore obligations to come out to be 1 . 4 so that means that whatever Botha I prepared it has to have this concentration ratio between the 2 are right so possible the choices would be if I have this signature concentration and my conjugate bears so if I
have let's say 2 . 8 and this would be 2 . 0 bowler so can embrace see that if I have this ratio survive start with an initial concentration of 2 . 8 more alert and to molar that racial comes out to be 1 . 4 surviving mix To What if I take the concentration of the acid in the concentration of the conjugate base and mix them together that would give me a ratio of 1 . 4 all I can say that I wanted to be 1 . 4 and 1 molar that's another possibility you have many options are right or not I can say I want . 2 8 molar Inc . 2 0 Moeller I think Gordon . 1 Moeller and . 1 0 Moeller I write or I can go to .period 0 1 and . 0 1 0 Moeller to see that all of these ratios of concentrations will always give me a ratio of 1 . 4 and all of these buffers would give me a pH a 4 . 6 0 all right but if you look at this 1st member 1 of the properties of the buffer is to be able to withstand added acid base and so what happens there's that higher the Contras remember we expect them to be a substantial amount so what we say is as you increase the concentrations we say that the buffer capacity improves and what is buffer capacity in the buffer capacity but this it is the ability a buffer to withstand added all basis Frederick without being security see that every buffer will have a certain limit and so on it might take this example let's do this buffer if I prepared this concentration this concentration of buffet all right it will have a pH of 4 . 6 0 but 1 that I had 1 molar concentration of high during mine Tuesday by I 1 wall a concentration of joining mind the high joining my concentration is almost 100 times greater than theirs do you think this is going to be able to act as a buffer when you have that much acid added to it so this buffer has very limited buffer capacity because they will be easily swamped by added acid and but if I take 1 more concentration of Newman added to their can you see now it's not going to be swamp because now this is in greater amount than the acid that you're adding so this will have a better buffer capacity and that's what we say you know the 3 criteria for a good buffer is what that they should both have the week gasses conjugate base they I have to be approximately equal amount because the closer they are to each other the PG equals P K R I don't have to be exactly the same because did it to get the desired pH adjusted slightly right but the best ones would be where have go amounts of bold and that we went pitiful speaking and there is substantial amounts and the reason we want substantial amounts of gold is because more we just said and conjugate base that we have the better it's able to withstand added acid based another which buffer capacity is better all right so we need to meet all of these 3 criteria and when we design buffers alright so if you were ever asked designer about where you start with the desired pH and then you go to the list and there are many many less available and the 1st step is to find the appropriate conjugate acid base there all right once you picked that then you can figure out what ratio you need do you need to have both of those who want to figure out the ratio then you have to ask yourself what is buffer capacity that I want all right and if you want a really good buffer capacity then you have to pick ones that have high concentrations of people got it so that kind of finishes up looking and buffers that kind of leads into the next topic gelatin look at itself as far as the midterm his concern you will only have to study at the buffers OK so make sure you review up to buffer is now and will want to looking at the the next topic for the last 5 minutes which is looking some acid-base titration so of look at acid base titration kurds know all of you have seen a titration haven't you can I have a show of hands cool you've seen a titration raise your hands and reducing the titration anti-vice carried out tacticians the laboratory somewhere during this quarter you will be doing titration in the last parliament this week great so the timing is great allowed now when you do a titration all of you know that you start with a direct right and in the view red you place the known concentration so solution with known concentration
and because it's a solution with known concentration we call it the tight Trent are right and In the villain my flask is working In this class is the solution where unknown concentrations and what we call that we call that the and like stay so let's start by saying Why do we wanted the titration titration is are an analytical tool it helps us determine the concentration of a solution right and from that we we can calculate the amount of solutes dissolving that solutions so in order to do a titration we have to take into account a reaction that takes place cleanly without any side reactions so a titration looks at a reaction between the tide turned and the analyze and this reaction has to be a clean reaction without any side reactions taking place are right and we should take advantage of that reaction to figure out how much and liked you have to figure out the concentration of unknown solution so it's an analytical tool that helps you determine the concentration and the unknown solution so in order to figure out when the titration is complete we take advantage of some physical property that reaction sometimes the reactions change color so when the reaction of the 2 reactants have reacted tightened and their allies have reacted completely the completion of that reaction has to be signaled in some way 1 way use signaled the completion is if you have colored react and McKamy actors change :colon write another for you to signal the completion of that reaction is to use an indicator so you added a 3rd region in there and the 3rd reagent changes color all right another way really just have to take advantage of some physical properties another way of figuring out whether the reactors complain is to do a pH titration occurred when you look at that you you follow that especially by acid-base titration is what you do is you follow the pH and when the reaction is complete there is a sudden jump in the pH and look for that sudden jump in the pH and that tells you that the reaction is complete again so ultimately titration as I use as an analytical tool to figure out the concentration of the unknown solution so in any titration you start by putting the known concentrations you have 1 reactor and of no concentration and that goes in the beer you have the unknown concentration and that's the 1 that goes in the last thing we call that the analyze then you have to for that particular we actually have to figure out how am I going to signal when the reaction is complete and taken depending on the reaction you get different way is the most common 1 is to add indicated you at a 3rd reagent that changes color that signals the completion of that reaction right but in this class because we're looking at pH and we've studied pH in detail for us the physical property that we're going to look at is pH arrived and so acid-base titration the completion of the reaction is signaled by a sudden jump in P H Wright and so on examined the pH dependence as tied trend is added to the analyze we're looking at it here the physical property that will look at his pH to the solution and so what we will do is will monitor the pH of the solution as you add more and more tight so the plan the pH of the solutions are right In the flask so a plot of the pH of the solution as a function of the volume of Thai trend it added is called the titration curves are a plot the pH as a function of the volume of added in what we end up with is a titration curves OK so on Friday
will start looking at acid-base titration curves right so I'll stop there today and start looking at this thing going to jail at the same time and