all right in today's lecture we're going to take a look at precipitation reactions in the process of precipitation and that's going to segue us into a much broader to topics well without further Ado let's get things started let's get things started by taking a look at the precipitation reaction of lead to nitrate with potassium iodide all right here's one of my favorite classic examples of a precipitation reaction I have pottassium iodide and I have lead to nitrate and if we look in we can see that they're both liquids right no solids matter of fact might Leed to nitrates rather clear my potassium nitrate is also very clear kind of a yellowish tinge but it's clear you can see there's no particulate matter in it we're going to perform a precipitation reaction where we take two salts that have been dissolved in water and are soluble in water however when we mix the two salts we wind up forming a solid and this solid is going to fall out of solution we call things that fall out of the sky such as rain or snow precipitation we call things that fall out of a solution a precipitate so we're going to form a precipitate got my potassium um tastic mide here going to pour it into my lead to nitrate dramatic Action Shot zoom in whoa whoa look at that look at that and what you'll see here is I now have not just a color change but if you look at the sides of my beakers there you'll see that I have little particles specifically little particles of lead to IOD that Leed to iodide that's now come out of my solution is a precipitate and what you're going to learn in today's lecture and in today's lab is how to predict when a precipitate is for going to form oh look at look at that look at that look at all that Li to nitrate there all right chemistry's easy life is hard all right so now you've actually seen a precipitation reaction specifically what is it that we were looking at we saw in that demonstration that we took lead to nitrate oous we reacted it with pottassium iodide aquous and we produced lead to iodide solid and [Music] and potassium nitrate aquous we saw that a solid came out of the solution that yellow those little yellow granules those little yellow granules where your lead to iodide and it's referred to as your precipitate just like we have things falling from the sky and we call stuff that falls from the sky precipitation we things we call things that fall from a solution a precipitate solid that comes out of a solution is referred to as a precipitate now the great thing about precipitation reactions is that they're really love stories if we look at what really occurs during a precipitation reaction we can see what we're talking about remember we talked about electrolytes and we said that anytime you have an ionic um compound dissolved in water it's like the ionic compound got a divorce we have lead 2 nitrate here and it's aquous that means that H that if we looked inside our Beaker that contained our lead 2 nitrate we wouldn't find lead to nitrate as a unit right we would actually find a solution of water that contained a bunch of lead ions floating around and a bunch of nitrate ions floating around why because they decided that they were more attracted to other water molecule more attracted to water molecules than they were to each other right it was nice while it lasted they dated for a while but man those water molecules came through with those nice positive and partial positive and partial negative charges so they split up same for potassium iodide Splitsville they got together too young they realized how much they'd Grown Apart when the water molecules came along so if we looked inside our beers before we carried forward the reaction we'd see a bunch of lead to lead two FL ions floating around a bunch of nitrate floating around and in our other Beaker right these this is one Beaker and in our other Beaker we'd have our potassium ions and our iodine ions floating around right when they're dissolved in water your ionic compounds have split up into ions well when we mix them together and put them in one Beaker what have we done we've doubled the dating pool right previously our lead had been stuck in a dating pool where the only things to date were nitrate ions which it didn't get along with or water molecules which were nice but it's really looking for an ion well when we mix these two solutions together suddenly there's a new Ion with a negative charge for led to date the iodide ion right so those two are going to go out on a date and what happens Happy Happy Joy Joy it's true love turns out that our lead and our iodide are so attracted to each other that they decide to get married and they leave the dating scene right they literally fall out of the dating scene they literally precipitate out out of the dating scene these guys have found true love they are more attracted to each other are lead in our iine are more attracted to each other than they are to the water molecule well you know how it goes the X's are hooked up so we're going to try to make them Jealous by hooking up as well just because it seems the thing to do not only that but we're going to have to be there sometimes together on holidays and weekends so the potassium and nitrate Tri dating however they don't really have any attraction for each other they'd rather dance around with the water molecules then get married so even though the potassium and the nitrate date and they're in the same dating pool it looks like they're together because we list them together but how do they exist really well they're aquous so they're not finding true love they're really still out there floating around in the water water so if I'm to do a little cleanup here what we could actually say occurred in this reaction is we could say from an ionic perspective that we had lead and nitrate breaking up we had pottassium and iodide breaking up they all four find themselves at the same Club awkward however it has a happy ending because our lead and our iodide finding each other get married leave the dating scene they fall out of solution to perform form of precipitate not so happy an ending for our potassium and our nitrate however even they go on though they go may go on a few dates they don't find true love and they wind up going back and floating around that great discotech of water when we write chemical reactions we write chemical reactions like this right that's how we're used to viewing chemical reactions and how we're used to viewing chemical reactions is referred to as a molecular equation what I just wrote for you down here in this big circle this is how things physically exist right this is how our compounds and our ions are physically existing right our soluble compounds physically exist as separated ions our precipitate physically exists as a solid of lead and iodide desperately clinging to each other and the great Romance of a precipitate this equation that shows how things physically are is referred to as a ionic equation if you look at this ionic equation our love stories cluttered by talking about the X's right potassium appears on this side of the equation and this side of the equation unchanged same for our nitrate pottassium and nitrate aren't finding true love so why clutter up our story by talking about the ex's right who starts off a great Romance by talking about their exes oh wait Ted Mosby does matter of fact Ted Mosby goes on and talks about I believe they said it was 27 different exes before he talks about his current current wife but anyhow I digress great show if you've never watched it Netflix it netfli it um but as chemist we often want to clear the scene and we clear the scene by representing what's physically occurring by Crossing out those things that aren't part of the story in our ionic equation here potassium is the same on both sides of the equation so is our nitrate so if we were interested in telling the core story of the reaction we're really focusing on just the two ions that fell in love our iodide and our lead we would say that this is the reaction that actually took place we would refer to this view as our net ionic equation before the end of the next couple lectures I'm going to be able to give you two reactants and you're going to be able to tell me what the products are you're going to be able to tell me the phase that those products are in you're going to be able to write ionic equations and N ionic equations don't worry though this is just a preview we're going to break it down one step at a time hammer style all right let's get started in terms of breaking it down there's a lot of s of little sub goals that we need to achieve the first of these sub goals the first of these sub goals is to predict if an ionic compound is soluble and that may or may not be throwing out a new term for you soluble means dissolves in water and how do we denote something in terms of phases when it's capable of being dissolved in water when something is capable of being dissolved in water we write an AQ next to it for aquous phase the opposite of being soluble is insoluble for ionic compounds that means they would be in the solid phase note for calent compounds if they're insoluble they could be liquid they could be gas they could be solid right but for ionic compounds if they're insoluble meaning they can't be dissolved in water then they're going to exist in that solid phase here so our first goal is for me to be able to give you an ionic compound and for you to be able to look at that compound and tell me if it'll dissolve in water or not before we take a look at that though why don't you write down the word Colts write down the words Colts c l TS Colts in order to determine whether or not an ionic compound is going to be soluble or not you have to memorize some solubility rules sorry no other way to avoid it other than to say the dreaded word memorization however if you're at one of you're at if you're at one of my atome Gamers this gives you a slight Advantage right because instead of memorizing you can print out the next two slides here on solubility rules for solubility and insolubility as a matter of fact if you have not done so already pause me and print them out because this is one of those times where having the hand out in front of you as I'm lecturing is going to be really really useful and beneficial to you I I would even argue crucial to you all right so these are your solubility rules um if I was to summarize them and we'll go through them one at a time here in detail but if I was to summarize them in other words I was wanting to avoid a lot of memorization ionic compounds where you have a Caton with a positive one charge or an anion with a negative 1 charge chances are that ionic compound will dissolve in water that's the quick dirty way of looking at these four rules now you can see just glancing at them they're more complex than that so let's go through them one at a time all right your first rule and this is a rule to which there are no known exceptions if it conflicts with any other rule this rule is always was right Group 1 a elements and ammonia containing compounds are soluble no exceptions how would we rule this how would we use this rule well we would use it like this is potassium carbonate soluble or insoluble well we see it contains pottassium and pottassium is a group 1A element so if it contains a group 1 a element it's soluble so we would know that this would be soluble in water and that's a cursive AQ people are always questioning my handwriting down here we have another compound we have ammonium phosphate is it soluble in water well we see it contains ammonium and anything that contains ammonium is soluble in water so if it too would be soluble in water see chemistry is easy life is hard your second rule is equally as easy any compound that contains acetate nitrate or perchlorate are soluble meaning they're going to dissolve in water so if your ionic compound contains one of those three ions they're soluble in water with no exceptions so we have calcium nitrate is it going to be soluble or insoluble well we see it contains nitrate since it contains nitrate it's soluble in water down here we have iron 2 acetate is that soluble or insoluble well we see it contains acetate remember acetate can be written more than one way we see it contains acetate so it's soluble in water chemistry is easy life is hard and again there are no exceptions to this rule there are exceptions to this rule however most chlorides bromides and iodides are soluble except Silver Mercury 1 and lead two except Silver Mercury one and lead two know these exceptions these exceptions are important what do you think I'm going to ask you on exams darn right I'm going to ask you those exceptions not just because I'm wanting to make your life miserable and give you something extra to memorize I'm going to ask them because they have great deal of use to us in the laboratory when it comes to separating things and Performing qualitative analysises and we'll go into that in more detail later but right now you need to know that most chlorides bromides and iodides are soluble except Silver Mercury 1 and lead two so again let's apply this rule is nickel two chlorides soluble or insoluble it contains chloride and nearly anything that contains chloride is soluble so nickel 2 chloride would be soluble in water how about lead to bromide well most bromides are soluble but wait wait wait we don't get to do it to dissolve our PBJ or PBB if I ever have an element I will so name it J but at any rate are um now I'm totally thinking about lunch anyway it contains lead right and Lead is an exception since it contains lead and Lead is an exception to the solubility rules that means that this is insoluble and it would be a solid or would remain a solid if we placed it in water so it's insoluble because it's an exception our last solubility rule is the one you have to watch out for it's the one that bucks that Trend remember I said most things that have positive or negative ones are soluble look what we got here we have sulfates and to refresh our memory what's sulfate S so4 2 negative most sulfates are soluble the exceptions to this rule can be broken down into two categories for memorization first round up the usual gang of suspects right the same three troublemakers that we had for our chlorides halides and iodides are also troublemakers for our sulfates then we throw in two more then we throw in three more suspects rather than memorize these guys outright look where they're located on your Periodic Chart I know you have a periodic chart in front of you because you wouldn't dream of sitting down for a chemistry lecture without one but if you look on your Periodic Chart group 2A what do you see you see calcium strontium and barium what do you do with the dead chemist well first you try to helium and if you can't do that you hope you can cuum and if you can't do either of those two things then you gotta bury them but at any rate um try the salad bar folks I'll be here all week uh if you look at your Periodic Chart they're all right in a row there in group 2A is that lower part of group 2A calcium strontium and barium so I call them a gang of two for memorization purposes and they'll pop up again as exceptions on other items here later so let's apply this rule most sulfates are soluble so we look at this compound it contains sulfate so it's soluble it also contains pottassium so anything that contains pottassium is also soluble because potassium is a group one a element so that was our first rule there so this has two rules that tell us it's soluble next we see calcium sulfate and we're saying well we see Cal we see sulfate so it must be soluble but then that alarm Bell goes off it sounds like a crow K calling at us reminding us that calcium is an exception to the sulfate rule so because it contains Calcium which is an exception it's going to be insoluble here are the insolubility rules um I was getting ahead of myself there apparently there are also two rules that tell us when things will be insoluble two rules that tell us when things will be insoluble compounds that contain phosphates or carbonates are insoluble compounds that contain sulfides and hydroxides are insoluble note if we were to do a quick and dirty trend for our insolubility rules they all have charges with an absolute value two or greater but let's take a look at these rules one at a time first compounds containing phosphate or carbonates are insoluble the exceptions to this rule are simply our first rule right anything that contains a group 1A element or ammonia is soluble so really this isn't something we need to memorize you just need to remember me remember that our first rule has no exceptions so we see magnesium carbonate anything that contains carbonates are insoluble solid insoluble it would not dissolve in water down here we're getting a little bit trickier we see carbonate so we're saying yay it must be soluble insoluble in water but then what's our carbonate bonded with it's bonded with rubidium and rubidium is in group 1 a and anything that contains a group 1 a element is soluble so this would actually be soluble then we come to calcium phosphate anything that contains phosphate is insoluble is calcium an exception no it's not so calcium phosphate is insoluble remember solid means insoluble then last but not least we have sodium phosphate well even though anything that contains a phosphate is insoluble it's bonded to sodium now remember anything with a group 1 a element is soluble and that rule always takes precedence there's no exceptions to it so because sodium is a group 1 a element our substance will dissolve in water so it would be soluble looking at our next rule compounds that contain sulfides and hydroxides are insoluble now our exceptions expand a little bit if you look our exceptions are no longer just the group one elements and ammonia but now include hey those three suspects we saw before calcium strontium and barium that same old gang of two however last time we were seeing things they made things insoluble this time they're going to make them soluble so they're the same exceptions but they're having the opposite effect so anything that contains sulfide or hydroxide is going to be insoluble let's take a look we have barium sulfide we have a sulfide so that says it's insoluble except barium is an exception so that means that it does dissolve in water we have potassium sulfide anything with sulfide should be soluble except Group 1 a elements darn it so since it has pottassium a group 1 a element it's going to dissolve in water then we have iron to sulfide anything that contains a sulfide is insoluble so it would not dissolve in water then we come over here we see hydroxide anything with hydroxide is insoluble unless it's contains calcium calcium is an exception so it will dissolve in water sodium hydroxide also will dissolve in water because sodium is a group 1 a element however if we had magnesium hydroxide would it dissolve in water no because magnesium is not an exception to the rule so magnesium hydroxide would not dissolve in water I know I gave you lots of examples of the Exceptions there why don't you write down the Bengals write down the Bengals b e n g a LS Bengals I hope everybody's writing down the Bengals all right if we were doing this together face to face I would shut up right now I'd have you do this at your seat and walk around your room room and look over your shoulders and an attempt to make you nervous but sent your not doing this face to face with me at the moment pause the video and try to determine if the following substances would be remain a solid or be aquous if you placed it in water pause me pause me pause me pause me oh come on guys it's not that hard pause me and try it on your own did you pause me some of you out there didn't pause me all right so let's take a look together first up we have strontium carbonate we have a rule that says anything that contains a carbonate is insoluble however is strontium an exception to that rule no it's not so carbonate will not dissolve in water it will be insoluble next we have I'm going to go down here we have pottassium sulfate we have a group 1A element anytime we have a group 1A element our compound is soluble regardless of what it's bonded to so it will dissolve in water next up we have calcium sulfide anything that contains a sulfide is insoluble except for calcium since it's a calcium sulfide it's soluble in water anything that contains lithium which is a group 1 a element is soluble sodium is a group 1 a element so it's soluble up here then we have iron 2 sulfate anything that contains sulfate is soluble barium hydroxide anything that contains hydroxide is insoluble however barium is a exception hey what did you do with the sick chem oh oops I already hold that one um then we have silver iodide anything that contains silver I mean anything that contains iodine is soluble except for silver letter Mercury so this actually will not dissolve it'll remain a solid then we have iron 3 iodide well anything that contains iodide will dissolve in water then we have copper one chloride anything that contains chloride will dissolve in water so it'll be aquous then we have ammonia and anything that contains ammonia will dissolve in water so that's it chemistry is easy life is hard let's keep moving how can these precipitation rules prove useful to us here's a classic chem chemistry example of how they can prove useful and these are the type of questions I love asking on exams um and you'll use quite a bit in the laboratory you'll be at quizzed on this and expect to know this really well for lab but you have an aquous mixture of sfide and sulfate what could you add to the solution to precipitate the sulfate but not not the sulfide in other words which compound which of these four cations I would form a solid with sulfate but not with sulfide well let's see ammonia anything that would contains ammonia soluble well that means it won't form a precipitate or a solid with anything when you add it in an aquous environment same for sodium sodium is a group 1 a element so it's not going to form a a solid with either with anything quite frankly in the presence of a water environment ah [Music] barium let's see barium is an exception to the sulf sulfide rule right anything that contains sulfide forms a solid except for barium barium is one of the few things that sulfide can Bond bond with and allow it to remain aquous however bariums also an exception to the sulfate rule most things that contain sulfate are soluble except when they contain barium so barium sulfide actually wants to be a solid so if we added barium to a solution of sulfate and sulfide it wouldn't react with the sulfide at all but it would react with the sulfate to form a solid so it would be the answer to our question what about silver you're saying here's the problem with silver silver absolutely would react with salt with sulfide and anything that contains sulfide is a solid so yes silver sulfide would form solid however Silver's also one of the solutions to is also one of the solutions is is also one of the exceptions to the sulfate rule anything that contains sulfate is soluble except for Silver Mercury lead in that gang of two so if you added silver to your solution both your sfide and your sulfate would become solids only by adding barium could you allow the sulfate to come out of solution and the sulfide to remain into solution it home with a quick illustration I have a solution of barium and sulfate floating around I mean if I have a solution of sulfide and sulfates if I add barium barium only forms a solid with sulfate right it doesn't form a solid with sulfide so if I added barium to my reaction vessel what I'd get would I'd get barium and sufate forming a solution sinking down to the bottom here but it wouldn't react with my sulfide so my sulfide would remain floating free chemistry's easy life is hard and we'll make use of selective ions like barium in the laboratory to help us separate mixtures of things like sulfide and sulfate all right let's kick the reaction up a notch and use these solubility rules to determine the outcome of a reaction our goal here in this part of the lecture is for me to give you a reaction and for you to be able to tell me what the product is going to be in other words if I tell you you're mixing silver nitrate with potassium chloride I want you to be able to tell me what goes on the other side of the arrow note it's not enough for you to be able to tell me what compounds are going to be on this side of the arrow you need to be able to tell me what phase the compounds on the other side of the arrow are going to be in fortunately this can be done in four really really easy steps all of these steps you've actually met before so really we're just stringing together some old Concepts here all right so let's look at our reaction of silver nitrate and potassium chloride the first thing we want to do is list the ions remember when we talked about electrolytes we said an ionic compound dissolved in water breaks up into ions so we want to break our ionic compounds up into ions you do that using your nomenclature rule the most common mistake I see on these type of problems is people wanting to invent ions if it's not an ion you've seen when you done you've when you done when you did your nomenclature don't do it here all right so we have silver nitrate so we have the silver ion and we have the nitrate ion then we have potassium chloride so we have the pottassium ion and we have the chloride ion so that's step one step two make new compounds by pairing the inside ions and the outside ions remember catons always go first what do I mean by pairing the inside ions with the outside ions this is kind of like foiling in math class remember ionic compounds have to form by reacting species of the opposite charges silver and nitrate have already tried to get together to form a solid and it didn't work out right they enjoy each other's company but there's just no nothing there same for potassium and chloride what's the only other negative charge for potassium today nitrate what's the only other negative charge for silver to date the chloride the pattern that will never fail you it will always hold is your new compounds are going to be formed by mating your outside ions and your inside ions your outside ions your inside ions use your nen clature rules to form your compounds silver is+ one chloride is+ one so it would be silver chloride my other compound would be potassium and nitrate remember your positive ion always goes first second biggest mistakes I I always see positive ion goes first so potassium nitrate again a one to one ratio so those are my two products so I come up here to my reaction I have my two products now I've got silver chloride and I have pottassium nitrate now I need to use my solubility rules to identify who's going to be the precipitate do I have a rule regarding potassium yes anything that contains a group 1 a element is soluble so I know that that is going to be in the aquous phase I have a rule that tells me anything that contains chloride is also soluble except bum bum bu silver which is one of the exceptions to that solubility rules anything with if you anytime you have a silver reactant with chloride is going to be a solid it's not going to dissolve in water so that would be the solid which means that this would be my precipitate or the solid that would come out of the solution finally you need to balance mean you need to make sure that you have the same number of ions in each side and in this equation we do we've got one silver one silver one nitrate one nitrate one potassium one potassium one chloride one chloride let's look at another example where the balancing will become more of an issue all right let's take a look at this problem you have barium nitrate reacting with sodium sulfate first thing we want to do is list the ions remember use the nomenclature rules don't invent ions bariums in group 2A so it would be a ba2 plus ion you've memorized that nitrate is NO3 negative what about this two here we don't care about that two here we won't worry about that too until it comes to our balancing step right now we're listing the ions the ion is nitrate not NO3 sub 2 right list the ions same thing over here right the ion is sodium we've not memorized anything na sub two right sodium's in group 1 a so we know that it's A+ one ion we don't care about the two until it comes time for balancing it's bonded to sulfate again you've memorized that sulfate is to negative for you at home Gamers who didn't memorize the polyatomic ions instead tried to just use a cheat sheat to get through it this is the point in your career where you're going to begin to pay for that decision if you don't know those polyatomic ions like the back of your hands you're going to be in for a world of hurt for the rest of your life so if you've avoided memorizing them memorize them now all right so that's our poly so those are our ions now we're going to make new compounds by pairing the inside and the outside outside inside barium is plus two sulfate is plus is -2 so the compound they would form would be a 1:1 ratio same for our sodium nitrate sodium's plus1 nitrates negative 1 so it' be 1:1 ratio remember catons always go first so that sodium needs to be moved to the front so we'd have barium sulfate and we'd have sodium nitrate now we need to assign phases well anything with a group 1 a element is soluble so we know right away that that's going to be aquous well anything that contains sulfate is supposed to be soluble except what's one of our exceptions to sulfate barium right we just had a whole example previous about that sulfate and barium are going to form a solid so barium sulfate would be our precipitate here now last but not least we need to balance I've got one barium here one barium here so I'm good I have two nitrates here now we have to pay attention to our two we have two nitrates over here we only have one nitrate over here so I need two of my sodium sulfate two of my sodium nitrates I've got two sodiums over here I have two sodiums over here now thanks to that two I just added one sulfate here one sulfate here just like balancing a normal chemical equation did I change my compound to to reflect the fact I had two nitrates no I didn't right I just changed the number of my compound I have once you make your compounds in your second step don't change their identity to balance the chemical equation only use those coefficients like you have been all along all right chemistry's easy life is hard unless of course you're a fan of the bills then your suffering never ends so why don't you write down the bills b i l LS bills I have been so crazy rude I have been hogging all the fun and that's just rude of me here's some fun for you now I am going to share the wealth why don't you um try this one on your own pause me try it on your own and then check back for the solution here in a second hey you guys actually paused me this time because these are just too much fun to resist Kudos now um let's take a look we're going to list our ions we have calcium that's in group 2A we have hydroxide right we have potassium Group 1 a and phosphate you've memorized is 3 Nega we're going to make our new compounds Outside Inside here our ratio is a little bit difficult we've got calcium 2+ phosphate 3 Nega we crisscross applesauce to make our compounds and we wind up with calcium 3 phosphate 2 to get those charges to cancel plus one for the potassium plus one negative 1 for the hydroxide so it's 1:1 ratio there so we now have our two products we've got calcium phosphate as one compound and we have pottassium hydroxide as the other compound now we use our solubility rules and we know that anything that contains a group 1A element like potassium is always soluble no exceptions so that's going to be aquous then we can take then we have potassium then we have pardon me we have our calcium phosphate do we have a rule regarding either calcium or phosphate yeah we have a rule regarding phosphate anything that contains phosphate is insoluble is phosphate and is calcium an exception to the phosphate rule no calcium is not an exception to the phosphate rule so it's going to form a solid and it will wind up being our precipitate and I know some of you have noticed a little pattern here where it seems like that our precipitates always formed by our outside pairing that's just a quirk of how I've written the problems that's not a real rule that's just it's just happened that way the way I've written it's it's not going to happen every time matter of fact I I'll give you some on the test where I designed it so that's not the case um so we have calcium phosphate as our precipitate or solid we have potassium hydroxide aquous so now we need to balance I have one calcium here I have three over here so I'm going to need to add a three in front of my calcium hydroxide that gives me three calciums but darn it now it gives me six hydroxides right 2 * 3 is 6 so I'm going to need six hydroxides over here when I do that that gives me not just six hydroxides but six potassiums as well over here I only have three potassium so what can I multiply three by to get six two so that gives me six potassiums now but it also gives me two phosphates which hey what do you know that's exactly how many I need so now I'm balanced and done boom dropping the mic chemistry is easy life is hard