hello everyone this video is going to be on precipitation reactions and solubility our learning goals are to Define what a precipitation reaction is and to be able to identify whether a reaction is such a reaction precipitation reaction and then we also want to be able to predict the solubility of some common inorganic compounds by learning the solubility rules so first we need to know what a precipitation reaction is this reaction is one in which we have some dissolved substances which react to form one or more solid products so this is the important feature that one of our reactants is solid whereas all of our reactants Right started in the aqueous phase these reactions are also called double displacement or double replacement or metathesis reaction so you may hear this called by these other names when we think about what's happening in these reactions it's really that it involves an exchange of ions and we when we look at some examples of these precipitation reactions you'll see why I say that reactions that are cause precipitates are common in nature and in Industry so in your textbook it talks about precipitation of lead iodide which is shown over here on the left you see that bright yellow precipitate which is the lead iodide formerly this solid was used to form artist pigment right because of that vibrant color I can think about kidney stones right which are very painful as stones that are formed um and these are made from calcium oxalate within the body and then another example would be from Coral so the species of coral can add calcium carbonate precipitate to their reefs to slowly extend their structure and grow so those are just some examples and there are certainly many others so some vocabulary for you to learn when talking about precipitation reactions the first is solubility and we will deal more with calculating solubility and doing more calculations with it but solubility is the maximum concentration of a substance that can be achieved under the conditions right that that are being used so how much of a substance can be dissolved in solution under a given set of conditions um substances that have a large solubility are called soluble so if something can be dissolved in a large extent we call it soluble another vocabulary word will be precipitate so a substance will precipitate when it is dissolved or the conditions are such that its concentration exceeds its solubility so in this example we have thallium chloride right it has an aqueous solubility of 3.2 grams per liter at 20 degrees Celsius so if you have a liter of water and you try to dissolve four grams this will be above the solubility and so not all of it will dissolve and you'll be left with a precipitate at the bottom of your beaker um because you have exceeded the solubility so anytime your reaction or your solution conditions exceed the solubility then you'll have precipitation substances that have a low solubility are called insoluble right so in contrast to Solutions or to substances that are called soluble we have substances that are called insoluble because they have a low solubility and these substances will readily precipitate from solution so in order to know whether substances are going to dissolve and be soluble or if they are going to precipitate from solution we need to know how to use the solubility rules and your textbook summarizes these in two tables you can see that this first table shows us ionic compounds that are soluble so you'll see that it lists compounds that contain certain ions so that's what's in this First Column and then in the second column it tells us some exceptions to these so let's go about this systematically in our first box it lists cations which are going to be soluble and we can see by looking at the exceptions column that there are none right there are no exceptions to this so it means that if I have a compound that has the ammonium ion I know it will be soluble there are no exceptions no anions that I can combine this with that are going to be insoluble right and the same are true for these other group one cations right so sodium and a plus there's nothing that I'm going to combine this with that will give an insoluble compound moving down then we have some of our halogens right so the chloride bromide iodide ions these are going to be soluble except there are some exceptions so when we combine it with silver ions Mercury as well as lead then these would become insoluble right so all compounds with chloride bromide and ion are going to be soluble except these exceptions right so if I have silver chloride or silver bromide or silver iodide right those would be the exceptions with silver I could have mercury right so Mercury chloride Mercury bromide Mercury iodide right those would be exceptions and then lead right so lead chloride lead iodide lead bromide is the one I'm missing so these would be the insoluble exceptions for these normally soluble um anions next we have fluoride we can see that that is going to be soluble except when it makes compounds with group two metal cations lead as well as iron we've got lead two plus and iron three plus so the exceptions here would be the group two metal cations so something like calcium which would give us cif2 this would be an insoluble exception we could have lead right so lead fluoride that would be an insoluble exception and with the iron three plus ion we would have f e f 3 right this would be insoluble as well moving down further we've got some molecular ions so this would be the acetate ion this would be bicarbonate nitrate and chlorate these are always going to be soluble because we have no exceptions and then lastly we have sulfate so4 2 minus you can see that this is always going to be soluble except when combined with these different ions so for example we could have silver sulfate right and this would be insoluble or for example the barium ion so barium sulfates would be insoluble I could also write the strontium compounds ionic compounds so this would be insoluble as well so these are just some examples of the exceptions that would form insoluble precipitates with sulfate and now this table shows us the compounds that are usually insoluble and here we have carbonate we have chromate phosphate and sulfide these are always going to be insoluble and then we list only some exceptions now because we have switched the way we are writing this table right it's telling us that these are always insoluble and the exceptions will be the ones that are soluble so a group one cation right so say we have sodium that forms an ionic compound with the carbonate this will be soluble because this represents the exception we could also write an ammonium ion that can form an ionic compound with let's say the phosphate right and then this would be soluble so be careful what table you're looking at and understanding what the exceptions represent and then our last one on this table is hydroxide so hydroxide is always going to be insoluble again and our exceptions will tell us when it is soluble so here we can see that barium hydroxide will be one of our exceptions so that will be soluble Group 1 cations so we could have lithium for example lithium hydroxide sodium hydroxide right so these will be our soluble exceptions so now let's use this information to write some precipitation reactions our first example is a reaction in which we have sodium chloride aqueous right so that's dissolved in water mixing with silver and nitrate silver nitrate is actually used to test solutions to see if they contain the halides so it will form a precipitate if you have a chloride ion bromide or iodide and so you'll see this type of reaction right the precipitate forming and then falling to the bottom of the test tube so let's write our molecular our complete ionic and net ionic equations for this example what I'd like to do is start with showing what happens when these dissolved ionic compounds dissociate in solution as we learned in a previous video so we know that they'll break up into their constituent ions so this sodium chloride will break up to give us sodium ions and chloride ion and the silver nitrate will also break up into its constituent ions right to give us silver ions and nitrate ions now we talked about how these precipitation reactions are also called double replacement or double displacement it's the idea that our cations and anions are switching Partners so before the sodium and the chloride were together now let's pair the sodium with the nitrate ion and we'll pair the chloride and the silver together so they're just switching their partners when we do that we'll have sodium nitrate and we'll have silver chloride now what we want to do is go to those solubility tables and decide whether our products are going to be soluble or insoluble if they're soluble then we'll get to write the aqueous symbol after them if they are precipitate then we'll write as a solid so if we go back to our tables we'll see that we're looking for silver chloride silver chloride was one of those insoluble exceptions that we had written so this is actually going to be a solid a precipitate the other species that we're looking for is our sodium nitrate we said that sodium is one of those group one cations that is always going to be soluble there are no exceptions so sodium nitrate should be something that dissolves so we can write it as being an aqueous species so this will be our aqueous species and the silver chloride will be our solid so we've written our molecular equation now let's write our complete ionic equation right the product side we know that the silver I'm sorry the sodium nitrate is soluble so it will break apart or dissociate into its ions so we'll have sodium ions and nitrate ions but the silver chloride solid will remain together in the solid form so now we've written our complete ionic equation and if you remember from last time to write the net ionic equation we simply eliminate The Spectator ions so we look for ions that are present on both the reactant and product side and we eliminate them we can see that the sodium ion is present on both sides and the nitrate is present on both sides and so we're left with our net ionic equation we normally start with the cation so I wrote the silver first and then those move on to give us the silver chloride solid let's do another example this reaction yields that lead iodide precipitate the bright yellow that is used in artist pigment was our one of our previous examples this can be generated by reacting potassium iodide and lead nitrate so just as before let's start by writing our reactants for the complete ionic equation we can see that both of these species are aqueous and so we're going to assume that they break apart into their constituent ions so when this potassium iodide dissociates it's going to give me potassium ions and iodide ions and we can see that there is a 2 for my coefficient so I'm also going to make sure to put a 2 in front of each of those ions and now when I think about how the lead nitrate breaks apart into its ions I can see that I will have lead ions and nitrate ions looking at my formula for the lead nitrate I can see that I should have two nitrate ions for every one lead ion so I made sure to put a 2 here for my coefficient so I have dissociated my aqueous reactants and now just as before they're going to switch partners and so my potassium ion is going to reform with the nitrate and then my iodide is going to come together with the lead so let's write those here above right I'm going to have potassium nitrate the spoiler is that this should be aqueous I have two potassiums and two nitrates so I should be able to write a 2 as my coefficient and then when the lead and the iodide come together this is going to give me lead iodide pbi2 and if I go back to look at my solubility table I can see that iodide is normally soluble so here's the iodide ion but one of its exceptions is when it gets together with lead ions so lead iodide is insoluble so here we're going to write it with an S to show that it will be the solid precipitate so this is my molecular equation if I want to complete my complete ionic equation right I'm going to write my product side now so my lead nitrate is going to dissociate to give me the I'm sorry my potassium nitrate is going to dissociate to give me potassium ions and nitrate ions I see that I have two of those so that means I will have two potassium ions as well as two nitrate ions and then finally the lead iodide will stay together in the solid form and so that is our complete ionic equation finally to write our net ionic equation we eliminate The Spectator ions we see that we have potassium on both sides and we also have nitrate on both sides and so rewriting what is left we see that lead 2 plus is going to react with two iodide ions to yield our precipitate which is lead iodide and we make sure to write that it is a solid