Lecture 04. Acids and Bases. Pt. 1.
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Lecture 04. Acids and Bases. Pt. 1.

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4

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26

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CC Attribution  ShareAlike 3.0 USA:
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2013

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English

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Abstract 
UCI Chem 1C General Chemistry (Spring 2013) Lec 04. General Chemistry  Acids and Bases  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 acidbase equilibria, solubility equilibria, oxidation reduction reactions, electrochemistry; kinetics; special topics. Index of Topics: 0:01:31 pH Review 0:05:10 Determining if Solution is Acidic 0:06:52 Strong Acid Characteristics 0:08:22 Showing HCl as a Strong Acid 0:15:00 Percent Undissociated 0:18:51 Finding pOH 0:25:25 Weak Acids 0:27:22 CH5CO2H Example 0:38:24 Ka/pKa Table 0:47:25 Determine if Solution is Basic 0:48:49 Strong Bases

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OK ,comma let's go in and start does anybody have any questions before it begins so I want to remind everybody that members last class I talked about the 5 minutes of a variety that is already in you probably got an email yesterday and so you have a time window to complete and so please make sure that you take the time to complete the survey right OK so you don't have any questions that we can we talk about last time the guys remember the last time
00:52
we looked at the fact that pH the also of minus slots at the height during your mind concentration so we said because the concentrations of hydrogen minds can extend a World Wide range is convenient for us to compress that range to wear to a scale that is more comprehensible to art and the way we do that is by taking the log are right to be converted to a largescale now in this equation and this will his Pete the minus long out of some quantity and so just as we can write candidates we can say he always which equals the
01:46
miners log of the hydroxide and concentration and we can say save PKW is minus log at TWA said he would take a miner's lot quantity there was quite a little history in front of our eyes and ears last time we looked at the fact that kW this is the iron product constant of water and we kW is defined as
02:24
the High junior my concentration times the hydroxide and concentration so I take this equation abiding each 1 of those quantities and take a negative log of abiding kW that would be negative log kW and as all of you know invite an operation on the lefthand side I need to do the same operation on the righthand side Sunderland taken during a mine and that would be the negative log of joining in mind and now multiplying this but we got the logarithmic scale you know that becomes a positive in take apply the same operation to the hydroxide I'm going to be negative log Our hydroxide and concentration and we know that negative lot TW would give me PKW to locates the equals this would be pH plus peel wage all right and that we know that she had W is a constant and 25 results is what is the value of kW it 1 time Cincinnati 14 so I conveyed that PKW it'll be the negative log of 1 times 10 to the negative 14 which gives me In this case is going to 362 number delving 14 are going 3 dB so picky about the 40 so the bottom line is that if he didn't lose 14 we know that th 1st hero wage should equal 14 all right so it appeared to the solution is 1 where that tell me about your weight extracted the 13 to the Cabinet PHS a solution to the to the new the purity test the 12 think so that's easily figures like his remembering that no at the end of last last time we started looking at asset in greater detail you guys remember we said we were going to start looking at acids and bases in greater detail and so we said wouldn't look at passes and we said what defines an acid is that but we can consider it and it was solution is acidic if it contains any High junior mines Over hydroxide In other words a solution acts as an asset is so in other words we can say hi to undermine concentration is greater In the hydroxide and concentration because we know the solution is neutral in the concentration of St. members to take your water pure water is neutral because the during my concentration equals the hydroxide concentration interval the concentration is equal to each other it would be neutral a solution is essential if it contains greater amount 100 new mines will were hydroxide cares about what an acid and we said he'd take acid passengers can be strong for we all right and we look at strong acids last time so they can be the strong acids all week acids and so we take a strong acid and we strong acids we said last time 1 of the things that characterize the strong acid is that in strong acids key is greater In 1 so you you again that acid dissociation constant aid and the case is greater than 1 then we now that is a strong acid to we that strong acids dissociate right for these 2 words are interchangeable so I want to get used to the other terms or finance so associate or ionizing the same things are selling strong acids dissociated or find that is completely now the words of looking at Senate they completely it's almost 100 per cent that would characterize as strong as right it's a strong acid because associates completely and produces an enormous amount of hydrogen lines and that's because it produces an enormous amount of money mine we consider that to be a strong acid so an example of a strong acid we said last time was hydrochloric acid rain in Seattle is hydrochloric acid and if you want show that is a strong asset then we need to write remember we're looking at acidbase equilibrium so we need to look at equilibrium that established when an ACL is placed in water so if you take hydrochloric acid and place it in water equilibrium that will be established were being which are 2nd you tell me what we put on the product sites and you have to be able to write these equilibrium expressions and so what would put on the front side hidden assets so what is an acid produced it's due plus plus mind Coliseum so I call until the acid soil with a policy on mine this babies but because they're contradict 1 another collectivity conjugate base all right so that means that the CIA in water will give me High junior miner plus CEO minus which is the conjugal this an over here I would write down the equilibrium constant which is the acid dissociation constant and that roughly 10 to the power itself to its enormous number and is called life it's called that acid dissociation constant and sometimes you will see some people use the term acid ionization constant the book mean the same thing alright in some textbooks in your text
10:08
textbook would use the word acid association but he will other books and look at some tables they were listed at acid ionization they would mean the same thing all right so I can invited look at the conjugated acidbase pairs here you see that you have the CLC of minus Indiana Condit as this there will be a single lost in each duel right so if this is a strong acid and K is a lot we know that the people will relies entirely on the product side so we say when he was established and you know that it will be a mixture of K is much much greater than what so that's a big number so that means that when he was established a year and a half a lots and lots of geraniums and sealed miners and very little all right and so in fact because is a strong accidents so it might start with let's say initial concentration and let's start with . 1 0 Moeller of the sea in on the product side I have not said it began when I place .period 1 Waller the CEO and strong acid and when he was established say the change would be minus X but we here the last X plus expert resisted Ecuador's 1 2 1 2 1 and we're really not concerned about the concentration of water because it's is such logic sass that it's a constant and therefore we do not include that equipment expression takes the solvent in billions and billions of US upon billions of water molecules and because the water moccasins such large obsessed with the concentration of what it does not change right so since this case is so large we know that we use that the should be equal to . 1 more than in other words the amount that ionizes but the amount that associates because case large and it's on the product side even have a lot of other products being formed and very little reactants over and so it happened is that we say now we go back and equilibrium because of this .period 1 of minus X will approximate 2 0 and that's would be 21 Moeller employment 1 Moeller right because we we know that's because they could be relied entirely on the product side you have lots and lots of products that number is so launched that the amount that slip and associated so small there you can approximate that 2 0 and so all strong acid you concede that the association is complete all right so strong acids dissociate completely and said he wanted to calculate it the percentage of dissociation and I just wanted there's lots of turns you see coming up and they all mean the same thing of using the such association if you see percentage decomposition and you Percent ionization they all mean the same thing are you and what that means there's 1 % actually associated with what was sent actually was consumed and so numerous he said association would be X amount that associated so we always look at it in terms of reactant over where you started with .period 1 more times 100 and remember what is that's equal to for all strong acid it disassociated completely surrounded this would be . 1 more divided by the . 1 times 100 which is 100 per cent so strong acid the Percent association or Percent ionization is 100 cent because of associates completely and salt strong acids and how you identify strong acids it's Kay has to be greater than 1 a case that means that KLA mixture will have a large amount of I don't mind being used right and so but the same compositions will be 100 per cent became now you carried out the online homework sometimes use you have to read the question carefully because sometimes it actually calculated Percent association or adults asks you presented under associated what is percentage that unassociated 7 so the amount of associates is 100 per cent of the amount that's unnecessary 1 0 and so on so you have to read the question carefully because you have to figure out so the same thing you know using problems coming out of it's what is the presented the composition and the ultimate test the waters said that's left on the couple's right which means the amount that's left on reactor in this case because it goes to completion we know that there's hardly any ACL left solution and therefore the amount the percentage that and associated would be zeropercent right not since these of strong acid and we know that associates completely and we know that the had drawn in my concentration here it is . 1 more learned so if we note that high bounce high junior my concentration it is .period 1 more alert we know that the pH of the solution is minus lot of 1 times 10 to the negative ones which means that it equals 1 Sabino said these are kind of countless that he should be able to do immediately without having to write equations you know the Hydra it a strong acid established .period when will the strong acid you don't have write equation you know that associates completely therefore that the strong acid the hydrogen line has to be the amount of the original solutions so for strong acid and this is only the strong acids for strong acids you know that the initial concentration of is equal To the high during my concentration cell during that writing equations you know that he starts with the initial amount of an acid you know that the 100 cottages with same India the Hydra Mount concentration to cap the peaches right now you know the hydrocarbon concentration then you can say the hydroxide and concentration would be kW divided by the majority of my concentration which it is 1 times 10 to the negatives 14 holes where 22 squared divided by the adjoining concentration just . 1 polls leaders and therefore we know that this comes out to 1 times 10 to negative 13 postpone leader on Homola 10 and so it by now
17:55
but the hydroxide and concentration is and I know he'll wait With miners log the hydroxide and concentration which is mine log of 1 times 10 to the negative effect and therefore you know that it's 1 times in a number of adjusting to be anywhere today so that cannot be the team right all you know you know it created you know that feeling is PKW minus create which is 14 minus 1 which gives me creativity work this out in many different ways so you can neither you know the 109 concentration camp about the the hydroxyl concentrations and they've taken lot of that together with your wages on this is that it's much faster you just take the pH and subtracted from 14 and that would give me the same numbers were art so another example of a strong acid would be recorded assets take for chlorine gas this is a formula colleague accent and so the equilibrium that would be established here would be 8 3 0 plus the quest for us C L 4 minus the all right and where we can tell that is a strong acid because it is roughly somewhat similar to 8 Seattle once again this is a strong accent and it is a strong acid then we know that if you start with To begin with if I have 1 chlorine gas and I know that in Calabria some naturalist doubt the change because I know he's a strong acids dissociate completely so this is going to go to 0 and all of this weekend where 2 1 molar and each your class and 1 molar a seal for minors all right so this is once again a strong acid we know strong acids have carried greater than 1 and associates completely right so we know how that the head during a mine concentration the also finish of concentration of chlorine gas said which is 1 more this is 1 molar we know that pH equals 0 are so I want to remind you that th 0 In the held have negative number right so what that means is that it is 0 it has a negative number means it's got to have a really high journeyman concentration by selfcreated is 0 and the pH is 0 interconnected Canadian model that to 0 what will PPO which amount to be foot I'm so this way you should be able to do these calculations very fast to figure out what appeared to be a strong acid is but a high journeyman concentration as strong as it is and what is the hydroxide iron concentration in all which mines are known it turns out that it's going to be hard for you given the formula to figure out whether strong acid or we gasses and and so what I have done as you have noticed on the class website plays a that have acid association constants are at the center where it is that when you look at this list at all I want to look at it the combination South here is the acid form let me everything into this as a conduit acid pair sold in HIV acid you can see that its conjugate base should be I'm online In all the years we must sit out the are right and it's enlisted out so that became values decrease as you go down to the values of the gets smaller and smaller and smaller and so will be here this is trying to undermine selenium continent acid here is junior mind and water became a valuable hydrogen mind is 1 so the ending of world outside highlighted that we all and everything about that will have actually a value greater than 1 all right and so they have a k a value greater than 1 then you know that all of those assets will behave as a strong acid water so what does it mean when say it's a strong acids an associate completely there were going to look at those that have values will relocate 1 cables 1 and those are the ones that are as weak as they don't associate completely and therefore they call we cast right now what color this it's hard for you to see the colors here but I would like you to print this out at home and keep this review because later will look at and then asking the ranging acids all right so you rank the strong acid you see that these are all strong these all colored in red but given the rank university that hydrochloric acid
23:32
is this they're both strong acids hydrochloric acid in Niger strong acids but hydrochloric acid a stronger acid the 900 guests you see them or it take highpriority all right and hydrochloric acid both of these are strong acids but between them and you can see that is a strong message than I conclude that the right to be after rank acids in order of the city then you would use the case values to rank them right and remember who can take the minute lot of if I take the negative log of the game went and that with is thinking and so the use of the rankings in terms of picking as well right so we looked at strong acid is going to look at weak acids are so she strong acids are characterized by 2 important features and 1 of the most important features strong acids have you identify strong acid because you know that there is really no different formulas and the only way that you we give current knowledge can identify strong acid is to look at what stage apparently came to be given to you in the and once you can identified as strong as it once you know the strong acid whilst you know it and Associates completely to remember those who think they should be attractive I understand the behavior of strong acid innocent thing would we get so you take a weak acid all right and In we gasses 2 is less than a right now gave less than 1 million people relies on the reactants sites in other words an equivalent established it less than 1 you know that you're going have lots of reactants and very little product right so now the racial products 2 reactants has changed you have more reactants less products and that's why it's in the gasses and to me gasses and Associates only partially so strong acid associated completely recast its associated partial right so we take an example of a lead acid acetic acid is a weak gas arrived how you know it's a weak acid you know you look at Decatur city Gas said it would be 1 . 7 6 times 10 to the negative 5 malls pollutant all right so unlike having a huge number liked in the past 7 now we have a really small number that is tend to make the fight and you know while a small value for the Indians who know that McCain the equipment constant any :colon constant is only a small number it's much smaller than 1 was that tell you they can have lots of fun reacted reactants and very little products being formed so the mixture equilibrium will have lots of and reacted reactants and their products right now to take acidic gasses and look at its structure you can see that acidic gasses actually has 4 hydrogen are right and number last quarter we looked at what the law structure of acidic gasses and in fact the final exam last quarter and you to draw the Lewis structure and prevent some of its properties based on instruction all right and if you draw the Lewis structure for city gas and this is what it looks like right now if you look at the structure was gasoline see that actually has 4 hydrogen is in that Peru mightily last time that just because a molecule has a hydrogen doesn't mean it's going to be associated with you in class all right it turns out that in the city gas these 3 hydrogen is a very different from the hydrogen attached to that oxygen this hydrogen is the 1 that we're interested and we call them but sociable protesters in other words it's the sociable because the lottery and dissociate can associate come apart right and to recall that at social work time or we also College in the city Proton because that's the only 1 that can actually come off to give you junior mine are these 3 hydrogen as cannot dissociate alright so the properties of the other 3 harvests a very big difference and not every molecule that has a hydrogen atom will dissociate to give you innercity parochial all right and so it turns out it is only this hydrogen that come off and once this kind comes so we call the acidic acid and he wanted to to use the generic
29:09
formula this would be a test when the time comes now it Is that so it's gonna form an iron like that and we call this the acetate the accident and iron were ascertained I am and so this would be be in the form Amy Klein all right so this is a weak acid and this week as it has only 1 proton that could come off when the proton comes all the forms yesterday and I are right and so on this is what the structure looks like now I wonder why the quandary for this then I'm going to say the city gasses so this is a formula city gasses when it's placed in water or would undergo dissociation of ionization to give me I join you mind plus the acetate all right and if I write the case like this I know it is 1 . 7 6 times 10 the negative vibes most beleaguered and writing the case right next to that equilibrium is a reminder to you because now you have an idea of what that it could be a mistress and look like right to know we a weak acid so let's say once again that we start with . 1 more of the week gasses so you might have an initial concentration and let's say I have .period ones you may have 0 observed that the costs were not concerned about the concentration of water rights so this is what I stop now I'm going to look at the change and so on it's 0 1 2 1 2 1 state geometries sell here excess consumed the number another lost plus and therefore at the and I know this will be . 1 minus that this is the best that's right not like strong acids where X is going to be really large this is a weak acid so waterway about that discovery was small because a lot of it's going to remain under reactor state so I can say that now 88 it is 1 . 7 6 times tend the negative 5 miles per liter equals by writing a lot less actually equilibrium expression that we had to my times he acetate and island divided by acidic gasses right which gives me times status divided by 2 . 1 minus that's a writer which is exquisite oval . 1 minus X now he wanted to do all this equation in another quarter of the equation in this or that .period ready to question and you should find out what exit but remember that cake agent to fight so if is really small we know that this is the ideal place to apply work the approximation because we know it is going to with was market case attended mainly by that X is relatively small arrived so to keep the medicine simple ball I can make a smart approximation I saying my approximation is because it's a weak acid I can say . 1 minus X will approximated . 1 in other words X this so small compared to point 1 molar weekend neglected OK so we made the approximations announcement had yet to be quite simple to now knowledge save 1 . 7 times 10 1 . 7 million we write that 1 . 7 6 times stands by holes per liter equals X squared over . 1 right so I approximation and multiply this by that entered the square root and I can't figure out where exit and so on if you out of value for that last fall over the answer comes out to be 1 . 3 times tend negative 3 Moeller OK so now narrow and ask you what was next I have go all right because remember anybody can make approximations you have to go back and make sure the approximation is indeed valid however validated my approximations of the next step is invalidated approximations and that is the amount that I have which is a guess what was my approximation excess small compared to 1 . 1 so that the don't say this is small compared to 1 molar times 100 and that comes out to 1 . 3 per cent notice that fall below my threshold yes remember we just big enough to number and we lose the use by and as a threshold and this pop fall well below the 5 per cent threshold right and so we know all this approximation is valid none of this approximation is valid now I can calculate standard Association or was sent the composition or Percent ionization anyone leaving only the same thing and what does that mean per cent decomposition is where the amount that decomposed or the amount that I know what is the man that I analyze it Dexter never see that so it's X divided by the initial concentrations of this would be best divided by the initial concentration times 100 which is 1 . 3 times since 3 Moeller divided by 1 molar times 100 which Disney 1 . 3 per cent the same calculation of bit of Dallas as well so what does that tell me it's a strong acid year 100 molecules of acid there was strong acid all 100 molecules and Associates all right hearing after noticing a gasses without that telling me that him 100 molecules only 1 out of every 100 associates we see that there's a big difference it's either all of it associates completely I told him that the small number all right in this case by every mall 100 molecules of the acid in water only 1 the associate and because it produces every 100 molecules produces only 1 I dream I now this is a weak acid all right and therefore we call it a week gas now about 1 calculates so we now that the majority my concentration the quarterbacks which equals 1 . 3 times Clinton ended 3 smaller the survival of the hard during my concentration is the 1st then I can calculate the pH of the solution appeared to be negative log of that and appeared comes out to be 2 . 8 9 so the peertopeer solution is that and certainly not the pH now you should be able to calculate he awaits can you do that at home I think you know that teaches you can capital would appeal wages which is subtract 40 International at the height during my concentration is you know what the hydroxyl concentrations exactly and of every problem should be able to go from 1 to the other all right so that the accused 2 . 8 9 that industry is sitting right so it isn't talking about the hydroxyl concentrations that look right because I don't intend hydroxide should equal 1 times 10 to the 14th all right so this is an example although we guess it so once again you go back to the table this table this out we gasses arrived and once again and these are board where you start with the ones that
38:33
have the highest paid to the ones that have the lowest so you look at anything that has K ALS than what will act as a weak acid singular decayed values you can see it started like tend to negative 1 and goes all the way down to we hear this is now the fact that the yellow line in the sand Hi during a mine water conjugate as stared at the bottom of the year in waters of the assets and now looking at the continent is Aceves here with each Georgia Walker and hydroxide is Bates became a value is 1 times 10 Canadian teams alright so anything that falls between take it 1 and the tendinitis 14 will act as a weak acid in water Oregon solvent is once now if we got memories are already in terms of K value so strong acids and the top and you keep going down the acids get weaker and weaker and weaker and weaker alright so anything that falls in this range will be a weak acid saying that as a K value in this range will act as a weak acid water are and these are ranked in terms of relative cities and so even tho the result we ask that you can say that this acid this asset is a stronger acids and that's so we're looking at me gasses but between the weak gasses you can see that 1 acid is stronger than the other so you're asked to do rank acids in terms of relative strength how strongly acid water rank acids in terms of relative strengths that you have decayed values all you have to do is look at the case values and rank them so you can rent them from strong acids to weak acids that even within the weak acids you can see that he will be able gasses 1 will be as strong a weak acid and the other to understand that and so we can rank in terms of relative stressed however that once you hit the water as the acid not to look at this as as methanol the direct methanol decay of methanol incidents the negative 18 so can you see that we're renting in these in terms of relative acid strands so methanol cannot act as a possible while because guess what while is a strong acid during Senate water if you place methanol in water but then all contact as acid because what exactly is the acid because water is as strong as the middle you get so you look at a morning at the bottom if you please ammonia and water you can't ammonia can act as an acid in water because water is a strong acid so what it is that kind of colorcoded and minutes said and that's in red letters as strong acid you water it highlighted in black will act as a weak acid water but these last 2 actually highlighted see the colors here but these are and who and what you should keep in mind is that those substances can act as an acid in water because water turns out to be a strong acids if you put them in the water water that disaster did not issue offer examples are in because water is a stronger acid so keep that in mind so during a lot because is this onetime stand naked for again now we said that if you take the negative log of K and you end up with people he dealt with PKK right sometimes very often instead of listing of became values very often the Peking values of listed are right to you need to know how to read acids based on PK values especially by students there and even look at a minor last and you know the different types of minor molasses and you will look at team the values of the minor acids that when the city hydrogen will come off and you can rank these minor assets based on the PGA values and say you know which is a strong acid and so on all right and so do rank those that you have and what we listed under thinking about because once again why do we take the widely always look at a lot of experience because you can see that the range of numbers of various started with something like 10 to the power level and going to tend to the negative 14 15 so the range of numbers and enormous and so it's a lot easier for us to comprehend the scale you can compress it to a smaller scale and so that's what we turned to a logarithmic scale but you take the PGA remembered what was a lot of the here and now becomes a negative numbers here all right so you can see that in the PKK is scale something that has a big lead take a number will be a strong asset all right and has the name number gets smaller and smaller it's going to get the relative strength of the Athens the decree and so now when PGA equals 0 that would be Wente is 1 and so any down less than 0 and 14 will be weak gasoline but you see the pedia value actually gets bigger and bigger and bigger as the acid gets weaker and weaker and weaker results were jointly mind is that is still kind of looked around arriving in large negative numbers are strong right Chewalla numbers a stronger and stronger and then the numbers are weaker right until you get the pickier 14 when you figure 14 you know that anything that has a been about 14 will not act as acid water because water will be stronger acids and so the place company water it's the water that act as an acid and not that of a substance that and so water is what will produce the during my right and so and keep that in mind as well so print this out I don't expect you to memorize these values but on the exam I will expect you you to be able to rank relative acids and bases are right stability acid and I give you a series of accidents here when he's in terms of relative absence trends were expected to be able to do is not memorized as well expected able to do it having this had the with you the will to rank them based on the handouts the cable and sometimes I the leader of the key in values ruling DPP so you should be able to write guesses based on complicated sometimes on the obligation to adjudicate values you should be able to use scaled to rank relative acid based on their ass extracts are right and the other that I want to remind you of this scale you can see that if you take strong acids they're actually very few examples of strong acids in fact this list lists out almost all the known strong acids missing like 1 or 2 so it is not if you look at a formula but it is not something that falls within those then the chances are that that substance action actors in the cast that it's because you look at the wealth of substances out there there's more examples will be gasses compared to strong acids all right and so it is a formula that you haven't seen before it's not on this list it's most likely is a weak acid rain and strong can so so we look that assets we look at strong acids we looked at gasses you know how it happened the heat of a strong acid you know how to count the pH of the weak acid arise because a weak acid you actually have to to write the gloom expression you're making approximation Soffer X and the data government Maryland sending the bases so there is a direct analogy just as it looked that asses now we can look at bases so we we look at basis so there is a direct parallel that runs between acids and bases and so we were looking at races we can say and it cost solution it is said it contains an excess of hydroxide irons over 100 mines right and so we know
47:58
in other words what that means is that hydroxide Island is a greater amount than her junior minds and that's what that solution is basically a right just like acid bases can be strong bases for really the basis of gave same will and so on "quotation mark would have strong bases and fighting a strong once again and we can say then strong bases now only human assets the confidence that we deal with is acid dissociation constant came when we deal with bases what is a constant that deal with the association constant which is key so this inherent in strongly says KB is greater than 1 right 2 Strong Mason the associated or finalized completely an almost 100 per cent writer and so an example of a strong base and give you 2 examples of a strong base 1 strong base the image to
49:38
minus right and another strong base would be on India architects that says so the 2 examples of astronomy is and was stopped
49:53
after today the next time will take the same examples and figure out how to figure out the hydroxide and conservation of based on that the only each time that you might suppose that there