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Main content
Current time:0:00Total duration:5:55
AP.Chem:
TRA‑1 (EU)
,
TRA‑1.B (LO)
,
TRA‑1.B.1 (EK)
,
TRA‑1.B.2 (EK)
,
TRA‑1.B.3 (EK)

Video transcript

what we have here is a molecular equation describing the reaction of some sodium chloride dissolved in water plus some silver silver nitrate also dissolved in the water they're going to react to form sodium nitrate still dissolved in water plus solid silver chloride and if you were to look at each of these compounds in their crystalline or solid form before they're dissolved in water they each look like this but once you get dissolved in water and that's what this aqueous form tells us it tells us that each of these compounds are going to get dissolved in water they're no longer going to be in that crystalline form crystalline form instead you're going to have the individual ions disassociating so for example in the case of sodium chloride the sodium is going to disassociate in the water sodium is a positive ion or a cation and so it's going to be attracted to the partially negative oxygen end remember Ock water is a is a polar molecule that's what makes it such a good solvent now the chloride anions similarly are going to dissolve in water because they're going to be attracted to the partially positive hydrogen ends of the water molecules and the same thing is going to be true of the silver nitrate silver the silver ion once it's disassociated is going to be positive and the nitrate is a negative it is an anion now in order to appreciate this and write an equation that better conveys this this is the dissociation of the ions we could instead write the equation like this this makes it a little bit clearer that look the sodium and the chloride aren't going to be necessarily together anymore the sodium is going to dissolve in the water like we have here the chloride is going to dissolve in the water the silver ions are going to dissolve in the water and so is so are the nitrate ions so this makes it a little bit clearer and similarly on this end with the sodium nitrate stays dissolved so we can write it like this with the individual ion's disassociated but the silver chloride is in solid form you could think of it as precipitating out of the solution this is not this does not have a high solubility so it's not going to get dissolved in the water and so we still have it in solid form now you might say well which of these is better well it just depends what you are trying to go for this form up here which we see more typically this is just a standard molecular equation molecular molecular equation can balance form we always want to have our our equations balanced this right over here is known as a complete ionic equation that completes there because we put in all of the ions we're going to compare it to a net ionic equation in a second complete ionic equation sometimes just known as an ionic equation now why is it called that well because we're showing the individual ions and their disassociated in water now what would a net ionic equation be well let's think about that a little bit let me free up some space so we one thing that you notice on both sides of this complete ionic equation you have the same ions that are disassociated in water so for example on the left hand side you have the sodium that's dissolved in water and you also have on the right-hand side sodium dissolved and not in the water it's not if you think about the silver chloride being the thing that's being produced this thing is in ionic form and dissolved form on both sides of this reaction and so you could view it as a spectator and that's actually what it's called it's called a spectator ion spec spectate or ion if you want to think of it in human terms it's kind of out there and watching the reaction happen it's value in this reaction is well it was part of the sodium chloride and it's provided so the sodium chloride is providing the chloride that eventually forms the silver chloride but the sodium is it's just kind of watching similarly you have the nitrate the nitrate is dissolved on the left and the nitrate is dissolved on the right so the nitrate is also a spectator ion so if you want to go from a complete ionic equation to a net ionic equation which really deals with the things that aren't that aren't spectators well you just get rid of the spectator ions so you get rid of that you get rid of that you get rid of that you get rid of that and then you see what is left over well what we have left over is we have some dissolved chloride and we write aqueous to show that it is dissolved plus some dissolved silver plus some dissolved silver once again to show that it's dissolved we write aqueous and if you put those two together you are going to get some solid silver solid silver chloride all right and what's useful about this form it's it's one it's more compact and it's very clear what is actually reacting what is being used to build and you could say hey however you get your chloride into the solution however you get your silver into the solution this is these are the things that are going to react to form the solid instead of using sodium chloride maybe you use potassium chloride and the potassium in that case would be a spectator ion and but either way your net ionic equation would be what we have here