[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:02.68,Default,,0000,0000,0000,,Let's say I have some weak acid.
Dialogue: 0,0:00:02.70,0:00:04.66,Default,,0000,0000,0000,,I'll call it HA.
Dialogue: 0,0:00:04.68,0:00:07.83,Default,,0000,0000,0000,,A is a place holder for
Dialogue: 0,0:00:07.86,0:00:12.80,Default,,0000,0000,0000,,really a whole set of elements that I could put there.
Dialogue: 0,0:00:12.81,0:00:15.32,Default,,0000,0000,0000,,It could be fluorine, it could be an ammonia molecule.
Dialogue: 0,0:00:15.33,0:00:16.88,Default,,0000,0000,0000,,If you add H it becomes ammonium.
Dialogue: 0,0:00:16.89,0:00:20.07,Default,,0000,0000,0000,,So this isn't any particular element I'm talking about.
Dialogue: 0,0:00:20.08,0:00:23.70,Default,,0000,0000,0000,,This is just kind of a general way of writing an acid.
Dialogue: 0,0:00:23.72,0:00:31.32,Default,,0000,0000,0000,,And let's say it's in equilibrium with, of course,
Dialogue: 0,0:00:31.34,0:00:34.48,Default,,0000,0000,0000,,and you've seen this multiple times, a proton.
Dialogue: 0,0:00:34.50,0:00:37.85,Default,,0000,0000,0000,,And all of this is in an aqueous solution.
Dialogue: 0,0:00:37.87,0:00:42.06,Default,,0000,0000,0000,,Between this proton jumping off of this
Dialogue: 0,0:00:42.07,0:00:43.61,Default,,0000,0000,0000,,and its conjugate base.
Dialogue: 0,0:00:45.08,0:00:48.29,Default,,0000,0000,0000,,And we also could have written a base equilibrium,
Dialogue: 0,0:00:48.31,0:00:50.75,Default,,0000,0000,0000,,where we say the conjugate base could disassociate,
Dialogue: 0,0:00:50.80,0:00:54.96,Default,,0000,0000,0000,,or it could essentially grab a hydrogen from the water
Dialogue: 0,0:00:54.97,0:00:56.23,Default,,0000,0000,0000,,and create OH.
Dialogue: 0,0:00:56.25,0:00:57.67,Default,,0000,0000,0000,,And we've done that multiple times.
Dialogue: 0,0:00:57.70,0:00:59.59,Default,,0000,0000,0000,,But that's not the point of this video.
Dialogue: 0,0:00:59.61,0:01:01.70,Default,,0000,0000,0000,,So let's just think a little bit about
Dialogue: 0,0:01:01.73,0:01:04.54,Default,,0000,0000,0000,,what would happen to this equilibrium
Dialogue: 0,0:01:04.57,0:01:06.62,Default,,0000,0000,0000,,if we were to stress it in some way.
Dialogue: 0,0:01:06.64,0:01:08.09,Default,,0000,0000,0000,,And you can already imagine
Dialogue: 0,0:01:08.12,0:01:11.45,Default,,0000,0000,0000,,that I'm about to touch on Le Chatelier's Principal,
Dialogue: 0,0:01:11.47,0:01:12.74,Default,,0000,0000,0000,,which essentially just says, look,
Dialogue: 0,0:01:12.75,0:01:14.32,Default,,0000,0000,0000,,if you stress an equilibrium in any way,
Dialogue: 0,0:01:14.34,0:01:17.26,Default,,0000,0000,0000,,the equilibrium moves in such a way
Dialogue: 0,0:01:17.30,0:01:18.65,Default,,0000,0000,0000,,to relieve that stress.
Dialogue: 0,0:01:18.67,0:01:22.11,Default,,0000,0000,0000,,So let's say that the stress that I apply to the system
Dialogue: 0,0:01:27.28,0:01:30.23,Default,,0000,0000,0000,,--Let me do a different color.
Dialogue: 0,0:01:30.24,0:01:33.41,Default,,0000,0000,0000,,I'm going to add some strong base.
Dialogue: 0,0:01:33.43,0:01:35.08,Default,,0000,0000,0000,,That's too dark.
Dialogue: 0,0:01:35.10,0:01:39.64,Default,,0000,0000,0000,,I'm going to add some NaOH.
Dialogue: 0,0:01:39.66,0:01:41.49,Default,,0000,0000,0000,,And we know this is a strong base
Dialogue: 0,0:01:41.51,0:01:43.11,Default,,0000,0000,0000,,when you put it in a aqueous solultion,
Dialogue: 0,0:01:43.14,0:01:46.10,Default,,0000,0000,0000,,the sodium part just kind of disassociates,
Dialogue: 0,0:01:46.11,0:01:47.66,Default,,0000,0000,0000,,but the more important thing,
Dialogue: 0,0:01:47.67,0:01:49.22,Default,,0000,0000,0000,,you have all this OH in the solution,
Dialogue: 0,0:01:49.25,0:01:50.89,Default,,0000,0000,0000,,which wants to grab hydrogens away.
Dialogue: 0,0:01:50.90,0:01:53.74,Default,,0000,0000,0000,,So when you add this OH to the solution,
Dialogue: 0,0:01:53.76,0:01:56.71,Default,,0000,0000,0000,,what's going to happen for every mole that you add,
Dialogue: 0,0:01:56.74,0:01:58.77,Default,,0000,0000,0000,,not even just mole,
Dialogue: 0,0:01:58.80,0:02:02.13,Default,,0000,0000,0000,,for every molecule you add of this into the solution,
Dialogue: 0,0:02:02.15,0:02:05.25,Default,,0000,0000,0000,,it's going to eat up a molecule of hydrogen.
Dialogue: 0,0:02:05.27,0:02:06.37,Default,,0000,0000,0000,,Right?
Dialogue: 0,0:02:06.40,0:02:07.45,Default,,0000,0000,0000,,So for example, if you had
Dialogue: 0,0:02:07.47,0:02:10.96,Default,,0000,0000,0000,,1 mole oh hydrogen molecules in your solution
Dialogue: 0,0:02:10.98,0:02:15.78,Default,,0000,0000,0000,,right when you do that,
Dialogue: 0,0:02:15.80,0:02:19.35,Default,,0000,0000,0000,,all this is going to react with all of that.
Dialogue: 0,0:02:19.38,0:02:22.75,Default,,0000,0000,0000,,And the OHs are going to react with the Hs
Dialogue: 0,0:02:22.76,0:02:24.80,Default,,0000,0000,0000,,and form water,
Dialogue: 0,0:02:24.82,0:02:26.47,Default,,0000,0000,0000,,and they'll both just kind of
Dialogue: 0,0:02:26.48,0:02:27.57,Default,,0000,0000,0000,,disappear into the solution.
Dialogue: 0,0:02:27.58,0:02:29.22,Default,,0000,0000,0000,,They didn't disappear, they all turned into water.
Dialogue: 0,0:02:29.25,0:02:32.32,Default,,0000,0000,0000,,And so all of this hydrogen will go away.
Dialogue: 0,0:02:32.34,0:02:34.35,Default,,0000,0000,0000,,Or at least the hydrogen that was initially there.
Dialogue: 0,0:02:34.37,0:02:36.97,Default,,0000,0000,0000,,That 1 mole of hydrogens will disappear.
Dialogue: 0,0:02:37.00,0:02:39.47,Default,,0000,0000,0000,,So what should happen to this reaction?
Dialogue: 0,0:02:39.48,0:02:41.74,Default,,0000,0000,0000,,Well, know this is an equilibrium reaction.
Dialogue: 0,0:02:41.75,0:02:44.08,Default,,0000,0000,0000,,So as these hydrogen disappear,
Dialogue: 0,0:02:46.94,0:02:50.63,Default,,0000,0000,0000,,because this is an equilibrium reaction
Dialogue: 0,0:02:50.66,0:02:52.28,Default,,0000,0000,0000,,or because this is a weak base,
Dialogue: 0,0:02:52.29,0:02:54.37,Default,,0000,0000,0000,,more of this is going to be converted
Dialogue: 0,0:02:54.41,0:02:58.78,Default,,0000,0000,0000,,into these two products
Dialogue: 0,0:02:58.82,0:03:01.30,Default,,0000,0000,0000,,to kind of make up for that loss of hydrogen.
Dialogue: 0,0:03:01.32,0:03:03.37,Default,,0000,0000,0000,,And you can even play with it on the math.
Dialogue: 0,0:03:03.39,0:03:07.07,Default,,0000,0000,0000,,So this hydrogen goes down initially,
Dialogue: 0,0:03:07.09,0:03:10.60,Default,,0000,0000,0000,,and then it starts getting to equilibrium very fast.
Dialogue: 0,0:03:10.61,0:03:12.24,Default,,0000,0000,0000,,But this is going to go down.
Dialogue: 0,0:03:12.26,0:03:14.72,Default,,0000,0000,0000,,This is going to go up.
Dialogue: 0,0:03:14.74,0:03:17.56,Default,,0000,0000,0000,,And then this is going to go down less.
Dialogue: 0,0:03:17.58,0:03:20.09,Default,,0000,0000,0000,,Because sure, when you put the sodium hydroxide there,
Dialogue: 0,0:03:20.11,0:03:21.97,Default,,0000,0000,0000,,it just ate up all of the hydrogens.
Dialogue: 0,0:03:21.99,0:03:23.60,Default,,0000,0000,0000,,But then you have this
Dialogue: 0,0:03:23.62,0:03:24.75,Default,,0000,0000,0000,,-- you can kind of view as
Dialogue: 0,0:03:24.77,0:03:28.46,Default,,0000,0000,0000,,the spare hydrogen capacity here to produce hydrogens.
Dialogue: 0,0:03:28.48,0:03:29.75,Default,,0000,0000,0000,,And when these disappear,
Dialogue: 0,0:03:29.78,0:03:31.98,Default,,0000,0000,0000,,this weak base will disassociate more.
Dialogue: 0,0:03:32.00,0:03:34.70,Default,,0000,0000,0000,,The equilibrium we'll move more in this direction.
Dialogue: 0,0:03:34.72,0:03:38.57,Default,,0000,0000,0000,,So immediately, this will eat all of that.
Dialogue: 0,0:03:38.59,0:03:40.49,Default,,0000,0000,0000,,But then when the equilibrium moves in that direction,
Dialogue: 0,0:03:40.51,0:03:42.58,Default,,0000,0000,0000,,a lot of the hydrogen will be replaced.
Dialogue: 0,0:03:42.60,0:03:44.68,Default,,0000,0000,0000,,So if you think about what's happening,
Dialogue: 0,0:03:44.70,0:03:48.61,Default,,0000,0000,0000,,if I just threw this sodium hydroxide in water.
Dialogue: 0,0:03:48.63,0:03:54.33,Default,,0000,0000,0000,,So if I just did NaOH in an aqueous solution
Dialogue: 0,0:03:54.35,0:03:55.69,Default,,0000,0000,0000,,so that's just throwing it in water
Dialogue: 0,0:03:55.71,0:03:57.88,Default,,0000,0000,0000,,-- that disassociates completely
Dialogue: 0,0:03:57.90,0:04:05.73,Default,,0000,0000,0000,,into the sodium cation and hydroxide anion.
Dialogue: 0,0:04:05.75,0:04:09.50,Default,,0000,0000,0000,,So you all of a sudden immediately
Dialogue: 0,0:04:09.52,0:04:12.00,Default,,0000,0000,0000,,increase the quantity of OHs
Dialogue: 0,0:04:12.01,0:04:15.06,Default,,0000,0000,0000,,by essentially the number of moles of
Dialogue: 0,0:04:15.08,0:04:16.69,Default,,0000,0000,0000,,sodium hydroxide you're adding,
Dialogue: 0,0:04:16.71,0:04:20.28,Default,,0000,0000,0000,,and you'd immediately increase the pH, right?
Dialogue: 0,0:04:20.30,0:04:22.94,Default,,0000,0000,0000,,Remember. When you increase the amount of OH,
Dialogue: 0,0:04:22.95,0:04:27.78,Default,,0000,0000,0000,,you would decrease the pOH, right?
Dialogue: 0,0:04:27.80,0:04:29.92,Default,,0000,0000,0000,,And that's just because it's the negative log.
Dialogue: 0,0:04:29.96,0:04:34.28,Default,,0000,0000,0000,,So if you increase OH, you're decreasing pOH,
Dialogue: 0,0:04:34.30,0:04:36.65,Default,,0000,0000,0000,,and you're increasing pH.
Dialogue: 0,0:04:36.68,0:04:42.28,Default,,0000,0000,0000,,And just think OH-- you're making it more basic.
Dialogue: 0,0:04:42.29,0:04:46.45,Default,,0000,0000,0000,,And a high pH is also very basic.
Dialogue: 0,0:04:46.47,0:04:49.20,Default,,0000,0000,0000,,If you have a mole of this, you end up with a pH of 14.
Dialogue: 0,0:04:49.22,0:04:51.54,Default,,0000,0000,0000,,And if you had a strong acid, not a strong base,
Dialogue: 0,0:04:51.56,0:04:53.15,Default,,0000,0000,0000,,you would end up with a pH of 0.
Dialogue: 0,0:04:53.18,0:04:56.01,Default,,0000,0000,0000,,Hopefully you're getting a little bit familiar
Dialogue: 0,0:04:56.03,0:04:57.48,Default,,0000,0000,0000,,with that concept right now,
Dialogue: 0,0:04:57.50,0:04:59.47,Default,,0000,0000,0000,,but if it confuses you,
Dialogue: 0,0:04:59.49,0:05:01.20,Default,,0000,0000,0000,,just play around with the logs a little bit
Dialogue: 0,0:05:01.20,0:05:02.21,Default,,0000,0000,0000,,and you'll eventually get it.
Dialogue: 0,0:05:02.23,0:05:03.75,Default,,0000,0000,0000,,But just to get back to the point,
Dialogue: 0,0:05:03.77,0:05:06.31,Default,,0000,0000,0000,,if you just did this in water,
Dialogue: 0,0:05:06.33,0:05:08.27,Default,,0000,0000,0000,,you immediately get a super high pH
Dialogue: 0,0:05:08.29,0:05:11.12,Default,,0000,0000,0000,,because the OH concentration goes through the roof.
Dialogue: 0,0:05:11.14,0:05:12.25,Default,,0000,0000,0000,,But if you do it here
Dialogue: 0,0:05:12.26,0:05:16.08,Default,,0000,0000,0000,,--if you apply the sodium hydroxide to this solution,
Dialogue: 0,0:05:16.10,0:05:17.47,Default,,0000,0000,0000,,the solution that contains
Dialogue: 0,0:05:17.49,0:05:20.75,Default,,0000,0000,0000,,a weak acid and it's conjugate base,
Dialogue: 0,0:05:20.77,0:05:23.84,Default,,0000,0000,0000,,the weak acid and its conjugate base,
Dialogue: 0,0:05:23.86,0:05:25.22,Default,,0000,0000,0000,,what happens?
Dialogue: 0,0:05:25.23,0:05:28.29,Default,,0000,0000,0000,,Sure, it immediately reacts with all of this hydrogen
Dialogue: 0,0:05:28.30,0:05:29.44,Default,,0000,0000,0000,,and eats it all up.
Dialogue: 0,0:05:29.47,0:05:31.11,Default,,0000,0000,0000,,And then you have this extras supply here
Dialogue: 0,0:05:31.13,0:05:33.39,Default,,0000,0000,0000,,that just keeps providing more and more hydrogens.
Dialogue: 0,0:05:33.41,0:05:34.91,Default,,0000,0000,0000,,And it'll make up a lot of the loss.
Dialogue: 0,0:05:34.92,0:05:38.41,Default,,0000,0000,0000,,So essentially, the stress won't be as bad.
Dialogue: 0,0:05:38.43,0:05:42.17,Default,,0000,0000,0000,,And over here, you dramatically increase the pH
Dialogue: 0,0:05:42.20,0:05:43.99,Default,,0000,0000,0000,,when you just throw it on water.
Dialogue: 0,0:05:44.00,0:05:46.63,Default,,0000,0000,0000,,Here, you're going to increase the pH by a lot less.
Dialogue: 0,0:05:46.64,0:05:50.43,Default,,0000,0000,0000,,And in future videos, we'll actually do the math of
Dialogue: 0,0:05:50.45,0:05:52.68,Default,,0000,0000,0000,,how much less it's increasing the pH.
Dialogue: 0,0:05:52.70,0:05:54.35,Default,,0000,0000,0000,,But the way you could think about it is,
Dialogue: 0,0:05:54.37,0:05:57.00,Default,,0000,0000,0000,,this is kind of a shock absorber for pH.
Dialogue: 0,0:05:57.02,0:05:59.33,Default,,0000,0000,0000,,Even though you threw this strong based
Dialogue: 0,0:05:59.35,0:06:01.05,Default,,0000,0000,0000,,into this solution,
Dialogue: 0,0:06:01.07,0:06:02.77,Default,,0000,0000,0000,,it didn't increase the pH
Dialogue: 0,0:06:02.79,0:06:04.46,Default,,0000,0000,0000,,as much as you would have expected.
Dialogue: 0,0:06:04.47,0:06:05.71,Default,,0000,0000,0000,,And you can make it the other way.
Dialogue: 0,0:06:05.73,0:06:07.93,Default,,0000,0000,0000,,If I just wrote this exact same reaction
Dialogue: 0,0:06:07.94,0:06:09.05,Default,,0000,0000,0000,,as a basic reaction
Dialogue: 0,0:06:09.06,0:06:12.12,Default,,0000,0000,0000,,--and remember, this is the same thing.
Dialogue: 0,0:06:12.14,0:06:15.65,Default,,0000,0000,0000,,So if I just wrote this as, A minus
Dialogue: 0,0:06:15.67,0:06:17.49,Default,,0000,0000,0000,,--so I just wrote its conjugate base--
Dialogue: 0,0:06:17.51,0:06:22.04,Default,,0000,0000,0000,,is in equilibrium with the conjugate base
Dialogue: 0,0:06:22.06,0:06:27.62,Default,,0000,0000,0000,,grabbing some water from the surrounding aqueous solution.
Dialogue: 0,0:06:27.65,0:06:29.10,Default,,0000,0000,0000,,Everything we're dealing with right now
Dialogue: 0,0:06:29.12,0:06:30.17,Default,,0000,0000,0000,,is an aqueous solution.
Dialogue: 0,0:06:30.19,0:06:32.57,Default,,0000,0000,0000,,And of course that water that it grabbed from
Dialogue: 0,0:06:32.58,0:06:33.74,Default,,0000,0000,0000,,is not going to be an OH.
Dialogue: 0,0:06:33.75,0:06:36.73,Default,,0000,0000,0000,,Remember, are just equivalent reactions.
Dialogue: 0,0:06:36.75,0:06:38.99,Default,,0000,0000,0000,,Here, I'm writing it as an acidic reaction.
Dialogue: 0,0:06:39.01,0:06:40.64,Default,,0000,0000,0000,,Here, I'm writing it is a basic reaction.
Dialogue: 0,0:06:40.66,0:06:41.70,Default,,0000,0000,0000,,But they're equivalent.
Dialogue: 0,0:06:41.72,0:06:42.75,Default,,0000,0000,0000,,Now.
Dialogue: 0,0:06:42.77,0:06:46.47,Default,,0000,0000,0000,,If you were to add a strong acid to the solution,
Dialogue: 0,0:06:46.48,0:06:47.65,Default,,0000,0000,0000,,what would happen?
Dialogue: 0,0:06:47.67,0:06:50.83,Default,,0000,0000,0000,,So if I were to throw hydrogen chloride into this.
Dialogue: 0,0:06:50.85,0:06:53.88,Default,,0000,0000,0000,,Well hydrogen chloride, if you just throw it
Dialogue: 0,0:06:53.89,0:06:56.94,Default,,0000,0000,0000,,into straight up water without the solution,
Dialogue: 0,0:06:56.96,0:06:58.48,Default,,0000,0000,0000,,it would completely disassociate into
Dialogue: 0,0:06:58.51,0:07:04.81,Default,,0000,0000,0000,,a bunch of hydrogens and a bunch of chlorine anions.
Dialogue: 0,0:07:04.83,0:07:07.19,Default,,0000,0000,0000,,And it would immediately make it very acidic.
Dialogue: 0,0:07:07.21,0:07:09.00,Default,,0000,0000,0000,,You would get to a very low pH.
Dialogue: 0,0:07:09.02,0:07:10.87,Default,,0000,0000,0000,,If you had a mole of this
Dialogue: 0,0:07:10.89,0:07:12.87,Default,,0000,0000,0000,,--if your concentration was 1 molar,
Dialogue: 0,0:07:12.90,0:07:15.05,Default,,0000,0000,0000,,then this will go to a pH of 0.
Dialogue: 0,0:07:15.07,0:07:17.79,Default,,0000,0000,0000,,But what happens if you add hydrochloric acid to
Dialogue: 0,0:07:17.81,0:07:20.68,Default,,0000,0000,0000,,this solution right here?
Dialogue: 0,0:07:20.69,0:07:22.34,Default,,0000,0000,0000,,This one that has this weak base
Dialogue: 0,0:07:22.37,0:07:24.54,Default,,0000,0000,0000,,and its conjugate weak acid?
Dialogue: 0,0:07:24.55,0:07:28.78,Default,,0000,0000,0000,,Well, all of these hydrogen protons that
Dialogue: 0,0:07:28.80,0:07:30.34,Default,,0000,0000,0000,,disassociate from the hydrochloric acid
Dialogue: 0,0:07:30.35,0:07:33.00,Default,,0000,0000,0000,,are all going to react with these OHs you have here.
Dialogue: 0,0:07:33.02,0:07:35.52,Default,,0000,0000,0000,,And they're just going to cancel each other out.
Dialogue: 0,0:07:35.54,0:07:38.00,Default,,0000,0000,0000,,They're just going to merge with these and turn into water
Dialogue: 0,0:07:38.02,0:07:39.81,Default,,0000,0000,0000,,and become part of the aqueous solution.
Dialogue: 0,0:07:39.83,0:07:43.08,Default,,0000,0000,0000,,So this, the OHs are going to go down initially,
Dialogue: 0,0:07:43.10,0:07:46.92,Default,,0000,0000,0000,,but then you have this reserve of weak base here.
Dialogue: 0,0:07:46.94,0:07:49.38,Default,,0000,0000,0000,,And Le Chatelier's Principal tells us.
Dialogue: 0,0:07:49.39,0:07:51.45,Default,,0000,0000,0000,,Look, if we have a stressor
Dialogue: 0,0:07:51.46,0:07:55.27,Default,,0000,0000,0000,,that is decreasing our overall concentration of OH,
Dialogue: 0,0:07:55.29,0:07:57.29,Default,,0000,0000,0000,,then the reaction is going to
Dialogue: 0,0:07:57.30,0:08:00.35,Default,,0000,0000,0000,,move in the direction that relieves that stress.
Dialogue: 0,0:08:00.36,0:08:02.70,Default,,0000,0000,0000,,So the reaction is going to go in that direction.
Dialogue: 0,0:08:02.72,0:08:05.22,Default,,0000,0000,0000,,So you're going to have more of our weak base
Dialogue: 0,0:08:05.24,0:08:07.72,Default,,0000,0000,0000,,turning into a weak acid and producing more OH.
Dialogue: 0,0:08:07.75,0:08:12.56,Default,,0000,0000,0000,,So the pH won't go down as much as you would expect
Dialogue: 0,0:08:12.57,0:08:13.99,Default,,0000,0000,0000,,if you just threw this in water.
Dialogue: 0,0:08:14.01,0:08:15.75,Default,,0000,0000,0000,,This is going to lower the pH,
Dialogue: 0,0:08:15.76,0:08:18.29,Default,,0000,0000,0000,,but then you have more OH that could be produced as
Dialogue: 0,0:08:18.30,0:08:21.02,Default,,0000,0000,0000,,this guy grabs more and more hydrogens from the water.
Dialogue: 0,0:08:21.04,0:08:23.48,Default,,0000,0000,0000,,So the way to think about it is it's kind of like
Dialogue: 0,0:08:23.50,0:08:26.65,Default,,0000,0000,0000,,a cushion or a spring in terms of what
Dialogue: 0,0:08:26.67,0:08:30.96,Default,,0000,0000,0000,,a strong acid or base could do to the solution.
Dialogue: 0,0:08:30.97,0:08:33.52,Default,,0000,0000,0000,,And that's why it's called a buffer.
Dialogue: 0,0:08:38.65,0:08:41.66,Default,,0000,0000,0000,,Because it provides a cushion on acidity.
Dialogue: 0,0:08:41.68,0:08:44.09,Default,,0000,0000,0000,,If you add a strong base to water,
Dialogue: 0,0:08:44.11,0:08:46.82,Default,,0000,0000,0000,,you immediately increase its pH.
Dialogue: 0,0:08:46.84,0:08:49.05,Default,,0000,0000,0000,,Or you decrease its acidity dramatically.
Dialogue: 0,0:08:49.07,0:08:51.27,Default,,0000,0000,0000,,But if you add a strong base to a buffer,
Dialogue: 0,0:08:51.29,0:08:53.80,Default,,0000,0000,0000,,because of Le Chatelier's Principal,
Dialogue: 0,0:08:53.81,0:08:56.42,Default,,0000,0000,0000,,essentially, you're not going to affect the pH as much.
Dialogue: 0,0:08:56.44,0:08:57.47,Default,,0000,0000,0000,,Same thing.
Dialogue: 0,0:08:57.49,0:08:59.72,Default,,0000,0000,0000,,If you add and acid to that same buffer,
Dialogue: 0,0:08:59.73,0:09:01.81,Default,,0000,0000,0000,,it's not going to affect the pH
Dialogue: 0,0:09:01.82,0:09:03.51,Default,,0000,0000,0000,,as much as you would have expected
Dialogue: 0,0:09:03.53,0:09:05.22,Default,,0000,0000,0000,,if you had thrown that acid in water
Dialogue: 0,0:09:05.23,0:09:07.99,Default,,0000,0000,0000,,because the equilibrium reaction can always
Dialogue: 0,0:09:08.00,0:09:11.51,Default,,0000,0000,0000,,kind of refill the amount of OH that you lost
Dialogue: 0,0:09:11.53,0:09:13.00,Default,,0000,0000,0000,,if you're adding acid,
Dialogue: 0,0:09:13.02,0:09:16.01,Default,,0000,0000,0000,,or it can refill the amount of hydrogen you lost
Dialogue: 0,0:09:16.03,0:09:17.86,Default,,0000,0000,0000,,if you're adding a base.
Dialogue: 0,0:09:17.88,0:09:20.14,Default,,0000,0000,0000,,And that's why it's called buffer. It provides a cushion.
Dialogue: 0,0:09:20.15,0:09:23.32,Default,,0000,0000,0000,,So it give some stability to the solution's pH.
Dialogue: 0,0:09:23.34,0:09:30.63,Default,,0000,0000,0000,,The definition of a buffer is
Dialogue: 0,0:09:30.65,0:09:34.45,Default,,0000,0000,0000,,just a solution of a weak acid in equilibrium
Dialogue: 0,0:09:34.47,0:09:36.37,Default,,0000,0000,0000,,with its conjugate weak base.
Dialogue: 0,0:09:36.40,0:09:38.45,Default,,0000,0000,0000,,That's what a buffer is, and it's called a buffer
Dialogue: 0,0:09:38.48,0:09:40.92,Default,,0000,0000,0000,,because it provides you this kind of cushion of pH.
Dialogue: 0,0:09:40.96,0:09:43.30,Default,,0000,0000,0000,,It's kind of a stress absorber,
Dialogue: 0,0:09:43.32,0:09:46.56,Default,,0000,0000,0000,,or a shock absorber for the acidity of a solution.
Dialogue: 0,0:09:46.59,0:09:48.54,Default,,0000,0000,0000,,Now, with that said,
Dialogue: 0,0:09:48.57,0:09:51.39,Default,,0000,0000,0000,,let's explore a little bit the math of a buffer,
Dialogue: 0,0:09:51.40,0:09:54.39,Default,,0000,0000,0000,,which is really just the math of a weak acid.
Dialogue: 0,0:09:54.41,0:09:57.78,Default,,0000,0000,0000,,So if we rewrite the equation again,
Dialogue: 0,0:09:57.80,0:10:01.78,Default,,0000,0000,0000,,so HA is in equilibrium.
Dialogue: 0,0:10:01.80,0:10:04.79,Default,,0000,0000,0000,,Everything's in an aqueous solution.
Dialogue: 0,0:10:04.81,0:10:10.16,Default,,0000,0000,0000,,With hydrogen and its conjugate base.
Dialogue: 0,0:10:10.18,0:10:15.02,Default,,0000,0000,0000,,We know that there's an equilibrium constant for this.
Dialogue: 0,0:10:15.04,0:10:17.42,Default,,0000,0000,0000,,We've done many videos on that.
Dialogue: 0,0:10:17.44,0:10:20.06,Default,,0000,0000,0000,,The equilibrium constant here is equal to
Dialogue: 0,0:10:20.08,0:10:23.65,Default,,0000,0000,0000,,the concentration of our hydrogen proton
Dialogue: 0,0:10:23.66,0:10:26.73,Default,,0000,0000,0000,,times the concentration of our conjugate base.
Dialogue: 0,0:10:26.75,0:10:29.89,Default,,0000,0000,0000,,When I say concentration, I'm talking molarity.
Dialogue: 0,0:10:29.90,0:10:32.88,Default,,0000,0000,0000,,Moles per liter divided by
Dialogue: 0,0:10:32.90,0:10:34.53,Default,,0000,0000,0000,,the concentration of our weak acid.
Dialogue: 0,0:10:34.55,0:10:36.51,Default,,0000,0000,0000,,Now.
Dialogue: 0,0:10:36.53,0:10:43.95,Default,,0000,0000,0000,,Let's solve for hydrogen concentration.
Dialogue: 0,0:10:43.97,0:10:45.89,Default,,0000,0000,0000,,Because what I want to do is
Dialogue: 0,0:10:45.92,0:10:47.04,Default,,0000,0000,0000,,I want to figure out a formula,
Dialogue: 0,0:10:47.06,0:10:49.84,Default,,0000,0000,0000,,and we'll call it the Hendersen-Hasselbalch Formula,
Dialogue: 0,0:10:49.86,0:10:52.19,Default,,0000,0000,0000,,which a lot of books want you to memorize,
Dialogue: 0,0:10:52.20,0:10:53.63,Default,,0000,0000,0000,,which I don't think you should.
Dialogue: 0,0:10:53.64,0:10:54.77,Default,,0000,0000,0000,,I think you should always just be able to
Dialogue: 0,0:10:54.79,0:10:57.71,Default,,0000,0000,0000,,go from this kind of basic assumption and get to it.
Dialogue: 0,0:10:57.72,0:10:59.41,Default,,0000,0000,0000,,But let's solve for the hydrogen
Dialogue: 0,0:10:59.42,0:11:00.96,Default,,0000,0000,0000,,so we can figure out a relationship
Dialogue: 0,0:11:00.98,0:11:03.58,Default,,0000,0000,0000,,between pH and all the other stuff that's in this formula.
Dialogue: 0,0:11:03.59,0:11:06.27,Default,,0000,0000,0000,,So, if we want to solve for hydrogen,
Dialogue: 0,0:11:06.29,0:11:07.54,Default,,0000,0000,0000,,we can multiply both sides
Dialogue: 0,0:11:07.56,0:11:10.39,Default,,0000,0000,0000,,by the reciprocal of this right here.
Dialogue: 0,0:11:10.40,0:11:14.05,Default,,0000,0000,0000,,And you get hydrogen concentration.
Dialogue: 0,0:11:14.06,0:11:19.01,Default,,0000,0000,0000,,Ka times
Dialogue: 0,0:11:19.02,0:11:21.47,Default,,0000,0000,0000,,--I'm multiplying both sides times a reciprocal of that.
Dialogue: 0,0:11:21.48,0:11:24.99,Default,,0000,0000,0000,,So times the concentration of our weak acid
Dialogue: 0,0:11:25.01,0:11:28.11,Default,,0000,0000,0000,,divided by the concentration of our weak base
Dialogue: 0,0:11:28.13,0:11:34.42,Default,,0000,0000,0000,,is equal to our concentration of our hydrogen.
Dialogue: 0,0:11:34.43,0:11:36.27,Default,,0000,0000,0000,,Fair enough.
Dialogue: 0,0:11:36.29,0:11:37.31,Default,,0000,0000,0000,,Now.
Dialogue: 0,0:11:37.32,0:11:39.27,Default,,0000,0000,0000,,Let's take the negative log of both sides.
Dialogue: 0,0:11:39.28,0:11:47.84,Default,,0000,0000,0000,,So the negative log of all of that stuff,
Dialogue: 0,0:11:47.85,0:11:51.86,Default,,0000,0000,0000,,of your acidic equilibrium constant,
Dialogue: 0,0:11:51.88,0:12:03.03,Default,,0000,0000,0000,,times HA, our weak acid divided by our weak base,
Dialogue: 0,0:12:03.05,0:12:07.04,Default,,0000,0000,0000,,is equal to the negative log of
Dialogue: 0,0:12:07.07,0:12:08.29,Default,,0000,0000,0000,,our hydrogen concentration.
Dialogue: 0,0:12:08.30,0:12:10.03,Default,,0000,0000,0000,,Which is just our pH, right?
Dialogue: 0,0:12:10.05,0:12:13.14,Default,,0000,0000,0000,,Negative log of hydrogen concentration is
Dialogue: 0,0:12:13.16,0:12:15.46,Default,,0000,0000,0000,,--that's the definition of pH.
Dialogue: 0,0:12:15.48,0:12:18.31,Default,,0000,0000,0000,,I'll write the p and the H in different colors.
Dialogue: 0,0:12:18.35,0:12:20.06,Default,,0000,0000,0000,,You know a p just means negative log.
Dialogue: 0,0:12:20.07,0:12:23.35,Default,,0000,0000,0000,,Minus log. That's all. Base 10.
Dialogue: 0,0:12:23.39,0:12:25.73,Default,,0000,0000,0000,,Let's see if we can simplify this any more.
Dialogue: 0,0:12:25.76,0:12:29.61,Default,,0000,0000,0000,,So our logarithmic properties.
Dialogue: 0,0:12:29.64,0:12:34.00,Default,,0000,0000,0000,,We know that when you take the log of something
Dialogue: 0,0:12:34.02,0:12:35.07,Default,,0000,0000,0000,,and you multiply it,
Dialogue: 0,0:12:35.09,0:12:36.82,Default,,0000,0000,0000,,that's the same thing as taking the log of this
Dialogue: 0,0:12:36.85,0:12:38.13,Default,,0000,0000,0000,,plus the log of that.
Dialogue: 0,0:12:38.15,0:12:46.35,Default,,0000,0000,0000,,So this can to be simplified to minus log of our Ka minus
Dialogue: 0,0:12:46.38,0:12:57.21,Default,,0000,0000,0000,,the log of our weak acid concentration divided by
Dialogue: 0,0:12:57.22,0:12:58.87,Default,,0000,0000,0000,,its conjugate base concentration.
Dialogue: 0,0:12:58.89,0:13:03.27,Default,,0000,0000,0000,,Is equal to the pH.
Dialogue: 0,0:13:03.28,0:13:08.23,Default,,0000,0000,0000,,Now, this is just the pKa of our weak acid,
Dialogue: 0,0:13:08.25,0:13:09.94,Default,,0000,0000,0000,,which is just the negative log of
Dialogue: 0,0:13:09.95,0:13:13.16,Default,,0000,0000,0000,,its equilibrium constant.
Dialogue: 0,0:13:13.17,0:13:14.49,Default,,0000,0000,0000,,So this is just the pKa.
Dialogue: 0,0:13:14.52,0:13:18.59,Default,,0000,0000,0000,,And the minus log of HA over A.
Dialogue: 0,0:13:18.60,0:13:21.69,Default,,0000,0000,0000,,What we can do is we could make this a plus,
Dialogue: 0,0:13:21.71,0:13:24.35,Default,,0000,0000,0000,,and just take this to the minus 1 power. Right?
Dialogue: 0,0:13:24.37,0:13:25.93,Default,,0000,0000,0000,,That's just another logarithm property,
Dialogue: 0,0:13:25.95,0:13:27.73,Default,,0000,0000,0000,,and you can review the logarithm videos
Dialogue: 0,0:13:27.76,0:13:28.78,Default,,0000,0000,0000,,if that confused you.
Dialogue: 0,0:13:28.81,0:13:31.31,Default,,0000,0000,0000,,And this to the minus 1 power just means invert this.
Dialogue: 0,0:13:31.33,0:13:32.34,Default,,0000,0000,0000,,So we could say,
Dialogue: 0,0:13:32.36,0:13:37.39,Default,,0000,0000,0000,,plus the logarithm of our conjugate base concentration
Dialogue: 0,0:13:37.40,0:13:40.23,Default,,0000,0000,0000,,divided by the weak acid concentration
Dialogue: 0,0:13:40.24,0:13:43.09,Default,,0000,0000,0000,,is equal to the pH.
Dialogue: 0,0:13:43.11,0:13:44.54,Default,,0000,0000,0000,,And this right here,
Dialogue: 0,0:13:44.56,0:13:47.11,Default,,0000,0000,0000,,this is called the Hendersen-Hasselbalch Equation.
Dialogue: 0,0:13:47.12,0:13:51.68,Default,,0000,0000,0000,,And I really encourage you not to memorize it.
Dialogue: 0,0:13:51.70,0:13:54.27,Default,,0000,0000,0000,,Because if you do attempt to memorize it,
Dialogue: 0,0:13:54.28,0:13:56.98,Default,,0000,0000,0000,,within a few hours, you're going to forget
Dialogue: 0,0:13:57.00,0:13:58.47,Default,,0000,0000,0000,,whether this was a plus over here.
Dialogue: 0,0:13:58.48,0:13:59.88,Default,,0000,0000,0000,,You're going to forget this,
Dialogue: 0,0:13:59.90,0:14:01.85,Default,,0000,0000,0000,,and you're going to forget whether you
Dialogue: 0,0:14:01.87,0:14:03.36,Default,,0000,0000,0000,,put the A minus or the HA
Dialogue: 0,0:14:03.39,0:14:04.75,Default,,0000,0000,0000,,on the numerator or the demoninator,
Dialogue: 0,0:14:04.77,0:14:06.04,Default,,0000,0000,0000,,and if you forget that, it's fatal.
Dialogue: 0,0:14:06.07,0:14:07.80,Default,,0000,0000,0000,,The better thing is to just start
Dialogue: 0,0:14:07.82,0:14:10.25,Default,,0000,0000,0000,,from your base assumptions. And trust me.
Dialogue: 0,0:14:10.27,0:14:11.61,Default,,0000,0000,0000,,It took me a couple minutes to do it,
Dialogue: 0,0:14:11.63,0:14:13.24,Default,,0000,0000,0000,,but if you just do it really fast on paper,
Dialogue: 0,0:14:13.27,0:14:14.94,Default,,0000,0000,0000,,you don't have to talk it through the way I did
Dialogue: 0,0:14:14.97,0:14:18.06,Default,,0000,0000,0000,,--it'll take in no time at all to come to this equation.
Dialogue: 0,0:14:18.07,0:14:19.41,Default,,0000,0000,0000,,It's much better than memorizing it,
Dialogue: 0,0:14:19.43,0:14:22.35,Default,,0000,0000,0000,,and you won't forget it when you're 30 years old.
Dialogue: 0,0:14:22.37,0:14:24.75,Default,,0000,0000,0000,,But what's useful about this?
Dialogue: 0,0:14:24.76,0:14:28.83,Default,,0000,0000,0000,,Well, it immediately relates pH to our pKa,
Dialogue: 0,0:14:28.84,0:14:31.37,Default,,0000,0000,0000,,and this is a constant, right, for an equilibrium?
Dialogue: 0,0:14:31.40,0:14:35.12,Default,,0000,0000,0000,,Plus the log of the ratios between the acid
Dialogue: 0,0:14:35.14,0:14:37.05,Default,,0000,0000,0000,,and the conjugate base.
Dialogue: 0,0:14:37.08,0:14:40.41,Default,,0000,0000,0000,,So the more conjugate base I have,
Dialogue: 0,0:14:40.43,0:14:42.59,Default,,0000,0000,0000,,and the less acid I have,
Dialogue: 0,0:14:42.61,0:14:45.47,Default,,0000,0000,0000,,the more my pH is going to increase. Right?
Dialogue: 0,0:14:45.49,0:14:47.77,Default,,0000,0000,0000,,If this goes up and this is going down,
Dialogue: 0,0:14:47.79,0:14:49.10,Default,,0000,0000,0000,,my pH is going to increase. Which makes sense
Dialogue: 0,0:14:49.11,0:14:51.27,Default,,0000,0000,0000,,because I have more base in the solution.
Dialogue: 0,0:14:51.28,0:14:52.87,Default,,0000,0000,0000,,And if I have the inverse of that,
Dialogue: 0,0:14:52.90,0:14:54.70,Default,,0000,0000,0000,,might be just going...