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Current time:0:00Total duration:10:54

Video transcript

I have two water molecules right over here and typically the water molecules as they interact with each other they form these hydrogen bonds that's due to the polarity of the water molecule we've talked a lot about that they slide past each other these hydrogen bonds give them all these neat properties of water but chemistry is much messier than sometimes our diagrams or explanations show there's all sorts of crazy interactions all of these things are bumping into each other in all different ways and not only are the molecules bumping in different ways but any given moment the electrons are jumping around and and on average they might spend more time they might spend more time around the oxygen forming a partially negative charge at that end and then a partially positive charge near the hydrogen's because the hydrogen's are having their electrons hogged away from them in fact this is what forms the hydrogen bonds but there's always constant constantly change there because they're all just jumping around it's all very probabilistic and so you can imagine under just the right conditions one oxygen or one water molecule might just just graze this water molecule in the right way that these electrons that these electrons get close enough to nab to nab this hydrogen but it doesn't NAB the entire hydrogen doesn't nab the nucleus and the electron and a typical hydrogen atom a typical hydrogen atom actually let me draw it a typical hydrogen atom is just a proton is just a proton in the nucleus actually the most typical isotope of hydrogen has no Neutron so it's just a proton in the nucleus and an electron orbiting around it so this right over here is positive actually maybe I'll just do it draw it that way you have a positive proton and then you have a negative electron you have a negative electron orbiting around it actually it's more of a orbital so it's really this electron is jumping all around it but you can imagine these electrons in this covalent bond they were already being these were already being hugged these are already being hugged by this oxygen in fact that's what was forming this partial negative charge over here and a partial positive charge over here so these would be attracted to this partial positive charge remember there you have a partial negative charge over here this is actually it's forming a hydrogen bond and actually could bond to the hydrogen proton while both of these electrons including one of these electrons that used to be part of this hydrogen or you could consider used to be part of that hydrogen are nabbed are nabbed by this oxygen and in this circumstance and I'm not saying that this happens all the time but under just the right conditions this actually can happen and what would result so let me what would result is this thing over here instead of just being a neutral water molecule would look like this so you have your oxygen you have not only your two hydrogen's now you now have a third hydrogen you now have a third hydrogen so you have these two covalent bonds these two covalent bonds this lone pair and now this lone pair which I have circled in blue is now being shared with this hydrogen proton this electron right over here of the hydrogen got nabbed by this oxygen so now you formed another covalent bond and now this character over here he's lost the hydrogen proton but he's kept all of the electrons so this character over here is going to look like this you're going to have your oxygen is still and now it's going to only be bonded to one hydrogen only bonded to one hydrogen has these two original lone pairs these two original lone pairs right over here and then took both of the electrons from this covalent bond and took both of the electrons from this covalent bond and so it has another lone pair so this molecule gained just a proton without getting any electrons so if you do that you're now going to have a net positive charge for this one over here and this molecule over here actually let me let me well let me just write it I want to write a little bit neater and this molecule over here so we have this molecule plus this one this one gained and this one lost a proton without any other changes so it now has a negative charge so just like that you went from two neutral water molecules to two ions and these ions this one over here the one on the left the one that is now h3o h3o h3o and it now has a positive charge positive charge actually I put that o in a different color h3h3 oh it's a positive charge this is called the hydronium ion hydronium hi drone IAM and this one over here that is Oh H - so it's O H oh let me get the colors right Oh H - this is called the hydroxide ion or since its negative you could call it an anion I'll just write hydroxide hi Drock side hydroxide ion right over there so you have this water it's just kind of automatically under the right circumstances this isn't happening a lot but on the right circumstances you could you could have one of the water molecules nabbing just the hydrogen proton from another water molecule and that water molecule is going to keep both of the electrons and then they ionize they have Auto ionized and this phenomenon this is called the autoionization of water let me write that down it's a nice big word auto-ionization auto-ionization of of water and i really want to make it clear what happens this hydrogen over here that you could imagine at first was a proton and electron the typical isotope of hydrogen actually does not have a neutron but then this electron got swiped this electron this electron was part of this bond and it gets swiped away and so all you're left is with this proton and this proton goes to this other water molecule giving that a positive charge and so you might say well how frequently would I find hydronium ions in water well the concentration let me actually draw a little double of water here let's say this is a liter of water this is a liter this is a liter of water the concentration of hydronium in typical water the concentration of h3o the concentration of h3o in typical water you put brackets around something to denote concentration is 1 times 10 to the negative 7 molar and molar this just means moles our leader this is same thing as 1 times 10 to the negative 7 moles moles per liter and now you might be saying well what's the mole well I encourage you to watch the video what a mole is but a mole is a quantity it's like saying a dozen but it's a much larger to 12 of something mole is roughly equal to let me write it a mole is approximately equal to 6.02 times 10 to the 23rd 10 to the 23rd of something and you're typically talking about molecules a mole a mole of a substance means six point ruff approximately 6.022 it actually keeps going times 10 to the 23rd molecules of that thing so you might say 1 times 10 to the negative 7 times 6.02 times 10 to the 23rd that would still get us what we'll see this let me actually let me write down 1 times 10 to the negative 7 moles per liter times times I'll do it this way times 6 I'll just go at 6 since we're going to approximately so approximately 6 times 10 to the 23rd 6 Sept 23rd molecules molecules per mole molecules per mole well these two would cancel out and you would multiply these two numbers you would get 6 times let's see 10 to the negative 7 times 10 to the 23rd that's still going to be 10 to the 16th power molecules per liter molecules per liter so your first reaction is oh my god I'm going to have 6 tie or roughly I'll say roughly approximately 6 times 10 to the 16th molecules of hydronium and this that's a lot we should see it all the time but we have to remind ourselves there's just a lot of molecules of water in there as well in fact a liter of water is roughly so one liter of h2o contains contains approximately 56 56 moles moles of h2o so one way to think about it is I have one I have one time ting about a liter of water I have I'll do it over here I have one times ten to the negative seven moles of moles of h3o for every for every 56 moles for every 56 moles moles of h2o so if you look at this ratio then you start to appreciate the ratio of 1 times 10 the negative 7 to 56 let me let me do it down here so this is the same thing as 1 times 10 to the negative 7 256 is the same thing as let's just multiply both sides times 10 to the set or the numerator and the denominator times 10 to the seventh so if we do that this is the same thing as 1 1 the ratio of hydronium 2 to regular water to a CO 2 o is going to be 1/2 C if I multiply 56 times 10 to the seventh I'm going to have 5 let me get right in that same color I'm going to have 5/6 and I'm going to have I'm going to throw 7 zeros at the end of it let me do that 1 2 3 4 5 6 7 so the ratio of hydronium to regular h2o is one for every 560 million so even though you might say oh wow look we're going to have we have a huge number of molecules of hydronium in this liter of water for every one of them you actually have five hundredths roughly 560 million molecules of h2o so that should give you a pre Shi ation for the fact that this isn't that that typical in fact you're going to see this much more often than you see this over here in fact if you wanted to if you wanted to make these arrows kind of show which direction the equilibrium sits in it's actually much further it's actually much further to the left so we could make this arrow much bigger but it also gives you an appreciation for just how many molecules you have sitting in a liter in a liter of water