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Video transcript

let's say we have some solid sodium chloride so some salt and that right there supposed to be our pile of salt and we're going to put our salt into some water so we have a beaker containing h2o the sodium chloride is going to dissolve in the water so the sodium chloride is our solute and the water will be our solvent so this is the process of dissolution and if you look more closely at sodium chloride right solid sodium chloride is Nayan ik crystal and so it's held together by the ionic bonds right so the sodium cation right with a positive charge is attracted to the chloride anion with a negative charge and so that's holding together our ionic crystal when you put the solid sodium chloride into water remember water is a polar molecule the oxygen is more electronegative than the hydrogen's here's the oxygen gets a partial negative charge and these hydrogen's get a partial positive charge so we have a polar we have a polar molecule here and the negative charge on the oxygen is going to interact with the positive charge on the sodium right opposite charges attract so we have one water molecule here attracted to this sodium cation and this water molecule would do the same right so partial negative charge right attracted to the positive charge on the sodium and so the water molecules are going to pull off the sodium cations and eventually give you this situation over here right so we have the partial negative oxygens right partial negative oxygens are going to are going to interact with the sodium cation all right so the water is a dipole and the sodium cation is an ion so we could call this an ion dipole interaction and so the water molecules break the ionic bonds pull off the sodium cations surround the sodium cation and so we call this process hydration so this is the process of hydration all right where the ion is surrounded and stabilized by a shell of our solvent molecules the same thing would happen with the chloride anion right up here the chloride anion is negatively charged but this time the negative charge would be attracted to the positive part of our polar molecule right so the oxygen is partially negative and this hydrogen here be partially positive and so opposite charges attract the positive charge is going to interact with the negative charge right same for this molecule of water partially positive hydrogen and once again right this interaction is going to pull off that chloride anion and move it into solutions so we have our partial positive hydrogen's right interacting with our and negatively charged chloride anions here so once again we get ion dipole interactions and the chloride anion is surrounded by our water molecules so once again the process of hydration so the end result is each sodium cation is surrounded by water molecules and each chloride anion is surrounded by water molecules so the sodium chloride has dissolved in water we formed a solution an aqueous solution of sodium chloride and the way that you see that written right you would write here we have solid sodium chloride which we put into water our solvent right and the water molecules surrounded our ions so now we have sodium ions in solution so we write an AQ here for aqueous sodium ions and we have chloride anions also in solution so we write an aq here so we have an aqueous solution of sodium chloride the sodium chloride has dissolved in water now let's say we have one beaker that contains a solution of NaCl so an aqueous solution of NaCl has sodium cations in solution and chloride anions in solution let's say we have another beaker that contains a solution of silver nitrate which is AG no.3 so an aqueous solution of silver nitrate means we have silver cations in solution AG + and nitrate anions no.3 minus and now let's say we add the contents of one beaker to the other beaker so let's pour the contents of let's say this beaker in to this beaker so we're combining our two solutions so we would notice a few things we would notice the volume to increase obviously since we're pouring the contents of one into the other and we would also notice a white solid form so a white solid is going to form down here and that white solid forms when the silver cations interact with the chloride anions so we get a solid forming that is silver chloride agcl so we would write AG CL here we put a subscript s indicating that a solid formed this solid is called a precipitate and this solid spontaneously falls out of solution so this is the process of precipitation which is the opposite of dissolution in dissolution we put a solid into water and we formed ions right in precipitation the ions come together to form a solid and that solid spontaneously falls out of solution so silver chloride is our precipitate right we would still have some ions in solution we would still have sodium cations and nitrate anions so in here we would have sodium cations in solution and nitrate anions in solution so we could add them into here we could say we could say nano3 right so aqueous meaning those ions are present in solution let's look in more detail about what's happening with the formation of our precipitate all right we know that we had silver cations in solution all right so here's our silver cation over here and we know that we know that this ion is is being surrounded by water molecules in the process of hydration right so these oxygens are partially negative right here and since opposites attract right there's a force right that's holding that ion in our solution right the forces of hydration same thing for the chloride anion right are the partial positive charge on the hydrogen opposite charges attract right and so the as water molecules are stabilizing the chloride anion in solution but when we pour when we pour those two solutions together right we form our precipitate we form a silver chloride right we form this ionic crystal down here and once again opposite charges attract so the positively charged silver cation is attracted to the negatively charged chloride anion here and since we notice this solid to form the electrostatic attractions of our ionic crystal must be stronger than the forces of hydration so this chloride anion would move into here right and then this silver cation would move into here so the ions come out of solution and a precipitate spontaneously formed so we form our solid silver chloride this is one way to represent what's going on here we could have also drawn out all of the ions right so instead of writing that another way to represent what's happening would be to say a solution of sodium chloride would be sodium cations in solution all right so we write our sodium cations here chloride anions so Cl minus we added to that our solution of silver nitrate which had a silver ions in solution so AG plus and nitrate anion so no.3 minus and we saw we saw a precipitate form alright so we formed AG CL which is our solid so we write AG CL here which is our precipitate and then we also had sodium cations and nitrate anions so we had sodium cations and a plus and we had nitrate anions no.3 minus and so that's that's a lot of writing right so either either one tells you the same amount of information this one down here just shows you all of the ions and really really only some of the ions are reacting right the silver cation and the chloride anion are coming together to form a silver chloride so we could write we could write a net ionic equation showing what's happening to form our precipitate we could show the silver cations here AG plus so we could show our silver cations and our chloride anions combining to form our precipitate AG CL alright so this is the net ionic equation and this is the net ionic equation because some of our ions aren't taking part in this reaction right they're just observing what's happening this sodium cation right is on the left side it's also on the right side as an ion in solution and same thing with the nitrate anion it's over here on the left side as an ion in solution it's over here on the right side as an ion in solution so the sodium cation and the nitrate anion are called spectator ions these are called spectator ions because they're not taking part in what's happening right they're just watching they're watching as the silver chloride precipitates out of solution so that's why we call them spectator ions so this is the idea of precipitation