all right I want to throw everybody totally off today everybody write down the word Titans everybody write down the word Titans TI T ANS all right I hope everybody's written down the word Titans now the subject of today's lecture is the behavior of different substances in an aquous environment before we can discuss about specific substances we want to talk real quickly about what has to happen in order for something to conduct electricity to conduct electricity a substance has to have charged particles and those charged particles have to be capable of movement they can't be fixed in place there is a category of compounds known as electrolytes and electrolytes are any substance that when dissolved in water conduct electricity an electrolyte are is any substance that when dissolved in water conducts electricity you need to write that down if you're not doing so already all right so an electrolyte is any substance that when dissolved in water conducts electricity well what's an example of an electrolyte once again I'm going to trot out my favorite go example there of sodium chloride now if you just have regular old boring sodium chloride solid and you place a electrical wire in it you're not going to get any conduction why because sodium chloride even though it consists of sodium ions and chloride ions are charged particles those charged particles are locked in place in a crystal we talked about ionic compounds existing in Crystal those charge particles inside a crystal can't move they're being held in place by forces of attraction and they can't move well when we place them in water an interesting thing happens water is what's known as a polar molecule meaning it has has a partial meaning has a positive end and a negative end it has a bent shape so it's kind of like a boomerang here and our oxygen has a partial negative charge and the two high and the hydrogen tail here has a partial positive charge water is so highly po polar that these partial negative and partial positive charges are just too attractive for the sodium and the chloride to resist I mean let's face it sodium and chloride they've been together since the beginning you know small town not a large pool to date kind of an attraction of convenience they hit the water and all of a sudden all these water molecules are running around with partial negative and partial positive charges how can these ions resist so when you place sodium chloride in water the attraction of the sodium ions the attraction of the sodium ions for the partial negative charge on a water molecule and the attraction of the chloride ion for the partial positive charge on a water molecule causes the sodium chloride to break up you place sodium chloride in water and instead of being that strong Crystal you get a mix of ions now floating around and associating with water molecules so when you play sodium chloride and water it breaks up into sodium and into chloride now you have sodium and chloride ions they're charged particles correct they got a positive charge negative charge so now you have charged particles and they're capable movement instead of being locked in place in this Crystal they're dancing out around among the water molecules they've entered the great disco Tech of life so when you place an ionic compound in water it breaks up into ions since sodium chloride produces charge particles capable of movement when placed in water that means sodium chloride is an electrolyte sodium chloride is also our representative ionic compound right whenever we need to talk about a ionic compound I always wound up talk I always wind up talking about sodium chloride well all soluble ionic compounds are going to behave exactly like sodium chloride n s t i t u e n t soluble ionic compounds break up into their constituent ions in water in other words when you place sodium and chloride in water it breaks up into the sodium ion and the chloride ion you need to be able to write the solubility equation for an ionic compound dissolving in water all right write the equation for what happens when sodium sulfate is placed in water so we have sodium sulfate and we're placing it in water what happens couple steps are required to do this and I always recommend that you follow these steps to avoid making simple Mistakes by now you're well versed in your n clature rules so step one you're going to use your nomenclature rule to identify the ions you know that this compound is sodium sulfate that means it's made of two ions the sodium ion and the sulfate ion the sodium ion you know from your periodic table sodium's in group 1 a so it has a so it forms an ion of + one sulfate you've memorized is S so4 2 negative identify the ions the reason I tell you to identify the ions is people want to make up ions for some reason when they look at this if you look at it you've got two sodium ions for every one sulfate ion right for some reason people want to invent a polyatomic ion they want to say uh I've got that as one of my ions no have we ever learned about a a binary sodium ion no we haven't right don't go inventing ions or inventing new rules sodium and an ionic compound exists as a monatomic ion however you do have two of them okay so step one identify your ions step two write them as products so I've got sodium and now it's in water so it's aquous and I have sulfate and it's in water so it's aquous and notice they are existing as ions now they've broken up they're not attracted to each other so they charges hanging out there and exposed so we actually have to write that charge I didn't just write sodium sodium ion I didn't just write sulfate I write sulfate with a charge showing also that's an AQ there right phases are going to become very important in this chapter phases are almost the point of the entire chapter so make sure you recognize that these are aquous so when I place sodium sulfate in water it breaks up into sodium and breaks up into sulfate now we do have one last thing to do and that's step three to balance if we look I have two sodiums over here so I'm going to need two sodiums over there I don't want to invent polyatomic ions so I'm not going to change my numbers down here instead I'm going to had a coefficient just like I was balancing a normal chemical equation all right so that's how you write what happens when an ionic compounds placed in water let's do one more real quickly all right another example I strongly recommend pausing me and trying this on your own all right hopefully you're back from having worked it on your own we've got magnesium chloride and I'm dissolving it in water notice I should have point out last time I'm writing my water here above the arrow to show what's happening but water is not actually participating in the reaction yes but to indicate that I've placed my substance in water I'm writing water right here above the arrow all right so step one identify those air ions well I have magnesium chloride so one of my ions is going to be magnesium magnesium is in group 2 a so it's positive2 then I have chloride chlorides in group 7A and it's cl1 and I think chloride is perhaps the most commonly gotten wrong ion right it's cl1 even though there's a two there there's no cl2 two negative ion right that does not exist matter of fact I'm embarrassed I wrote it I don't want it going into the wrong wrong into your your minds there right your Ion is CL negative we will take care of that subscript on the flip side all right so now I step two I write them as the products we've got magnesium 2+ aquous and then we've got the chloride ion aquous got my charges showing now step three I do my balancing I have one magnesium here so I need one magnesium here I have two chlorines here so I need two chlorides over there and that's that chemistry is easy life is hard all right let's look at an example of a problem the type of which if you have lab you'll be actually solving in the experimental setting a one molar solution of which of the following would be the best conductor well remember in order to conduct something you have to have charged particles capable of movement the more particles the better conductor so the question really can be thought of is which of these three substances produces the most particles when placed in water well for every one mole of potassium nitrate I place in water I get two moles of particles out for every one Mo of potassium sulfate I place in water I get two potassium ions and one sulfate ion so for every 1 mole of pottassium sulfide I place in water I wind up with 3 moles of particles but wait what about our iron 3 nitrate for every one mole of iron 3 nitrate I place in water I wind up with one iron 3 ion and three nitrate ions or four moles of particles so even though I may have only one mole of the starting product there's a multiplying effect when you place it in water for every one mole of this I wind up with four moles of particles so even though I'm starting with the same amount of each one of these compounds the number of particles is radically different making this a much better conductor at four particles per mole than this and that's the sort of thing you'll be addressing directly in lab another common category of electrolytes are acids acids can also be electrolytes but we'll talk more about them later let's talk about something that's not an electrolyte the opposite of an electrolyte is a non-electrolyte a non-electrolyte is a substance that does not conduct electricities when placed in water for example something that gets placed in water quite frequently ethanol you take liquid ethanol you place it in water and all you get is ethanol that's wet the water molecules don't pull the atoms of ethanol apart notice that we've switched categories of compound we see carbon and hydrogen there are no Metals ethanol is a calent compound calent compounds generally unless they're an acid or a base Cove valent compound unless they are an acid or a base are non electrolytes but because they don't come apart in water they just get wet we're not going to spend a lot of time talking about them let's move on all right now we want to introduce a couple new terms strong electrolytes and weak electrolytes strong electrolytes disassociate completely in water weak electrolytes only partially disassociate in water let's tackle them one at a time a strong electrolyte disassociates completely in water once again a great example of a strong electrolytes table salt you place table salt in water if you start with 100 formula units of table salt and you place it in water then you'll end up with zero formula units of sodium chloride and 100 sodium ions and 100 chloride ions in other words their splits vills their reaction go goes to completion the dissolving of the ionic marriage is complete There's No Going Back the reaction goes to completion for a strong electrolyte most ionic compounds are strong electrolytes so most ionic compounds are strong electrolytes another category of strong electrolytes are strong acids just a second here all right a strong acid well first of all I don't think we've ever met acids at all so we should probably pause and Define acids all right before we Define an acid it's been way too long since we've defined um since we've defined a word for you to write down just like it's been a really long time since the Browns have anything resembling a franchise quarterback so why don't you write down the Browns write down the Browns all right we have to Define an acid an acid is any substance that increases the hydrogen ion content of water the classic example of an acid is hydrochloric acid you place hydrochloric acid in water and just like an ionic compound it separates into two parts one of these two parts is a hydrogen ion now the problem is we have a hydrogen ion floating free in water well remember our shape of our water molecule our water molecule is bent but as a bent shape derived from a tetrahedral so we have these two hydrogen swept back in One Direction and then we've got two lone pairs of electrons sticking out in the other direction these two lone pairs of electrons are pure unadulterated negative charge and you've got a hydrogen ion which is a proton pure unadulterated positive charge I got to tell you these two forces find each other irresistible so irresistible that in an aquous solution this hydrogen ion never actually exists it is instantly bonded to water forming a coordinate coent bond with one of those lone pairs of electrons to form h3o Plus or the hydronium ion therefore you'll often see the definition of an ACI acid somewhat modified you'll often see the definition of an acid given as so an acid is anything that increases the hydronium ion content of water why because you'll never actually see a hydrogen ion floating free therefore how we write acid reactions needs to change to reflect this new definition all right so you have an acid hydrochloric acid first thing I should point out to you is how do you know you have an acid an acid will have hydrogen as the first element so we see hydrogen there is the first element so that's a clue we have an acid now we place this acid in water now instead of just writing that hydrogen ion when the breakup occurs we're now going to reflect what actually happens in water and we're going to say it forms the hydronium ion and the chloride ion and some of you are saying wait a second Dr Kelly wait a second wait just a minute here after all don't we have to have this equation balanced it looks like we added a bunch of hydrogen and a bunch of oxygen no we didn't right we have water written above our Arrow it's functioning as a reactant over here however it's not something we really want to focus on in our reaction so even though we're including it our balance by having hydronium occur over here we're minimizing its importance by writing it over the arrow because the main star of our reaction is our acid as it dissociates to hydro dronium and chloride so that's the reason for that unusual notation that you see here but an acid is anything that increases the hydronium ion content of water let's take a look at another example another classic example of an acid is nitric acid once again I see my first element is hydrogen so I have an acid I place my acid in water and I wind up with hydronium and then I wind up with the rest of the acid minus the hydronium ion remember it's a hydrogen ion leaving which means that whatever is left over is going to develop a negative charge so you're removing the hydrogen ion that hydrogen is leaving behind its electron so we have our nitric acid going to the hydronium ion and going to nitric acid so that's our acid disassociation reaction not a strong acid is an acid that dissociates completely in water you're responsible for knowing your strong acids your strong acids are perchloric acid nitric acid sulfuric acid then your halogenic acids Hydrochloric hydrob bromic and hydroiodic note hydrochloric acid is not on this list it is not a strong acid these are your six strong acids you responsible for this point on now till the end of your existence for knowing that these are your six strong acids all of these acids disassociate completely when placed in water meaning if I have let's set up a chart here meaning if I start with 100 molecules of nitric acid then at the end of my reaction I'm going to have zero molecules of nitric acid left 100 hydronium ions and 100 nitrate ions and you're probably saying well why this big deal that's the way we've always assumed chemical reactions occur in reality a lot of chemical reactions don't occur to completion instead a lot of chemical reactions occur until they reach a state of what is known as equilibrium weak acids are examples of such reactions a weak acid is one that does not disassociate completely in water an example of a weak acid is hydrochloric hydrochloric acid when placed in water does disassociate and form the hydronium ion and the fluoride ion but only kind of first of all notice I've written my arrow a funny looking way I've got a big Arrow a big half Arrow going this direction and a smaller half Arrow going that direction what do we mean when we say hydrochloric acid doesn't disassociate completely if I start off with 100 molecules of hydrochloric acid at the end of my reaction I'll have 80 molecules of hydrochloric acid 20 hydronium ions and 20 fluoride ions in other words instead of 100% of my molecules breaking up only 20% will but wait there's more using the term end is really inappropriate when it comes to a weak acid because weak acids are the ultimate drama couple everybody went to high school with this this couple couple right they're together one moment they're broken up the next moment they're together the day before Valentine's Day they're broken up on Valentine's Day they're back together the day after Valentine's Day they're broken up two days later right think about any sitcom couple right Robin and Ted Robin and Barney Ross and Rachel they're together one moment they're broken up the next moment they can't make up their mind that's how weak acids are so when we say that our reaction ends it doesn't really end it reaches what's known as equilibrium and at equilibrium the acids that are the rate of acids breaking up equals the rates of acids reforming in other words weak acids reach a state where the number of acid molecules breaking up is equal to the number of acid molecules reforming so our weak acids are we have molecules of weak acids that are constantly breaking up and constantly reforming in other words we have a reaction that's a two-way street not only that but they're always occurring hydrochloric acid molecules are always breaking up and new ones are always forming however this breakup cycle This Together cycle eventually reaches a state where the ratio of molecules broken up to molecules together is constant for example here we have 20 broken up to 80 together or a 1/4 ratio the weak acid will reach a state where that ratio of one broken up to every four together is constant the breakups are still occurring and the togethers are still occurr occurring but the ratio doesn't change when you reach that state where the ratio is unchanged that State's referred to as equilibrium I would say a good 50% of what we will do in 180 deals with this concept of equilibrium so if you don't understand it fully now don't sweat it we're going to spend lot of time on it next semester here's the bottom line that you need to get from this one you need to be comfortable with the fact that for a weak acid if you start with 100 only some of them are going to break up and at equilibrium you'll have 80 together and 20 broken up so when you have a weak acid you have less than complete breaking up a strong acid you have 100% breaking up weak acid you only have partially broken up things that gives us two new terms and Cycles us back to where we started today I told you we'd get back there speaking of things that always seem to get back there how is it that the Jaguars always seem to cycle back to the top of the draft I mean really it's the highlight of their season uh you think they'd be good at it by now but apparently not why don't you write down Jaguars write down Jaguars j a g u a r s Jaguars it it occurred to me real quickly I never told you what your weak acids are any acid that is not one of the six straw acids is a weak acid any acid that is not one of the six and that's a six there six strong acids is a weak acid okay so a strong electrolyte is an electrolyte that disassociates completely in water most soluble ionic compounds and strong acids are strong electrolytes weak electrolytes are electrolytes that do not disassociate completely in water weak acids are an example of a weak electrolyte all right a polyprotic acid oh by the way this falls under the category of St we didn't have anywhere else to place it in the book so we're slapping it on here a polyprotic acid is an acid that has more than one acidic hydrogen to lose the classic example of a polyprotic acid is carbonic acid carbonic acid has two hydrogens is capable of losing the question that you need to ask yourself and you need to ask yourself as a chemist is does the carbonic acid molecule lose both hydrogens at once or does it only lose one at a time the gut reaction is to say well it's got two hydrogens that want to leave it so both are going to leave turns out that that is totally wrong both hydrogens won't leave the carbonate here's why let's think about the effects of removing that first hydrogen we have carbonic acid we place it in our water and some of the molecules disassociate to form the hydronium ion and the bicarbonate ion so we've removed one of our protons the second proton is going to have to leave the bicarbonate ion if the carbon if carbonic acid is going to lose both of those protons we're asking a hydrogen with a positive charge to leave a compound with a negative charge right once that first proton leaves up here we're left with a bicarbonate ion which has a negative charge this hydrogen wants to leave with a positive charge do you think something with a positive charge wants to leave something with a negative charge no it's going to be much harder for it to leave there are other factors that play into the inability of this hydrogen to leave but those are subjects for another day what you need to realize is that when you have a polyprotic acid such as carbonic acid if you start off with 100 molecules of carbonic acid that first reaction will have at the end of it 80 of them staying together 20 of them breaking up of the 20 molecules that break up those 20 bicarbonate ions are the start of another acid reaction of those 20 that you start with uh maybe one will break up or maybe two will break up so what you see is that even though our carbonic acid has two hydrogens to lose only the first one will be lost to any great extent a much smaller portion of that second hydrogens will leave the acid most of the time a polyprotic acid is only going to lose one hydrogen some of the molecules will lose an additional hydrogen but very very few right we started off our little conversation here with 100 molecules of carbonic acid and then we wound up with only two of them losing both hydrogens right so when you have a polyprotic acid only the first Hydrogen leaves to an appreciable degree now there are exceptions to this um sulfuric acid being a notable exceptions where both those Hy where both one hydrogen leaves completely and the second one leaves in great numbers but um for the most part only that first Hydrogen leaves to an appreciable degree if you have lab you'll discuss the um ramifications for this for conducting by performing an experiment in other words yes you're listening to this for your pre-lab lecture but I'm not going to tell you what those U ra ifications are ah what am I kidding you let's go ahead and do it a 0.1 molar solution of which of the following would be a better conductor let's deal with a simple one first calcium bromide is an ionic compound and since it's an ionic compound we know that in the presence of water is going to break up and remember don't invent polyatomic ions is going to form three ions right it's going to produce three particles for every one particle we of calcium bromide we put in our gut reaction is to say hey Dr Kelly we have carbonic acid up here so we should get three particles out wrong that's not what happens remember carbonic acid is a weak acid so first it doesn't lose all its hydrogens at once it only loses one at a time that second hydrogen basically doesn't leave at all and because it's a weak acid if I put 100 molecules of this in only 20 of them may break up so I only may get 20 charged particles as opposed to my calcium bromide where if I put in 100 molecules of it I get 100 of these and 200 of these so our conducting solution is going to be much stronger with calcium bromide than our weak acid and you'll see experimental evidence of it in the laboratory that's it for this lab um just like um the draft concludes when the baron make the last pick so why doesn't everybody write down Broncos b r o n c o s Broncos