dude i'm so sorry dude i'm sorry it took me so long to get this video out i know like the first ap chem exam is coming on may 7th so i know this is kind of late i'm sorry but i've been really busy okay so i finally made the time to do it these videos take a really long time to make but i'm doing it okay i'm sorry we are finally going to finish a b cam better late than never am i right that is my motto okay hello everybody i'm cara and today we are going to be talking about acids and bases unit 8 okay we're only two units away from finishing the whole a b chem chat like the whole a b chemistry course and the reason i didn't finish eight and nine beforehand is because like last year they didn't they just took out these units because of like covet and that kind of thing and i really didn't get the time to get back into a b cam because i'm not studying for ap chem like i mean it's been a really long time since i've been in ap camp and the like prep for these videos take a really really long time so i really haven't gone around to it but now we're going to talk about all this cool stuff intro to after the babies phpoh all that cool stuff you guys love all that stuff i know you guys do but because you guys have left such nice comments on all the other videos you guys were begging me for more and a ton of you guys watched my crash card that's why i'm making these videos okay so thank you guys but enough talking let's get into the good stuff let's do it all right so the first thing we're going to talk about is what are acids and bases and basically the most basic definition of an acid and basically come up with this dude called arrhenius okay he was actually friends or something i don't even know how to say even a french accent i'm not even going to try dude but basically this is what people learn when they think about acids and bases right like acids are the dudes who give off each plus ions and basically these h plus ions are called hydrogen ions they might also be called protons whatever but basically acids give off these guys right you probably know this already but that's the most basic definition of an acid then bases they give off guess what that's right o h minus okay and these ions are called hydroxide right like hydrogen and oxygen so makes sense makes sense okay and that's basically it we're done with the unit we know what acids their bases are let's go no i'm kidding but this is very important make sure you know the arrhenius definition it's just the most basic one another thing to note is that h plus ions you probably have heard that like they turn into h3o plus ions and that like these are basically the same thing they're basically the same thing okay so honestly i would not worry too much about a30 plus but doesn't know that it exists okay and it's called a hydronium ion but essentially you could use a plus and h3o plus like interchangeably and i always use h so like who cares about this dude this guy sucks okay okay so basically now that we know what arrhenius acid and bases are we could talk about neutralization reactions and you probably could guess that neutralization means that the acid and the base you put them together you don't get a pineapple pen you get a not after base right it cancels out so essentially if we have like acl which is hydrochloric acid plus naoh we could think about it this way right like essentially the h you get like h plus c l minus n a plus and o h minus how could we rearrange this to make something nice that's right we basically have the o h minus and the eighth plus come together to get h2o and then we get nacl right so essentially you can see we started with an acid and a base right but then we ended up with water and a salt so that's basically the definition of a neutralization reaction right like you have an arrhenius base that gives off an h plus the h plus uh combines with the oh minus given by the arrhenius base and that gives you water and then the remaining stuff does form the salt and basically all the salted is just a combination of ions right and na plus cl minus are on so that's how why it's called the salt acid this is the base this is water and that's the salt now something cool that not many people realize is if you do the net ionic equation all neutralization reactors have the same net ionic equation so let us just do it out i kind of had it before but we could do like h plus plus cl minus plus any any plus plus oh h minus and then we go to h2o right because it's liquid it doesn't dissociate right there's a liquid and the aqueous right because it's dissolved in water plus n a plus plus cl minus we cancel out the n a plus the cl minus and we get h plus plus oh h minus yields h2o and this is really what it is for every single neutralization reaction they're not a single neutralization reaction that did not have this equation and it makes sense right the ace plus is an acid the o h minus is a hydroxide on and then they combine to form water right h plus neutralizes with o h minus that's why it's called a neutralization reaction okay so now we basically have an idea of what an acid is what a base is and what happens if you react them now we could talk about what ph is right and you guys probably know that ph is like a measure of how acidic or basic something is right like you probably had it ingrained in your head that peach less than seven means acidic right ph equal to seven is equal to neutral and ph is greater than seven is basic so now let us take this thing that you probably know and like combine it with the molecular part of it okay so literally the way i like to think about it is like you got a p you got an h right and the p could probably be like percent or something like something to do with like the concentration of h so essentially from that you could tell that the definition is ph is equal to negative log of the concentration of h plus now this equation kind of looks scary i mean hopefully it doesn't look scary in just a couple lines but like still it's kind of annoying so let us just do a couple examples and hopefully it will be more clear so essentially let us say that your concentration of h plus ions which is basically the moles of h plus over the total like volume of the solution in liters right because you know that like um concentration is in moles per liter then essentially if it was 10 to the negative 5 right we would take the log 10 of this which gives us a negative 5 and then we take the negative of that so that means that this is ph 5. so essentially the way you could just think about it if you're taking you just ignore the 10 you look at the thing and you take the negative of it because like p just supposed to be positive right so basically that that's how you do it just snatch that exponent and make it positive and you got the ph okay another example right like let's just say we have like h plus is like i don't know ten to the negative nine i don't know so you take the exponent you make it a positive you get ph is equal to like nine okay then what happens if we don't have a nice power of ten that is a question well then we have like two to the negative nine or something i don't know no what about like two times ten to the negative nine so that it is in scientific notation and now you might be expecting what is the cool trick that kara's gonna show us now that's right i'm not gonna show you a cool trick just kidding i'm gonna show you the coolest trick in the book okay use a calculator that's right bruh so essentially you just plug in the formula like it's not that complicated 2 times 10 to the negative 9. and you get 8.70 so let us put that in okay so what do we see about the trend here right so essentially as your hydrogen ion concentration is getting lost right like 10 to the negative 5 is way bigger than 10 to the negative 9 right your ph is going up right even though your like concentration of like hydrogen is going down your ph goes up so it's basically the opposite and this makes sense right like acids have more hydrogen ions but they have the lowest ph so essentially that's why there's a negative here because when you go down hydrogen ion concentration you want to actually go up in ph and that also makes sense between these two right like we're going from 10 to the negative nine we're doubling the amount of hydrogen ions right and that's why it is slightly less ph right because you have more hydrogen ions more acidic means less ph okay so now we have this epic equation for ph ph is equal to the negative log of h plus you guys better know this is very important but then there is also poh right and what do you expect right it's literally like the same thing as ph except now you got o-h so instead of putting an h-plus we put uh o-h-minus very epic stuff okay so the one thing you got to know about ph and poh is that they sum to 14. and how do you remember this the way i remember it is because like peach the middle is seven right so like probably at the middle you got poh and ph are the same right so seven and seven so the thumb to fourteen right if someone's a midpoint right like you probably had a thumb 14 and it like goes between 0 and 14. so we got 14. so essentially in order to do this unit well you have to be very comfortable between flipping between all of these things right because you basically use ph a ton you use like you might be given the hydrogen ion concentration and you need to be able to find all these numbers so let's just do a couple examples it's not too complicated but basically you take your 10 to the negative five right we take this we get the positive of the exponent to get our ph is equal to five right there's hydrogen ion concentration now essentially we can find poh just using the equation and now these are the only three equations you're ever gonna have to know for like poh and ph right so essentially if you have five you could do poh gives you nine right 14 minus five and then basically you plug it in here right so essentially if to get from h plus to ph you take the exponent and negative negate it then for this one you negate it and put it at the exponent right so essentially our o h minus is going to be take this put it negative 9 and then we put a 10 there and we are good all right very nice so now we know what ph is we know what poh is very cool stuff so now let's do a little bit more of a practical like example because usually ap chem is mean and they decide not to give you like the actual like hydrogen ion concentration right off the bat so we got to do a couple more amine examples right so let us say let us say that we have 2.0 moles of h2so4 right in like i don't know 1.5 liters of water right sulfuric acid is a very strong acid so we don't have to worry about any like weak acid nonsense we'll talk about that later but this is a strong acid so essentially what a strong acid does is it spits out all its h pluses so essentially because of the two here we call it diprotic okay right two die die means two so that's why it's diprotic guess what like i don't know hno3 would be called what is one in greek testing your latin roots knowledge let's go well essentially this is just going to be mono product right mono means one so that's why it's called monoprotic but we don't care about latin okay latin is kind of irrelevant bruh but like what we actually care about is what it means right so essentially if there are two hydrogens that means that for every h2so4 molecule you're actually going to get two of them dude it's like a two for one special it's kind of epic so essentially when we put this acid in the water it actually becomes 4.0 moles of hydrogen right because essentially we start with like two moles of h2so4 right and then this goes into two h2 plus a so4 two minus right so essentially if you have 2.0 here and all of them could get converted here then essentially you had to take one time you had to multiply by two right so now we have 4.0 moles of hydrogen like hydrogen on it i don't know how the two there that's wrong okay luckily let's just make this a little bit bigger because we need a smaller number to make this nice so let's just do like i don't know um like oh let's say like 10 liters 10 liters of water okay so essentially we have four moles of hydrogen ions in 10 liters of water and remember we're trying to look for hydrogen ion concentration okay we don't want the number of moles we want the moles per liter okay so essentially whenever you're doing this you have to make sure you get two moles per liter so essentially we have 4.0 moles we just divide by liters to get 4.0 moles per liters over 10. so we want moles per liter we just take our moles and we divide by liters makes sense over 10 liters and we get the 0.4 uh molarity right and now if we want to find the ph of the solution all we got to do is plug it into our epic equation negative log of hydrogen ion concentration which is equal to negative log of 0.4 which is equal to let's see now what i like to do before i actually like do the calculation is just check what you think it might be right so essentially this is between 1 and 0.1 right we have to go by power of the 10 and 0.1 is 10 to the negative 1. so essentially the ph should be between zero and one okay let us check if we actually get something between zero and one and then we should be good so we do negative log of zero point four we'll start on 0.4 and get 0.4 again i did not expect that but you can see right like it's between 0 and 1 we were able to predict it very nice we get our ph is equal to 0.4 no why don't we do it for something a bit harder like a base right so essentially let's say we have like 0.1 like moles of naoh in i don't know let's say like two liters of water okay so you can see there's only one oh in this molecule so we don't have to worry about multiplying by two or anything fancy like that so we can just chill and we know that there is going to be 0.1 moles of oh minus after it breaks apart in the water okay so now we want to find the concentration right we don't like moles okay no one likes moles naked mole rats are disgusting okay so we actually had to find molarity okay and the way we do that it'll be divided by two liters to get 0.05 moles per liter okay and now we have our concentration of o h minus and remember our three equations right we had ph poh and we had our 14 and this is equal to negative log of h plus negative log of oh minus and is equal to ph plus poh okay so which one of these equations has an o h minus in it that is right we got this one over here so this is the one we're going to use we want to take a negative log of this and that is equal to negative log of 0.05 let us find that out negative log of 0.05 and we get 1.3 okay and now we have poh right so now we could use this equation we've already used this one so we don't want to use it again right we basically just look at the only other one we've used right the only one the only the only thing we know are poh and oh and the only one that remains that has poh is this one so that's what we use next right so we do 14 minus 1.3 and we get 12.7 so now we have ph let's go we got our answer ph is equal to 12.7 as expected it's in a basic solution so it will obviously have greater than 7ph dude that's like another thing to check okay if you're putting an acid there's no way you're going to get more than 7ph i'm sorry to break it to you but you can't go basic after adding like gobs of acid okay yeah i made that mistake more than once but we don't talk about that we don't talk about that okay now another question that you might get based on this like all this stuff is based on just that basic poh and ph equations right like those three equations those are all you got to know to solve all kinds of problems right so here's another one that you can actually solve using those equations so let's say that we have like 100 milliliters of i don't know let's say ph like three solution right and we add 900 milliliters of distilled water and let's just say we want to find the ph of the final solution right so essentially how do we find ph we want to know the hydrogen ion concentration and how do we get the hydrogen ion concentration if the liters are changing right like my concentration is moles over liters and liters are changing so how do we like find the actual ph now essentially like you know what the final like volume of the container is right like eventually it's just going to end up with one liter of solution right 100 milliliters plus 900 milliliters is equal to 1 liter but in order to find ph we actually had to know the hydrogen ion concentration and essentially when we add in distilled water we're not adding in like many like h plus ions relative to this right so essentially we just need to find the initial number of h plus signs that's not going to change and then we could divide it by the total volume right we want moles over liters so let's calculate the original number of like moles of hydrogen ions right so ph3 remember we take the negative and we put it like to the power of 10 right so 10 to the negative 3 is our h plus ion concentration then essentially the moles per liter in the initial solution right in this part but we want to find the moles right because we want to find moles over liters so let's find the moles by multiplying by 100 milliliters which is like 0.1 liters and essentially we get that we have like um we have 10 to the negative 4 moles of hydrogen ions right so essentially we divide by 1 liter we get 10 to the negative 4 moles per liter and we take the negative of the exponent to get ph is equal to four hooray we did it boys very nice okay because one definition of bases is not kind of fun enough okay we gotta have a little bit more fun with our definitions of bases we're now gonna talk about a new definition for acids and bases because arrhenius is one was kind of troll it doesn't cover all cases so let's talk about a different type bronsted lowry okay the way i like to remember this is arrhenius is like one name kind of boring you know kind of simple that's why it's the most basic but then braum said larry that is such a cool name okay that's two names in fact two is always greater than one okay so that's why this is a little bit more sophisticated and that's why we're talking about a second so acids are considered exactly the same as arrhenius theory so i guess not that sophisticated so these guys basically give off these h plus ions all right make sense right we don't have to worry too much about it nothing too fancy here but then so when you get to the bases it's kind of scary bases are not ones that give off o h minus ones they're actually things that snatch h plus one now this kind of makes sense right like if acids do one thing you would probably expect bases to do the opposite it kind of makes sense like even what in arrhenius definition when you give off o-h minus those guys go and eat up all the h pluses so basically same thing all right so why don't we look at what happens when we react a bronsted-lowry acid with a bronsted-lowry base and these are called acid-base reactions so if we have nh3 plus hcl that yields nh4 plus plus cl minus i think so let me ask you a very epic question what is this guy is this guy an acid a base or a troll i don't know what they're often for about indian acid or base come on you guys got to tell me bro why nobody answering this is so sad i thought cameras could talk but the answer is actually it is a base even though it has like three hydrogens no one cares okay the only thing we care about is what it actually does and you can see that it goes from an nh3 to an nh4 plus so clearly it grabbed an h plus it went and snatched it from the cl minus the cl minus is all alone and scared now but clearly this guy is a base because he is snatching an h plus from the cl minus but essentially if this guy is a base then this guy has to be an acid right because essentially like this guy is giving off or this guy is grabbing an h plus then if we went the other way this guy would have to give off an h plus so in fact this is called the conjugate acid and this is called a conjugate base so essentially once you have these bronsted-lowry acids and bases they basically have conjugate pairs and all that means that like they're on opposite sides of the reaction one has the hydrogen and one doesn't have the hydrogen and the one with the hydrogen is the acid makes sense the reason why the one with the hydrogen is the acid is because acids give off h flux that's the one thing you got to know acids give off h plus and that's why this guy is going to be the conjugate acid this guy's going to be the conjugate base now what's cool about water the water is kind of a troll and like i know i kind of added that option in at the joke but water is actually neither okay it's neither an acid or a base right like for example if you react nh3 with like water it essentially becomes like nh4 plus plus oh minus and essentially in this case the water is actually acting as an acid right it's giving off its h plus and becoming an o h minus so in this case water is acting as an acid right but what happens if we have like i don't know what happens that we had like hcl plus h2o yields like um cl minus plus h3o plus so in this case the water is actually gaining a proton right so in this case it's acting at the base so water is something called amphoteric and like this is kind of a useless term i don't think they'll care too much about it but amfo means like both like amphibian is like both line and water that's why amphoteric means that it's both acid and the base makes sense honestly like water the only thing that's acid in a base because literally it's h and o h minus like it's really made of the two things combined so it kind of makes sense that it's both an acid and a base all right so now we got to talk about the difference between strong acids and strong bases and weak acids and weak bases so we saw like with h2so4 that's an example of a strong acid we saw that two moles of sulfuric acid went in and we know immediately the four moles of h both are going to go out right like every single one of those hydrogen atoms gets like expelled like these atoms do not like their hydrogens at all a weak acid on the other hand like hc2 um h3o2 very fun trivia question what is this boy that's right acetic acid this guy's a weak acid right like if you put in one mole of acetic acid you actually don't get one mole of hydrogen ions like separated from the acetic acid some of the acetic acid will stay together with its hydrogen because it loves it so much and only a little bit will actually end up like coming out into the solution and that makes sense right a stronger acid should give off more hydrogen right so essentially all the strong acids give off their hydrogen fully there's none left of the original acid so let's just give a couple more examples of strong and weak acids so it's pretty important to remember these right because on the test they're not going to tell you whether it's strong or weak right they're only going to tell you here's the acid find the ph of the solution so h2 has a fourth one hno3 is one like hclo4 is one hclo3 is also one and essentially there's also pickle hibber high that's what my like chemistry teacher taught me i think it works perfectly but hickle hibber and hot and these are all strong and then essentially all the other ones are gonna be weak dude my chemistry teacher gave me the best ways to remember this in the universe basically if there are two more oxygens and hydrogens it's probably going to be a strong acid now i don't know how true this is but i've used that rule like as a guideline for everything and it worked perfectly okay like there's probably some exception to the rule but like in all the examples that come up on a b chem test as long as you just have like two more oxygens and hydrogen it is for sure a strong acid like you see right three and one that's for sure two more you got four and one that is three more holy moly that is crazy you got three in one that has two more so these are all strong and then you just got your tickle hipper height didn't know you're forgetting that dude pickles you were high holy moly that's such a good such a good mnemonic holy a couple more examples of weak acids but like as long as you know the strong acids you should be good right you could probably say that oh it's not a strong acid so it's probably weak there's like hf there's nh4 plus there's a couple more but honestly you don't have to worry about it too much okay just remember the strong acid then you're good now let us talk about bases right so eventually for this one we kind of need a periodic table so let me get that up dude ptl.com is the best okay you got to use ptable.com if you don't use ptable.com that's just kind of sad but essentially um bases paired with like these kind of guys right so essentially like for example na you got naoh li you got lioh and then because like we got ca which is two plus that's why it's cao h2 right so essentially just visually all of these guys are strong bases and then like these three guys are strong bases so essentially there's like the b over here and that's how you find all the strong bases all right so these are all the strong bases that you had to know just remember that it showed up as a b over here that's all you got to know some weak bases you got like nh3 that's like the only example i know but like basically if it's not a strong base it's probably going to be a weak beat now i don't know how relevant this is honestly but basically you could kind of predict how acidic things are going to be so let's just explain how to predict it just in case like you guys want to know and so you guys could probably derive some of these yourself but essentially like let's just look at like hf and hcl so hf is a weak acid right but acl is a very strong one so what is the difference well essentially fluorine is way smaller right so it's basically grabbing really really tight onto that hydrogen and we know that acids are the ones that let their hydrogens go right like really strong acids just let all their hydrogens go they don't get like they don't care but then the weak acids they hold on to their h plus right so essentially the reason why they're not as strong is because they don't release as much h plus as their strong counterparts and that makes sense right if chlorine is smaller then it's gonna keep its hydrogen and chlorine bigger so it's actually going to be like more likely to give off its hydrogen and if you look at like hbr and hi hpr is actually stronger of an acid than hcl because hbr is even bigger right so it's even more likely to give off with the h like h plus ion and then h i is literally the strongest one out of all these because it has like a really really big iodine atom that's just like i don't care about any of you guys just see you later see you later i don't care so essentially bigger atom slash less hoggy equals a better acid very very important stuff okay and also you can think about it this way like the hf bond is really really strong right it's like the it has higher bond energy and like as your bond energy decreases like you're more likely to give off the h plus right because it's really easy to break that bond so this has the highest bond energy and the lowest okay moving on let us talk about the next thing okay so so far we've only been talking about how to do calculations related to like strong acids and strong bases let us talk about like weak stuff now and the first thing we got to talk about is water itself so water itself is kind of like a very weak acid base kind of thing right like water actually dissociates into h plus and oh minus right so it's like kind of both so essentially we kind of think about this as an equilibrium kind of thing so essentially like there's a liquid this is aqueous this aqueous and how do you find equilibrium coefficients right like the constant you basically just take the aqueous ones right you multiply them together the product side first and you divide by the aqueous stuff on the left side but there's no aqueous stuff on the left side because water is liquid so essentially this is the like this is what the equilibrium constant of this reaction is and technically i should probably put a double arrow because it's going both ways but essentially this is the equilibrium constant for water okay and it's called kw now does anybody have a guess does anybody have a guess what is what kw is equal to at standard temperature hint hint we got ph plus poh is equal to 14. what do you guys think so essentially like you know that like if you have a h plus ion concentration of 10 to the negative 5 then your ph is going to be 5 right which means that your poh is going to be 9 which means that your hoh minus concentration is going to be equal to 10 to the negative 9 right what happens if your h plus ion concentration is like i don't know 10 to the negative seven right neutral then your pg is seven your poh of seven and then your o h minus is also going to be 10 to the negative seven so what is your equilibrium constant that is right you can see that no matter what like what you do no matter what your h plus ion concentration is it always multiplies to 10 to the negative 14. so essentially this like the like this value for the equilibrium constant is actually what proves this equation so essentially they calculated like okay we're gonna have like this equilibrium and a bunch of different like h plus and oh minus concentrations and then they found that it was 10 to the negative 14 which is why you have ph plus poh is equal to 14. now why is this relevant the reason why it's relevant is because this is only true at 25 degrees celsius right the definition of neutral like in neutral we usually think of as like ph is equal to seven but actually what it means is that h plus and oh minus concentrations are equal which at like 25 degrees celsius is one ph is equal to seven but what happens if our kw actually became like 10 to the negative 13. then in that case neutral ph would actually be 6.5 right so essentially like the ph of neutral could change but as long as you have an equal number of hydrogen and like hydroxide ions that's when you have neutrality so the key takeaway from this thing is that like neutrality is o h minus the concentration is equal to each plus right and that's and then like same thing for acidic and basic o h minus is greater than h plus for basic dudes now this is pretty logical right it makes sense but just keep in mind that they might try to troll you and if they say like kw is not equal to 10 to the negative 14 then you might actually have to use this definition right this definition works all the time so i would just recommend using this definition like it's pretty straightforward when ph 7 is neutral but like to use this definition is a lot like it worked every single time okay so that was with water why did we do this epic equilibrium strat with like i don't know let's just do with an acid or something so for a weak acid we basically got like h a where a is just some random atom yields like h plus plus a minus right like it's essentially giving off an h plus now we know for a strong acid there's no equilibrium here right like all of it is just going this way no one cares it's not going to take back its h plus it doesn't care anymore but for a weak acid it's actually going both ways right like some of it wants to keep holding on to their h plus some of it wants us to give it away the aqueous and this is aqueous all of these are aqueous so essentially we could write our k of the acid is equal to h plus times a minus over h right we're just taking the product of the aqueous stuff on the right side and dividing it by the aqueous stuff on the left side and we get an epic equation right so now the reason why this is useful is you can actually use this to say how strong an asset is right like the bigger this like value is that means that more hydrogen atoms relative to how many like of the initial atom there is right like if there's more h plus relative to the acid that means there's a stronger acid right so essentially we could use the ka of an acid to determine how strong it is and then also like you could just do pka right like p you could just think of as taking the negative log right that's what you do for oh that's what you do with for h plus so if you want to do pka you take negative log of the k8 all right so this ka is called the acid dissociation constant right it's how much of the acid act we end up dissociating the more it is the more acid associates the less it is the less the acid dissociates okay so before we get into an example of how to use that equation let us talk about the base side of it right so essentially we have like i don't know we have aoh yields a plus o h minus a plus plus oh h minus and we could write our equation kb the base dissociation constant is equal to a plus plus oh minus times oh minus over aoa and then pka is the same pkb is the same thing so it is going to be like negative log of kb okay pretty straightforward let us use it to determine some ph's so let us say that we have a 0.5 molar solution of like i don't know hno2 which is nitrous acid and this is a weak acid right there's only one more oxygen than hydrogen and we need two more hot oxygen and hydrogen for it to be a strong acid and the ka for nitrous acid is equal to four times ten to the negative four okay so essentially like in my previous like equilibrium video i completely forgot to talk about ice chart but now we can actually use ice charts and i will explain how they work but like honestly being i don't really like ice charts and i'll tell you why but let's just get into it okay so if we write out the equation we basically have hno2 yields h plus plus no2 minus okay now essentially what an ice chart does is it basically takes your initial concentration right you start with 0.5 moles of molar molarity of nitrous acid and you start with zero of the other stuff right now the change is actually different right so like s moles of this guy you have to add estimates of each of these right because for each one of these that is consumed it makes one of each of the other ones right so essentially if we do minus s here we have to do plus s over here and over here so then we basically get that our equilibrium state is going to have 0.5 minus f s and s and essentially at equilibrium the that like quotient we had the like uh no2 minus times h plus over h no2 this has to equal our ka at the equilibrium right that's the definition of the equilibrium constant so essentially we could plug in right we could plug in our values right we have our initial we have our change we have our equilibrium concentrations right so at equilibrium we want s times s over 0.5 minus f to equal 4 times 10 to the negative 4. now like there's two ways to solve this basically like if if s is tiny relative to 0.5 we don't really care like what exactly it is right so essentially we just need to solve for s and c whether it's close and if it's not close then we could just assume that we ignored this part okay so if we solve for it we basically get like s squared over 0.5 is equal to 4 times 10 to the negative 4. so that means s squared is equal to 2 times 10 to the negative 4. let us solve for f square root of 2 times 10 to the negative 4. okay so 0.01 is like visually like tiny compared to 0.5 right the technical rule is like five percent rule or something as long as it's five percent of the original you're good and you can see that it is only three percent of the original so we don't we could actually ignore it so so essentially our s is just equal to 0.014 so if our s is 0.014 that is equal like our s is also the like hydrogen ion concentration the h plus is no2 minus right so our s is also the concentration of h plus ions right so essentially we could use the concentration if we got concentration we know how to find ph we just take the negative log of it negative log of 0.014 so then we can take negative log of 0.014 and we get like 1.85 at our p 1.85 ph and we are done very nice okay why don't we do an example with a base two just to get it get it real good say we have 1.0 molar uh solution of ammonia which have a kb of 1.8 times 10 to the negative 5 okay so essentially our equation is nh3 eos or nh3 plus h2o yields nh4 plus plus hoh minus right so essentially this is the same thing as saying our well if we draw our ice chart now the reason why i don't like the icd chart basically is because like it kind of just like makes you not understand what you're doing right like you can just think about it this way right you start with 1.0 and if you consume s we just like say s is how much actually goes through the reaction right that means there's s less here and there is s more of the thing we want right like s more of both of these like i know the same thing with the ice chart but you just understand what it's doing so you don't actually have to write out the ice chart every single time so essentially s of it is going through the reaction which means that s of it is getting consumed and s of each of the products are getting produced makes sense okay so essentially we could say that s squared over 1.0 minus f is equal to 1.8 times 10 to the negative 5. so if we assume that s is negligible we could solve for f squared and we get of 1.8 times 10 to the negative 5 is 0.004 0.00 or s is equal to 0.00424 and now if we just want to find the ph remember that s is actually the o h minus concentration so if we want to find the poh we would take like the um negative log of this and we get 2.37 now remember we're do the base okay so we're not done yet remember to check your answers like if it's if you're getting like a tiny ph for a base you got something wrong okay so essentially we know this athlete should be the poh so we just do 14 minus that and we get 11.6 that are ph nice okay ph is equal to 11.6 all right very cool sorry i didn't explain this part very well but like but basically you just want the reaction quotient right nh4 plus times oh minus over nh3 to equal your equilibrium constant right because that's the definition of the equilibrium constant this should equal the equilibrium constant at equilibrium okay so now one more thing we got to talk about before we talk about buffers are something called salts right and i've kind of touched on it before but it's basically two ions getting put together but songs could themselves be acids or bases so the one thing that really helped me when understanding salt is that like when you have a conjugate acid and base right let's say the acid is pretty strong that basically means that the base is really weak so essentially conjugate acid and bases are opposite of each other right so if the acid is kind of strong then the base is really weak if the conjugate base is kind of strong then the acid is really weak so take for example like the salt c2h3o2 um like na right so when you're trying to decide whether this is acidic or basic what you want to do is you want to first break it up into the ions and figure out what they come from right this is acetic acid like this is the acetate ion and that comes from acetic acid right so hc2 h3o2 and then this guy comes from naoh right so this guy is the conjugate acid of naoh and naoh is really really strong right so essentially this guy is going to be a very weak acid very very weak acid i should probably put a very very in all caps there we go now i know that this guy is a weak acid which means that like this guy is also going to be pretty weak but like still stronger than a very very weak acid right so this guy's going to be a weak um weak base but it's still stronger than this one right because this is a very strong acid which means that this is a very weak acid but this is only a weak base so that that basically means that overall this ion or this salt is going to be absolutely basic because this one came from a weak acid this one came from a strong base but now we're taking the conjugates right so essentially it gets flipped and that's why we now have a basic thing so just to give you guys a couple more examples right like we basically could have f and or naf right so once again we have something from a weak acid and something from a weak base but because it's conjugate we flip it right like because this comes from a strong base you would expect this whole thing to be basic right but essentially it's a conjugate of that so we actually have to take opposite which is why this is actually acidic another example is like nh4 cl right hcl is a very strong acid right and this comes from a pretty weak base so essentially like you would think it would be acidic because cl comes from a strong acid but it is a conjugate remember we're flipping it around so now this actually is basic so like basically whenever you're thinking about it just look at which one it comes from a strong thing and then it's just the opposite of that right like this one comes from a strong acid which is why it's basic this one comes from a strong base which is why it's acidic now both of them come from strong acids like it's just neutral right it doesn't do anything and if like both of them come from weak then you can't really tell right because like they're different levels of weakness so let me just break it down for you guys comes from and then dotted up strong acid it's actually basic right because retaining the conjugate if it comes from a strong base weak acid it's actually acidic it comes from strong acid and strong base then it's neutral because both of them are going to be really really weak and if it comes from a weak acid and weak base then it's going to be you don't have enough information to tell necessarily but like if they ask you for it just say neutral but like you don't technically don't have enough information okay so just remember this this is all you got to know for salt okay and now finally we get to talk about buffers okay very fun dude these ones suck so bad i i could barely remember how all this stuff worked but basically buffers are what they sound like right essentially they're active buffers to ph changes so when you add a really strong acid it actually won't change as much if there's a buffer inside so that's kind of cool basically the way it works is like let's just say we have a hc2 h3o2 and c2h3o2na so essentially like this guy wants to dissociate into h plus and c2h3o2 but this guy already has to dissociate into c2h3o2 right because it's like an ionic compound it automatically dissociates so when you look at the equilibrium right h2 c2h3o2 gives you h plus and c2h3o2 minus to the equilibrium basically this guy is going to push the equilibrium left right because you're adding more of this now like more of this guy wants to get formed right whenever you push up one side it wants to even it out so essentially now you have like this big reservoir of acid right and essentially if you were to add a base the equilibrium would shift this way right and essentially you can make more h plus on demand because you have a bunch of these guys right or for example let's just say you added in a acid right then essentially the acid would push the equilibrium more this way and like the actual h plus ion concentration won't change that much because it's getting eaten up by the acetic acid so essentially no matter what you do you're not going to change the ph by that much because this equilibrium will just shift in different directions and essentially that's created by having like the acid itself and a salt that gives you something called the common ion effect right you basically want to match this ion and this ion and then it makes the equilibrium stable common ion effect all that means is that when you add a common ion it'll shift the equilibrium back this way and that actually allows it to act as a buffer so just an example of the common ion effect let's just say we have one mole of like h3 cooh and one mole of ch3coona okay now essentially this guy has a ka of 1.8 times 10 to the negative five and basically we could think about it this way right so essentially we know we start with like this many um moles of ch3co right so we start with one mole of this guy right and let's just say that s moles undergo the reaction right so we have a reaction ch3 cooh yields h plus plus ch3coo minus right so if s moles undergo it we're basically consuming one like s of the moles of the one mole originally we're at like creating s moles of h plus and we are adding more moles of this so on right s more mole than that so essentially if we want our um if we want our quotient to equal our equilibrium constant right we have h plus times ch3 and this should equal to this at equilibrium so essentially we could say that s times one plus f over one minus f is equal to one point eight times ten to the negative five okay so essentially like we could basically ignore these right because they're basically going to be tiny compared to the ones right so essentially we just get that s is equal to 1.8 times 10 to the negative five in which case this is also going to be the like um this is also going to be the concentration of the hydrogen ions right so now we can just find the ph as the negative log of that hey very nice we get 4.74 hey very good okay all right nice we did it boys very nice okay so now so now i'm just going to introduce one last thing we could talk about and basically that is the henderson hasselbalch equation i kind of budgeted that bruh pretend i know how to talk okay pretend i know how to talk and basically this just takes the equation that we wrote and it makes it a lot simpler okay so instead of how to use ice charts you could just use this and you're basically done so essentially we could derive this equation by saying that ka is equal to h plus times a minus where a minus is the conjugate base over h a right now essentially if we take the log of this right we basically get that p k a is equal to log of um h a over a minus plus or sorry minus log of h plus and we know what log of h plus is right that's just going to be like ph so essentially we get pka which is plus log of h a over a minus is equal to uh ph right we just bring this over to that side so basically we get that pka plus log of a minus over h equal to ph and that over here is a henderson hasselbalch equation so essentially what we could have done last time instead of like going through the whole ice chart is going to put in our pka and then we would put our a minus and a which were both one molarity right so this would just be log one which is equal to zero so essentially we would just get the pka is equal to ph very nice in our previous example and then like obviously that makes sense right we just took negative log of 1.8 times 10 to the negative 5 that's why it worked out so nicely interestingly enough this is called the half equivalence point that's basically when your a minus and aj plus are the same all right so now the last thing we got to do is talk about titration right now essentially for a strong acid and strong base this is pretty easy right because essentially what you're going to do is you're just going to keep adding base like let's just say you're trying to figure out the concentration of a strong acid right all you got to do is you got to add a base that you know the concentration of until the ph becomes seven and then once you have that then like all you got to do is you just like do some equations and figure it out right so let's just say we wanted to figure out like the concentration of hcl and we have like i don't know 0.1 molar naoh right and let's just say we had um let's say we had 200 milliliters of this right so essentially if it takes 200 milliliters of naoh in order to um like neutralize this then essentially the amount of h plus must have exactly cancels out with the number of o h minus right so basically when you're doing titrations you basically want mole of h plus to equal mole of ohm and the mole of this let's just say we ended up using 200 milliliters right then essentially moles of naoh is equal to 0.1 times 0.2 right you got moles per liter you multiply by 0.2 liters okay and then we know the moles of hydrogen here is equal to 200 milliliters or 0.2 liters times the concentration of hcl right which is what we're trying to solve for so essentially we just get that the concentration of hcl is equal to 0.1 molar okay that's an m that is an m what happens if for example this was h2so4 right then in this case we would have to take 0.2 liters and the concentration of h2so4 right but each concentration like each mole of h2o4 turns into two h2 ions right so you have to actually multiply by two and you basically want um and then this one stays the same right you basically have 0.2 times 0.1 and you get that your concentration of h2so4 is equal to 0.05 noise okay so titration of strong acid strong weight is pretty easy right you just want to balance out the h plus and the oh on both sides and then you're done for a weak acid with a strong base it's kind of hard actually weak acid strong base for a strong acid strong base your curve kind of looks like this right because essentially like originally it's mostly the acid and then once you get to the base it'll just go like that right once you get more of the base it'll start going opposite direction okay but for a weak acid strong base it actually looks something like this so over here like the weak acid actually acts like a buffer which is why it actually starts going pretty strongly and then it starts like leveling off because the athlete is becoming a buffer so let's talk about how to deal with that so let's just say we have like i don't know 0.5 molar like hno2 right which have a ka of 4 times 10 to the negative 4. and we are adding in like i don't know 0.05 moles of naoh right so essentially what the naoh does is it completely like converts some of this um like hno2 in to its conjugate um base right so essentially um 0.5 so let's just say there's like one liter of this right then essentially we start with 0.5 moles of hno2 right then when it reacts with 0.05 moles of naoh then it becomes 0.45 moles of hno2 and 0.05 moles of no2 minus right so essentially now we can actually apply henderson hasselbach right because we have a uh we have an acid we have its conjugate base and we could say pka plus log of 0.05 over 0.45 is equal to ph and we just calculate this negative log of um 4 times 10 to the negative 4 plus um log of 0.05 over 0.45 and hooray we get a ph of 2.44 like essentially you could see how this changed it right like if we only if we had like 0.05 moles of naoh without the buffer then essentially we would have a concentration of 0.05 negative logs of 0.05 we would have got a ph of 1.3 so essentially this buffer is basically changing the um it's preventing the ph from going too hot or sorry yeah yeah oh no wait what no it would it was like 14 minus this okay yeah so basically you would have like such a high ph if it was not for this buffer okay so you basically get the idea right so um the one thing you want to remember when you're doing weak acid plus a strong base is that you like when the strong base is added it converts some of the acid to its conjugate base right and then you could apply henderson hasselbach basically at the beginning you use hendelston has to hasselback but once your strong base converts all the weak acid to its conjugate base then you can just like ignore the weak acid right because now it's all the strong base and then you can just do it at a normal titration okay well i hope that was helpful i'm kind of rusty at ap cam so i'm sorry that was not the most coherent explanation possible i'm sorry but i hope it was helpful thank you guys so much for watching as always if you enjoyed the video leave a like and subscribe for more thank you guys for watching again comment down below what else you guys want to see but other than that i'm done so thank you guys for watching again and see you guys next time good luck on the [Music] app [Music] you