Buffers

本站添加: 2026-05-11

[00:00:00]foreign and I'm gonna introduce you to buffers um buffers you've probably had experience with these are things that happen around you they're even buffer systems that occur within your body but you may not be familiar with what they actually are so buffers are solutions that resist a change in PH when hydrogen or hydroxide is added so they're going to resist a change in PH whenever an acid or a base is added to the solution there are two most common types of buffers that we deal with one is where we have a weak acid and it's conjugate based salt because the acid can react with the any base that is added and the conjugate base can react with any acid that is added then we also have a weak base and it's conjugate acid salt and yet again we have one substance that can react if an acid is added and we have one substance that can react if a base is added so here's kind of what we have so here would be a buffer um we have the weak acid of acetic acid the vinegar on the left and then we have the sodium acetate on the right so we have acetic acid is our acid the acetate ion is its conjugate base ion So that's its conjugate-based salt so we have these negative acetate ions that could react with hydrogen ions that are added from an acid and then we also have the acetic acid that could react with hydroxide if it is added same kind of thing occurs if we have a base buffer so here we have ammonia and then we have ammonium chloride mixed together so ammonia remember can absorb hydrogens acting as a bronston-lowry base so it can react with hydrogens we also have ammonium that can give up hydrogens to react with hydroxide if a base is added so actually looking at these reactions that occur so if we have a nitrous acid sodium nitrite buffer so that means that we have nitrous acid which is hno2 and sodium nitrite is going to have that nitrite ion which is the NO2 negative what happens is if we add an acid the acid gets consumed by the basic part of the buffer which is the nitrite ion so if we add some form of acid so acid tends to have the h3o plus the hydronium if that is added to our base our nitrite ion what happens is the acid gives up its hydrogen to make water and the base the nitrite ion accepts that hydrogen to make is parent acid the nitrous acid now what happens if we add a base to this is the base is going to get consumed by the acid so remember a base produces that hydroxide ion if that reacts with our acid our nitrous acid our acid gives up a hydrogen to react with the hydroxide which makes water and leaves behind that nitrite ion one thing that you will notice is in both cases for a buffer it will always produce water in some way shape or form whatever it is neutralizing whatever added acid or base we have all right so looking at what's happening more on the particulate level and here we have a buffer solution so notice that we have the parent acid and then the anion kind of floating around if we add an acid so we add hydrogen ions to it the hydrogens react with those anions producing more of the acid but yet again it's able to consume that acid whereas if the buffer solution we then add hydroxide hydroxide is going to react with hydrogens so it's going to take hydrogens from those acids and produce water leaving behind more of the anion more of the conjugate base so here's yet again kind of what happens looking at the particulate level so generally with a buffer we have equal amounts of the acid in its conjugate base whenever we add an acid this is the one on the on the left we have more of the acid and less of the anion the conjugate base so pH would go down but only a little bit only slightly whereas looking at the kind of graph on the right if we added the base the hydroxide that's going to produce more of the anions and less of the parent acid so less of the acid means that the pH should go up but yet again only slightly all right let's look at another buffer so if we have the ammonia ammonium chloride buffer solution so ammonia is in H3 ammonium chloride is NH 4 CL but it's the nh4 Plus is our conjugate acid for our ammonium and yet again if we add an acid it has to get consumed by the base if we add acid the h3o Plus add that to our base the ammonia the acid the h3o plus gives up a hydrogen making water and that hydrogen can't just float around by itself so it will attach onto the ammonia to make that ammonium ion and the flip side is true if we add a base that gets consumed by the acid so adding a base remember is adding hydroxide our acid our conjugate acid is the ammonium ion hydroxide will react with a hydrogen to make water leaving behind that ammonia base so those are our typical more common acid-base problems that we see or excuse me buffer problems that we see so we said for something to be considered a buffer it is any solution that contains something that can consume hydrogen ions so something with basic properties that can consume hydrogen and something that can consume hydroxide ions is something that is acidic it has to have both it all if it only has one it is not a buffer so it has to have something that can absorb hydrogen and hydroxide to be considered a buffer so we need to look at and what other ways could a buffer system exist because like we said those two are the most common but that is not anything so we said that for something to be a buffer we can have our weak assonance conjugate base we can also have the weak base and its conjugate acid another thing that we can look at is we can also have an amphoteric ion so remember amphoteric means it can be an acid or a base so it can act both ways so it can either gain a hydrogen or lose a hydrogen um some things that are amphoteric that we looked at we've talked about water before but some of our amphoteric ions would be something like the hydrogen carbonate ion or dihydrogen phosphate ion those could easily lose or gaining hydrogen the other one that we can use is if we have a salt without spectators so that means that both ions are going to produce an acid or a base so whenever we looked at our salts and we were trying to determine if they were acidic or basic remember we had those ones that we were able to cancel out because they would produce like a strong s or strong base we want things that cannot cancel that cannot produce those spectators so an example here would be ammonium night right because if you look at our salts whenever we did these earlier ammonium can produce ammonia whereas the nitrite can produce the nitrous acid both of those excuse me that should be it to you both of those are weak acids or bases so that neither one will cancel so this one solution in itself can act as a buffer um all right so here are just other examples of the four types of buffers we said we come across so we have the weak acid and it's conjugate base salt so like hydrofluoric acid and sodium fluoride our acids the hydrofluoric acid the fluoride ion can be our base ion our conjugate base so notice that this can react with the hydrogen and hydroxide overall same thing for the weak base and it's conjugate acid salt we did that same reaction earlier um the salt without spectator here we use the ammonium fluoride because ammonium can become ammonia the fluoride ion can become hydrofluoric acid which is a weak acid so both of those will react and then we have the salt that has that amphoteric ion so here we have sodium hydrogen carbonate and hydrogen carbonate can either gain a hydrogen or lose a hydrogen so that ion by itself can act as acidic or basic and in our next video we're actually going to start doing calculations with buffers and looking at if we add a certain amount of acid or a certain amount of Base how does that affect the pH overall