all right chem 115 um fall 2020 um september 28 monday lecture okay um at the end of friday's lecture we talked about uh solubility rules solubility rules is a set of generalized rules um as a tool for us to determine whether a ionic compound is soluble or insoluble when you're dealing with solution chemistry problems okay and we talk about two rules already and number one and number two these two are the two soluble rules okay now the ions mentioned in this these two rules okay all together there should be uh six positive ions and six and six negative ions positive ions are the group one a metal cation so lithium sodium potassium rubidium and cesium okay and ammonium okay these six positive ions okay no matter what kind of negative ion they're combined together with okay you see these one of these guys as your positive ion for your compound even if the negative ion is something that you've never seen before you can take it for granted that this ionic compound that you have is a soluble ionic compound which means when it's in a solution chemical problem some solution chemical reaction that compound should fully dissociate 100 into three ions okay and rule number two is very similar in the only difference is we're dealing with six negative ions okay and there are nitrate ions nitrate ions nitride ions um chloric chloride ions per chloric perchlorate ions acetate ions and bicarbonate ions okay so if you see a chemical compound let's say i see something like this okay manganese nitrate and i don't have a rule discussing manganese this is a transition metal i don't understand i don't know the solubility of manganese ions but it doesn't matter you see your nitrate ion right there you know this compound is a soluble ionic compound and if it's in a solution chemical reaction this thing would fully break down into manganese ion and two nitrate okay how do i know that manganese here has a two plus charge well nitrate has negative one charge and you have two of them in the formula manganese got to be plus two to offset and make the chemical compound neutral all right so you see these 12 ions 6 positive 6 negative the compound involved is always a strong electrolyte a soluble salt okay now number three okay chloride ion bromide ion and iodide ion compounds okay are soluble except when combined with three positive ions and there's silver lead two plus and mercury 1 iron okay so number 3 is still kind of a soluble rule but this is a soluble rule with exception now these first two are soluble rules no exception you see these guys then you can put your stamp on soluble okay no matter what the other positive or negative ion is now for chloride bromide and iodide okay mostly they make soluble ionic compounds so majority of the compound that you see containing ionic compound containing chloride ion containing bromide ion containing iodide ion okay would be put into the strong electrolyte soluble salt category okay the only exception happens with for those three ions are these three positive ions okay so three positive ions three negative ions how many possible combinations do you have well three times three nine combinations okay so what do you mean here you're i'm telling you that silver chloride silver bromide silver iodide lead chloride lead bromide lead iodide mercury one chloride mercury one bromide and mercury one iodide or insoluble okay if these guys shows up on the product product side of a chemical reaction solution chemical reaction then they are precipitates okay now other chlorides other bromides other iodides you see them break them down they dissociate 100 these nine guys won't all right so i do want to uh specifically talk about the mercury one plus mercury one ion okay now all right the reason that i called this mercury one okay despite the fact it has a plus two charge here is that you notice this also has a subscript okay now and this ion metal ion here you can actually view it as a poly kind of a polyatomic ion no between the two mercury mol atoms okay there is actually covalent bond okay and together these two shows a plus two charge to the outside word and of course no if you put the char you put the charge on each of them each each mercury is only losing one electron together the two of them lost two electrons and that's the plus two charge and this one is kind of special because if you look at these three formulas you don't normally see now ionic compound formula like this okay remember nacl you would never write it as na2cl2 okay because we said before okay ionic compounds um are in three dimensional array they don't make molecules and when they're in three dimensional rate we're going to take the smallest whole number ratio okay two to two is one to one so use one to one and then now if that's the case why did you use two to two here why didn't you do this as hgcl well this time hgcl would be wrong why because again we just told you that this is a special polyatomic ion okay these two do stay together they're bonded together now remember when we were talking about sodium chlorate we say well your two sodium ions wouldn't stay together so you can't write it this way because they both have positive charges they hate each other they push each other away this two mercury have no choice but staying together they're bonded together okay so although this looked like a two to two ratio this is essentially a one to two ratio for for these three compounds it's one hg2 two plus ion and two chloride bromide or iodide io it's essentially a one to two ratio so this doesn't conflict with our idea of ionic compounds should have the smallest whole number ratio you're still one to two is still the smallest whole number ratio okay now it's not a two to two ratio here okay but this is kind of a side knowledge nugget that you know you might get confused on later on when you read this i just want explain it clear okay but coming back to our main main point rule number three of solubility rules is chloride bromide iodide compounds are soluble except when they're combining with these three positive ions rule number four is also a soluble with exception rule and this time we deal with only one negative ion okay now sulfate ions okay compounds are soluble except when combine so same wording with this time six positive ions three you are you already are familiar with silver ion lead ion and mercury one ion and then calcium ion strontium ion and barium ion now how do i remember these three well if you know your strong bases you already know these three ions okay the five positive ions in group one and these three positive ions together eight of them gave you the eight strong bases their hydroxides are the eight strong bases so you already know this group and you already know this group from rule number three and all six of them okay makes sulfate ions precipitate makes sulfate ion insoluble so silvers sulfate ag2 so4 lead sulfate mercury 1 sulfate calcium sulfate strontium sulfate and barium sulfate these are the six sulfates that's insoluble or you can say if they're made in a solution chemical reaction on the product side they're going to be precipitates all right now rule number five so rule number one and two are soluble rules rule number two three and four are soluble with exception rules okay rule number five and six are mostly insoluble rules so the wording here is oxide ions and hydroxide ions their compounds are insoluble except when combined with group 1a and calcium strontium and barium ions okay so you are having a whole bunch of ions again i'm gonna have to remember group 1a you said it's five ions of these three three more so eight ions was combining with two negative ions 16 possibilities i need to remember all of that it's too much not really okay like i said on rule number four okay you already know this group okay you know you know them from the strong base well look at the eight negative positive ions here okay and look at hydroxide if you already know your a strong base which you really should okay because you're going to see them a bunch on your exam too okay if you already know these your strong bases you've got nothing to memorize here okay of course these guys together with hydroxide are soluble okay yeah of course they're soluble these are the eight strong bases okay this also answer your question when we were talking about strong basis like what about something like you know copper hydroxide magnesium hydroxide why don't why aren't they strong bases simple okay their hydroxides are insoluble and if it can't dissolve if it cannot dissolve in water can can it give you a strong base solution of course not okay so you know your strong base you know the ions involved in here now why did you involve oxygen generally speaking okay oxygen compounds okay uh why do you in involve oxide not oxygen now generally speaking oxides okay our metal oxides are mostly insoluble okay yeah and majority of the rocks on earth okay are made of especially you know different mines okay not coal mine coast coal is basically carbon okay but different kind of iron minerals copper minerals all those rocks okay they're different metal oxides combination okay now they don't dissolve okay they're insoluble and even these guys the group 1a and calcium strontium and barium oxides when you put them into water they're not exactly dissolving now of course let me give you an example okay sodium oxide okay sodium oxide is such a reactive solid reactive compound that the moment you put it into water okay don't expect this thing to go into na plus and o2 negative okay that doesn't happen so what does happen no going into water you're gonna end up with two sodium ion okay and that oxygen so two sodium two sodium comes off that oxygen is going to due to water okay it's gonna take one hydrogen away from the water okay oxide is negative two take one edge plus in so that's why you get an oh negative and if you take one h plus from water what you got left you have another hydroxide so these guys are going to react with water group 1a metal cation metal hydro metal oxides are going to react water with water and still get now strong base okay and similar for calcium strontium and barium these guys can react with water and make calcium ion and two hydroxide ion okay this is why these eight no metal oxides are called base anhydrides okay because you put in water to these oxides they're going to react they're going to disappear they're going to dissolve and they're going to give you a strong base solution okay so really rule number five solubility rule number five is all about the strong base okay hydroxides are strong base and oxides when you put them into water are going to end up in strong base okay and if you compare this to rule number one you do notice that like where in group one you said anything with group 1a and also ammonia ammonium should be soluble what about ammonium with hydroxide or ammonium with oxide sorry wrong place well ammonium and oxide won't make a compound period okay these two just don't get together okay ammonium and hydroxide could get together okay but when these two get together now the result is not a ionic compound now you don't have we don't normally write it as this you could okay but we don't normally write it as this because this thing now can quickly break down into regular ammonia with three hydrogen and a water molecule okay so whenever you have ammonia and hydroxide getting together you ended up getting a molecular compound it's not not exactly the salt the full 100 percent dissociation that we were discussing before and that's why it's not included in here okay now so that's rule number five rule number six rule number six is kind of a everything else rule okay the ions that we didn't talk about here ionic compounds containing f fluoride ion sulfide ion carbonate ion phosphate ion chromate ion are insoluble except when combined with group 1a or ammonium ion okay now do you mean that i need to recite memorize another rule in involving a whole bunch of negative ions remember all a whole bunch of negative ions and then you know the rule and the positive ion again you don't have to memorize it like that and like i said this is what we call the everything else rule in k115 okay all the other negative ions that's not showing up in rule two through five okay you can put them into this category you run into a negative ion that you don't remember seeing in rule two three four five it belongs here you can assume that it's one of these okay and you can assume that their compounds are insoluble but if you already have rule number one remembered rule number one is these guys are soluble with anything okay you can't go contradict that so except for the group the rule one six positive ions all the other negative ions combined with all the other positive ions to produce you insoluble ionic compound how about that now so now again now solubility rules is a set of rules that's generalized for uh to simplify our understanding of the material here in chem 115 okay now it didn't take us to go very far in in the chemistry path to ditch it okay some a lot of you would go on move on to chem 116 by the time we get into chem 116 we're gonna tell you that okay we don't at some point we're not using solubility rules anymore because there's more complicated there's more in-depth understanding that we would have on these ionic compounds okay but right now i'd rather have you understood this as a black and white soluble and insoluble okay applying the rules and now for your exam too you absolutely need to know these six rules of solubility like the back of your hand okay or better than that no you just need to know them and not only you need to know them you need to be able to look at a compound and quickly make a judgment which pro which compound is soluble which compound is insoluble which ones can i dissociate into ions which ones can i not dissociate into ions okay because you're gonna do a lot of that like even for let's say think about it for a solution chemical concept equation problem okay let's say i gave you five chemical equations and ask you know which one contains you know it's a precipitation reaction what do you need to look at you need to look at at least 10 products two for each choices and judge on their solubility okay and it definitely cannot take you a question like that definitely shouldn't take you five minutes ten minutes to look at every single compound and trying to recall the solubility rules in your mind you've got to be able to look at those compounds and then just instantly write on it right now soluble insoluble soluble soluble insoluble insoluble okay yeah so your understanding your office solubility rules gotta be to t to that level for you to use it you know in your exam and without making without wasting too much of your time and i don't like memorizing contents in a chemistry class because i firmly believe this is more about understanding than memorizing but there are things like you have to memorize now going through a science class like this and this is probably very high on that very short memorizing list know your solubility rules okay now so now that we know how to predict products of two electrons of the reaction between two electrolytes how to break down okay those molecular formula of the compound into a full uh from a molecular equation to a full ionic equation how to cancel the spectral ions in full ion equation to get net ionic equation okay now let's discuss a few different reactions they're all double displacement reactions okay but during the process of predicting products and you know predicting full ionic equation predicting net ionic equation there are lots of things that you need to be careful about otherwise you might end up getting a problem or getting a wrong answer in the exam so let's see a few examples now first of all now does all double this ransom reaction happen okay what do you mean well it looks to me like you can come from what we did so far you can combine any two electrolytes and as long as they don't contain the same ions okay you can always exchange partner and get something different for a molecular equation does that mean those reactions happen every single one of those reactions that you can write you can predict always happen not necessarily okay so let's take a look at this next example here okay n a no3 react with cu so4 okay we want you to predict possible product get the full ionic equation and get the net ionic equation and identify the possible now identify the possible um spectator ions all right so let's do that first of all you got to exchange partner okay we after a couple lectures you should be fairly familiar with this okay sodium is plus one nitrate is negative one sulfate is negative two that that means your copper is plus two all right so sodium i'm gonna go with sulfate copper is gonna go with nitrate so copper nitrate plus two negative one so i'd better have two of these okay and then sodium and sulfate plus one and negative two i better have two of those and then of course make sure your equation is balanced you put your two here then okay i got a molecular equation two electrolytes exchange partner and making me two more two different electrolytes all right so what's the full ionic equation okay let's let's go anything contains sodium or nitrate are going to be soluble so two positive ions two negative polyatomic ions okay copper sulfate rule number four is about sulfate sulfates are soluble except with silver lead mercury calcium barium strontium copper is not one of them so soluble sulfate ion and copper ion now and then so left side two strong electrolytes two soluble salts all broken down on the right side okay anything contain nitrate is soluble so copper ion soluble 100 dissociation copper ion to nitrogen anything contains sodium is soluble so two sodium ion and sulfate so two strong electrolyte on the right side now so you got your full ionic equation what are your spectator ions let's go two sodium two sodium two nitrate two nitrate two sulfate copper oops i canceled every single one of the four ions all ions in this case are spectator ions what does that mean well if all ions are cancelled as spectator ions do you have a net net ionic equation of course not no net ionic equation well no net ionic equation means what remember when we first introduced net ionic equation in the last lecture we said net ionic equation is the real chemistry remembering that neutralization reaction we said h plus and which negative are going to neutralize each other and turn into one molecule that's the real chemistry in the neutralization reaction new net ionic equation means what no chemistry no reaction nothing happened but i i did write a chemical equation that chemical equation doesn't mean anything because you don't have these compounds binded together in the solution you don't once you put them into water in solution they're three ions on the left side you have two three ions four free ions on the right you have the same four free ions nobody did nobody found their soulmate well no chemistry okay so this should answer that question like okay i does any two ionic electrolyte okay always come without common ions without the same ions always combine and make a chemical reaction the answer is no okay if you end up having four strong electrolytes in reaction then you can pretty safely count that as no chemical reaction at all all right so that's one example now previous page so ammonia and hydroxide when they get together gave you ammonia and water molecule here's another one okay sulfuric acid and calcium hydroxide oh okay that one is easy suffering acid is one of the seven strong acids you told me okay one hundred percent no 100 dissociation and everything calcium hydroxide is one of those eight negative uh one of those eight strong bases you told me okay five in group one a then calcium strontium barium so eight strong bases oh strong acid and strong bases shouldn't the yellow equation be plus plus plus oh negative equal to water molecule well let's see now so reaction of course is exchanging partner h and o h getting together calcium and sulfate get together okay this is plus one this is plus one this is negative two this is a plus two this is negative one so water h and o h getting together plus one negative one getting me water and since i have two or two of each that's going to give me two water calcium and sulfate plus two and negative two perfectly together now all right so now that is a neutralization reaction and we can pretty safe to say we can feel pretty safe to say that this is going to happen for sure not like our last example no because you did make something you can't dissociate this that's not a strong electrolyte there okay so strong acid 2h plus so4 strong base calcium hydroxide to water you can break down water and then calcium sulfate if you quickly go this is gonna dissociate you're wrong why oh rule number four sulfates are soluble except when combined with what super red mercury one calcium strontium barium o calcium sulfate is an insoluble ionic compound as a product in this reaction this is actually a precipitate that is your full ionic equation now do you have any spectator ion in here is there anything on the two sides that's the same you can cancel if you wrote it wrong then you have calcium and you have sulfate you can cancel right now do you your calcium and softly got together and they got out of the solution into this solid precipitate at the bottom of your beaker is that the same with your free moving calcium ion and free moving sulfate ion in the solution before this happens of course not and if they're not the exact same can you cancel of course you can't so no spectator ion in this reaction and your full ionic is your net ionic equation for this reaction makes sense all right now one more here's another neutralization reaction okay happening between an acid and a base a base the base is a strong base the acid if you think about your strong seven strong acid list phosphoric acid is not part of your seven strong acids okay so this is a weak acid now first of all let's predict products that should be easy sodium is plus one hydrox is next to negative one hydrogen is plus one you have three of them phosphate is negative three okay so sodium is going to go together with phosphate hydrogen is going to go together with hydroxide sodium phosphate plus one negative three so you're gonna need three of those to offset the charge okay and then hydrogen and hydroxide is gonna make you water and you're gonna need three sodium hydroxide to satisfy the three sodium need and also three hydroxide can work with those three h plus and gave you three water okay so i predicted my molecular equation pretty easily now what about four ionic equation okay so that's a strong base okay easy 100 dissociation means three sodium ion and three hydroxide ion okay and this is nasa so three h plus phosphate oops you're wrong again okay what do you mean like their acids don't acid all acids are electrolyzed and dissociate yes okay all acids are electrolytes and dissociate but the only the strong acids dissociate 100 okay so if this is one of those seven strong acids no doubt in in your mind okay break it down into etch plus ions and negative ions but this is not okay you have a weak acid here so what should i do with my weak acid remember weak acids have partial dissociation okay and matter of fact vast majority of your weak acid molecule regardless what kind of weak acid you have mass vast majority of your weak acid in a solution stays in the molecular form only a small portion of your molecules break down into ions okay and that's why for all the weak acids you have to keep in your reaction the chemical formula in the molecular form okay you have to okay because this is the main presence of your weak acid in the molecular form a little bit of it dissociate into ions okay yeah and if you're wondering well if you say only a small portion of dissociate does that mean only a small portion of the ions are free and can get together and then your reaction would never get to the end you would never be able to consume the rest of your h3po4 that's not the case okay only a small portion of h3 the weak acid can dissociate okay the ones dissociate made the three ions and these three ions will react with the strong base you have here well after you consume these weak acids these free ions made by the weak acid okay remember we cast it in a solution okay always dissociate some once these hydrogen ions are consumed okay you don't have dissociated weak acid anymore so this weak acid the leftover weak acid molecules is going to dissociate a little bit more small portion and then those are going to be reacted and then you're going to need to dissociate another small portion so on and so forth eventually this reaction still goes to the end okay but when you're writing the formula the chemical equation you have to keep it in molecular form and then okay anything contains sodium is soluble so three sodium ion and a phosphate ion you have to dissociate that and water is a regular molecule you can't dissociate that all right this is your full ionic equation okay what about net ionic equation well what are your spectator ions do you have any speculator ions here oh sodium is never going to find a soulmate okay matter of fact none of those 12 ions in the first two rules is ever going to find the soulmate and that's just the way it is okay they're they're spectator ions no well i get i take that back like some of them no you can you you're going to see now ammonium when they get together with hydroxide it can still ended up being a um a weak electrolyte and so sodium though okay let's just focus on sodium here sodium no matter where it is it's always going to be a spectator okay now because it when it makes salt it's soluble when it makes base it's strong base okay it's always 100 association for sodium anything contains sodium now all right so that's the full ionic that's the spectator and what you got left so h3 po4 plus three hydroxide producing phosphate ion and three water that is your net ionic equation okay no and now remember the weak acid weak base wherever they are as long as they're in your equation okay you can't break it down you can't dissociate it okay here's another example having the weak acid or weak base on the product side okay imagine that you have ammonia ammonium nitrate reacting with potassium hydroxide okay so plus one negative one plus one negative one exchange partner so kno3 101 and nh4oh well remember that if you go back to so instead of writing that ammonia and water molecule okay now dissociate dissociate dissociate dissociate soluble salt with ammonium nitrate and strong base with potassium hydroxide soluble salt with potassium nitrate why because potassium and nitrate are both soluble ions potassium and nitrate plus ammonia and water nitrate cancel potassium cancel oh so an h4 plus react with hydroxide produce ammonia and water molecular equation full ionic equation net ionic equation so a conclusion you can come to at this point is that let me generalize it for you okay for a double displacement reaction to happen okay you gotta con your reaction gotta contain okay as a product either one a precipitate or insoluble if you made an insoluble ionic compound okay that means you're going to have a molecular formula or a formula unit you can dissociate which means they can't be cancelled and if they can't be cancelled you absolutely are going to have an atomic equation so if you have if you make a precipitate okay your reaction double displacement reaction is definitely going to happen if you make a molecule or a molecular compound like water like ammonium and you will probably talk about a couple more in the next class okay if you're making a molecular compound then your reaction definitely is going to happen if you're making a weak electrolyte like a weak acid or a weak base then remember we don't dissociate them so your reaction definitely happens and if you're not getting one of these things and you have four strong electrolyte in your equation you've got no chemistry everything is a spectator ion everything cancels we'll pick up from here on the next lecture