Chapter 16: Acid / Base Equilibrium - introduction

Ajouté : 2026-05-21

[00:00:03]my folks we're gonna start chapter 17 acids and bases I'm on slide number two we're first gonna define what an acid is and what a base is a bronsted acid is a substance that donates a proton donates an H+ we call that a proton you know because a hydrogen atom looks like this with a proton and electron if it loses that electron and all that's left is the proton and that's this would be a hydrogen atom right and so that's H+ so acids are things that donate protons bases those are going to be substances that accept a proton and if you look on the slide it says bronsted acid and bronsted base this just named after the scientist who first kind of postulated this idea that that this is what can constitute an acid or base a proton donor which is an acid or a proton acceptor which is a base okay let's go to slide number three you might remember in the past we talked about strong electrolytes and weak electrolytes that idea is going to apply to acids and bases so a strong electrolyte remember that's a substance like sodium chloride that when it dissolves in water you can you know we can write NaCl aqueous remember this means dissolves in water but what really happens when sodium chloride dissolves in water is it completely breaks into individual sodium ions and individual chloride ions and because this is what happens when sodium chloride dissolves in water that it completely dissociates we say that is a strong electrolyte it completely dissociates into ions when it's dissolved a weak electrolyte on the other hand is something that does not completely dissociate that would be like acetic acid when it dissolves this would be liquid actually I should write it like this the liquid dissolves in water you know if you put it in water it becomes engquist and then this reversibly dissociates that should be aqueous here into protons and the acetate anion so because of this fact that acetic acid when it dissolves only partially associates it's a weak electrolyte so strong electrolytes completely dissociate when dissolved in water like sodium chloride weak electrolytes they only partially dissociate when they are dissolved in water now this idea of strong and weak electrolyte that can be applied to acids and bases so it's just like this if the things an acid but it's also a strong electrolyte then we call it a strong acid if it things an acid and it's also a weak electrolyte such as acetic acid then we call it a weak acid so let's go over some examples of this and I'm still on slide number three so a strong acid that's gonna be an acid that is also a strong electrolyte so some examples of this are hydrochloric acid if I dissolve some hydrochloric acid into water none of it exists like this all of it dissociates into H+ ions and dissolve chloride ions same thing with hbr hydrobromic acid when this gets dissolved in water and none of it stays as hydrogen excuse me hydrogen bromide dissolved molecules they all dissociate into hydrogen ions and bromide ions same thing with look at this each no.3 I wonder what that does well you know I've been doing chemistry for 20-25 years and so when I see this I immediately recognize the nitrate ion if you were unable to quickly identify the nitrate ion in this particular substance then you should go back and here I'm gonna say it memorize your polyatomic ions it's helpful to go back and look over these when we're doing stuff in acids and bases all right knowing your polyatomic ions knowing what their structures are and what their charges are is really going to be useful as we go through the acid base chapter and we're going to be covering acids and bases for a while so get back to these get back to them okay anyway so nitric acid is a strong acid so that means it's going to donate a proton and it's going to completely dissociate and I indicate see there's the nitrate ion I indicate this complete dissociation with an arrow that goes one way you can think of this as not existing in sort of like a reversible fashion for the most part this thing goes in one direction you put that in water and boom it dissociates now if you look on the slide slide number three also see that h2so4 first proton only is listed as a strong acid well what the heck does that mean well this is what it means if I take some sulfuric acid and dissolve it in water I'm gonna get H+ and the hydrogen sulfate ion and every molecule of this that gets dissolved it dissociates into H+ and hso4 but hey look this hydrogen sulfate this can also act as an acid but this particular case it reacts reversibly so some of this actually exists in solution you know some of it dissociates into H+ that's my kids upstairs oh and sulfate teaching at home okay so the hydrogen sulfate partially dissociates into H+ and sulfate and so what we would say is that this particular substance it's an acid because it donates H+ but it's going to be a weak acid and this appears it's gonna be a strong acid so you're not gonna find any of this dissolved in water any of this gets in water boom it goes to an H+ and an hso4 it goes to a proton and a hydrogen sulfate and then some of this that's formed some of it remains like this so you can actually find some of this existing in solution floating around in there if you can see you know ions which we can but anyway some of this though it's it's also an acid but it dissociates partially so it there's a reversible process going on here that that hits an equilibrium value okay that's the end of slide 3 let's move on to slide number 4 we're going to apply this same idea to assets and basis so a strong base like sodium hydroxide let's see what is that gonna do well if it's a solid I'm gonna put it in water and it's going to dissolve so I can write this but none of the sodium hydroxide that has dissolved in the water exists as the unit sodium hydroxide all of it dissociates into sodium ions and hydroxide ions and because of that because of brightness one way arrow we don't get any of this in the water we get all this because of that sodium hydroxide is considered to be a strong base by the way we define the base is something that accepts a proton which is true this is another clue that you have a base that base is something that's going to generate hydroxide when it's dissolved in water so that's another way we can identify bases now there's the weak base ammonia nh3 it's a gas and when it gets dissolved in water like this see this would represent the gaseous ammonia you can tell that you ever make out some ammonia at home go find it in the bathroom sink and open that up be careful don't sniff it too too much because some of the dissolved ammonia in the water it escapes as a gas and boy that's a pungent odor but anyway if you take your household ammonia which has dissolved ammonia in it some of it well let me write this this way hold on I screwed up Timon is tricky some of the ammonia that's dissolved in water will react with the water in a reversible fashion to form the ammonium ion and the hydroxide ion so because when ammonia gets into water it generates hydroxide ion this is characteristic of a base but it does so in a reversible fashion there's not a one way over here is that there's a you know it goes in both directions what's a base because the generation of Oh h- but it's going to be a weak one because there's some of this hanging out in your strong base there's none of the original base hanging out in in the solution all of that goes to free hydroxide we'll stop here