so let's move on to chapter seven we're going to tackle the very end of chapter seven the only topic we really jumped into in the end of six was mass percent in chapter seven we're going to be digging back into the idea of solubility and moving into precipitation reactions and predictions that we can make with those so we're going to be using the solubility table a bit so if you have a copy of this keep it handy it'll make it easier while we're going through lecture if you can reference it when you need it all right so when we were back in chapter 7 we talked a lot about solubility and insoluble and soluble compounds and now we're going to kick that up a notch so let's say that i have two aqueous solutions remember aqueous means dissolved in water so these are ionic compounds both of these are actually both the potassium iodide and the lead ii nitrate now both of these compounds are soluble we don't have to look it up because they say they're aqueous they say they're dissolved in water so if they dissolve in water ionic compounds are going to separate into their ions so this ki is going to separate into both k plus that's aqueous and i minus that's aqueous this pbno32 is going to separate out into pb and two nitrates if we remember our polyatomic ions we've got a chart available even for exam three these nitrates carry a minus one charge so if i have two negative charges that's a total charge of negative two so this pb must have been plus two to counter that charge cancel it out make it zero so when we have a solution an aqueous solution of ki this means we've got k plus and i minus ions in solution in our solution of lead 2 nitrate we've got pv2 plus ions but we've also got nitrate ions in solution now if we take these two separate beakers these two separate containers and we mix them together we now have one larger beaker that contains all of these ions so this mixing allows different pairs to form now depending on what pairs form we could take an aqueous compound and an aqueous compound and a solid can form in this case it does when a solid forms when we have two aqueous mixtures we've got a precipitate so the precipitate is the solid that forms and we would call this a precipitation reaction now this is brightly colored yellow you notice it wasn't before and that's because when this reaction takes place you form this beautiful school bus yellow color if you look on blackboard i've left a video alongside the lecture where you can see the formation of this beautiful yellow compound okay not all roads lead to precipitation though now if we look at potassium iodide and sodium chloride again these both start out as aqueous which means that these are dissolved in water these were soluble compounds but when i mix those two together i get no solid so what that means is my products i had no real reaction no solid was formed and that means that everything and i'll write it here everything was soluble which means it was aqueous remember when we said things were aqueous these are dissociated ions they weren't lumped altogether they weren't bonded together instead they were free ions in solution so only insoluble products the ones that won't dissolve and these are the ones that form solids those are what go on to form your precipitates those form your precipitation reactions so it's almost like a game of duck.goose where you have aqueous aqueous solid so precipitation reactions two aqueous solutions combine and form an insoluble and let's add here if it's insoluble it's going to be a solid compound that solid insoluble compound that's your precipitate but in the case of mixing ki and nacl we had no reaction because everything was soluble everything stayed aqueous and no solid formed so actually before we move on let's take a closer look at this if i have ki iodide and its aqueous and it reacts with nacl which is aqueous we're going to have a double replacement reaction happen which means our k and our n a are two cations and these aqueous compounds are going to swap they're going to switch places so when i get over to the product side the n a is going to be paired with the i now and the k will be paired with the cl and i'm not going to write my phases just yet i'm going to come back to our solubility table now if i look at sodium and potassium if i have salts that contain na plus and k plus it says these are mostly soluble which means they're mostly going to dissolve and if they dissolve and we're working in water we're looking at aqueous were there exceptions for lithium and sodium let's read across no exceptions they're just mostly soluble so when i go back here after mixing i've got a salt that contains sodium so yeah that's going to be soluble it'll be aqueous and kcl again that's going to be aqueous so because no solid formed over here i had no reaction everything stayed dissolved and no precipitation reaction occurred so let's work through one of these from start to finish and we're going to try to predict whether or not a precipitation reaction occurs and we're going to learn something as we go through all the different steps so when we did our last reaction we did a double replacement reaction where we took the cations the metals here and we swapped places so when we get over to the product side if we combine aqueous solutions of agno3 and nacl they're going to swap what they're paired with so ag is now going to be paired with cl and n a is going to be paired with no3 now when we got over here let's make sure we wrote these formulas out correctly we said nitrate has a negative one charge that's off the table that you have on your formulas and equations page for the last exam and for the coming exam and if it carries a negative one charge and i've got one of them then the silver has to be a plus one to balance that out so let's carry that idea over here if this silver is plus one well chloride is in group 17 on the periodic table and those tend to form a negative one charge so this formula looks good a g at plus one and c l at minus 1 those charges are going to cancel out and we'll have a overall neutral formula so let's take a second look at the next chemical formula so this one group one on the periodic table is going to carry a plus one charge we said that nitrate is a polyatomic ion with a negative one charge so we've got one sodium one nitrate those charges are going to cancel out and we'll be left with an overall neutral compound there now what we haven't done is we haven't put any phases on these we started aqueous and now we have to figure out what goes here and what goes here for the phase and where do we go for that we're going to go to the solubility table so let's look up hecl and nano3 so let's start with a gcl that's going to dissolve to give us a g plus and cl minus if it dissociates so let's take a look at these two ions so i've got cl minus that shows up here and it says chloride bromide or iodide are mostly soluble so they'll dissolve but then when we read across it says they'll dissolve except when they're paired with something like silver ag plus so this would be soluble but since the silver is here that means this is going to be solid it's not going to form ions it's going to form a solid excuse me okay so let's go back and at least for one of these now we can say we form a solid remember if i form a solid here that's going to be my precipitate that means that a reaction occurred a precipitation reaction so let's go back real quick and look at excuse me look at nano 3 our second product just for the extra practice now i've got nitrate in that nano nano3 really we only need to look up one of these so nitrate is mostly soluble and if we read across there are no exceptions so that means that if it's soluble then this is going to be aqueous it's going to dissolve so this way that we wrote this out this is called the molecular it's a horrible term because these are ionic compounds but this is the molecular equation the molecular equation shows everything's still grouped up it doesn't show anything dissociated or broken up into its ions just shows everything's still paired if we wanted to go the next step we could go to the ionic equation that's where everything that's aqueous is going to be separated into its ions so agno3 we would have a g plus which is aqueous plus no3 which is aqueous but this gives you a better picture because if it's aqueous and it's ionic that means it's going to be split up like this for nacl when we split that up i have one n a i have one cl so i'm going to have an n a plus and a cl minus these are both going to be aqueous now when we go to the other side this agcl is solid we've only been dissociating or breaking up aqueous compounds we're going to leave the solid b it's going to remain intact so it's going to be agcl solid and then to that we're going to add this last compound but it's aqueous again so we're going to split this one up into a single n a plus plus a single nitrate where both of these are aqueous now this right here is called the ionic equation because it shows all of our aqueous compounds dissociated into their ions now there's a third way to represent this and that third way is called the net ionic equation if you look at your gross pay versus your net pay your net pay is always smaller on your paycheck your net ionic equation is always going to be the smallest and simplest of the three it's where all the interesting stuff happens so let's get a different color pen here and i want to look at that ionic equation more closely now on the ionic equation i've got no3 minus that's aqueous on this side now i've got the exact same thing over here i've got n a plus that's aqueous on this side and n a plus that's aqueous on the right side so what i crossed out and i'll write it here ions that cross out are called spectators so these spectator ions just like spectators in a sports game they don't really take part in the interesting chemistry they remained unchanged they're spectating the actual chemistry that's at work now what's left over is our net ionic equation and what's left over is an ag plus that's aqueous plus the cl minus that's aqueous is going to form agcl that's solid and this would be our net ionic equation the net ionic equation hold on just a second this net ionic equation is going to show our precipitate on the right being produced the ions that make it up are going to be on the left we specify charge and how many we specify the phases all the way across the board and we've got our net ionic equation now did a reaction occur here just to recap yes because we took two aqueous solutions we formed a solid because we formed a solid it was our precipitate and we had a precipitation reaction occur all right let's try out this next one we've got sodium carbonate reacting with copper two chloride okay so just like last time we're going to be swapping out our metals our cations so copper started out paired with chloride but now copper is going to be paired with carbonate we had sodium paired with carbonate now it's going to be paired with chloride now sodium is in group one on the table so it's plus one chloride is group 17 on the table so it's -1 these charges are going to cancel and that makes nacl a good formula it's already charge balanced let's take a minute and look at our other formula copper is a transition metal so it's a little tricky so we have to spend a moment on it where we had it over here we said chloride is in group 17 and has a negative one charge i've got two chlorides that gives me a total negative charge of negative two i've got one chloride that means to balance it out that copper has to be a plus two to balance the charge so the negative two from my two chlorides the positive two from my one copper make the charges cancel so why did i do that because i have my copper two plus over here that means the copper is plus two here if we look up carbonate on our list of polyatomic ions carbonate has a negative two charge so the positive 2 from the copper cancels out the negative 2 from the carbonate so we've got a good formula there so let's clear this out and just like last time we started out here in writing the molecular formula whoops here's my pen so this is the molecular equation it shows everything's still paired up doesn't show any aqueous compounds dissociated we haven't written in our phases yet because we haven't looked at the solubility table now this is table salt so let's just use a little bit of insight does table salt dissolve absolutely we could look at the solubility table but i think we can make the judgment call the table salt dissolves in water so this is going to be aqueous now let's go look up copper ii carbonate okay so i don't see copper anywhere on here but what i do see is carbonate but it's on the bottom of the table now it says carbonate is going to be mostly insoluble so won't dissolve so that means it's going to be a solid so if carbonates won't dissolve the only exceptions are group 1 metal ions and ammonium well that's not copper copper is not an exception so carbonate won't dissolve so if i go over here that means this copper carbonate if it won't dissolve it'll be a solid so that makes this my precipitate and that's going to be a precipitation reaction that occurred so we don't have a no reaction we do have a reaction to happen so let's write out our ionic equation that's where we take all of our aqueous compounds and separate it out into ions i've got two sodiums in sodium carbonate so that's going to be two and a plus those are going to be aqueous i've got one carbonate ion right here don't mistake that for three of those that's co32 minus is one carbonate ion that's going to be aqueous because when it's aqueous that's when we split it i've got one copper and two chlorides so i'm going to separate that into cu 2 plus aqueous plus 2 cl minuses that are aqueous now we hit the reaction arrow we get our solid which that's the one we don't separate we don't dissociate solids into ions this is solid plus nacl we're going to dissociate so that's going to be n a plus plus c l minus those are both going to be aqueous now we missed one thing but we're going to go back and fix that we didn't balance the overall reaction so we still have to use our balancing skills that we picked up in the last exam's material i have two sodiums here so to balance that i've got to put a two here that gives me two sodiums that gives me two chlorides i've got two chlorides one copper one copper one carbonate one carbonate so the only thing we really had to change there is putting a two in front of the nacl so now we're gonna get two na pluses and two cl minuses when we broke it all up this would be our ionic equation where we show all of our aqueous compounds dissociated into their ions okay so our last here was the net ionic equation to do that we had to cancel out our spectators so n a plus i've got two of them on this side that cancels with the two and a pluses on this side two cl minuses on this side cancel with two cl minuses on the opposite side my two spectators were let me label these spectators were cl minus and n a plus i had two of each now if i want to go the next step and write my net ionic equation it's whatever is left so it doesn't matter which one we put first it's traditional it's normal that you would put the cation first here so co2 plus wouldn't be wrong if you started with carbonate though this would be aqueous we're going to add to that co32 minus and it's aqueous when we start that's going to go to form copper to carbonate so cu co3 solid and that would be our net ionic equation the shortest of the three remember that the solid was our precipitate that we formed because we formed a solid that's a precipitation reaction we do have a reaction occurred so if you look on blackboard we've got a number of other chances to practice and watch videos on precipitation reactions this was the lead iodide video that i was talking about we can also look at the formation of soap scum as a source of precipitation so where do you find these videos in practice well if you go to our exam 3 materials inside videos tutorials and practice you'll find extra practice for both the mass percent for the end of chapter six and for precipitation from end of chapter seven so uh good luck with this new material and let me know if you have any questions