0:00:00.000,0:00:00.000 0:00:00.000,0:00:04.087 Sal: We know that if we leave[br]water to its own devices-- so 0:00:04.087,0:00:08.000 you have some H2O-- that it's[br]an equilibrium with the 0:00:08.000,0:00:10.024 autoionized version of itself. 0:00:10.024,0:00:13.084 So a little bit of it will turn[br]into some hydrogen ions, 0:00:13.084,0:00:16.000 and we know that this really[br]takes the form hydronium. 0:00:16.000,0:00:18.039 That these attach themselves[br]to other water molecules. 0:00:18.039,0:00:21.057 And it could be H3O, but[br]we'll just write it 0:00:21.057,0:00:23.064 as a hydrogen ion. 0:00:23.064,0:00:26.023 Which is really just a[br]free-floating proton. 0:00:26.023,0:00:29.087 Plus hydroxide ion. 0:00:29.087,0:00:34.047 And we also know that in kind of[br]an equilibrium state at 25 0:00:34.047,0:00:36.085 degrees Celsius. 0:00:36.085,0:00:39.042 And remember, equilibrium[br]constants and equilibrium 0:00:39.042,0:00:42.003 reactions are only dependent[br]on the temperature. 0:00:42.003,0:00:43.078 Nothing else. 0:00:43.078,0:00:46.047 For a given molecule,[br]of course. 0:00:46.047,0:00:48.090 So 25 degrees Celsius. 0:00:48.090,0:00:51.064 And we also know, we did this[br]two videos ago, that the 0:00:51.064,0:00:54.040 equilibrium constant-- as[br]a review, that's the 0:00:54.040,0:01:01.099 concentration of the products[br]divided by the concentration 0:01:01.099,0:01:03.022 of the reactants. 0:01:03.022,0:01:05.027 But the reactant in this[br]case is just water. 0:01:05.027,0:01:06.059 It's the actual solvent. 0:01:06.059,0:01:09.065 And if the reactant is what[br]you're-- it's everywhere. 0:01:09.065,0:01:11.078 So if you just go back to that[br]intuition example, the 0:01:11.078,0:01:13.087 probability of finding[br]it is 1. 0:01:13.087,0:01:17.029 So it's just always there,[br]so you don't included it. 0:01:17.029,0:01:19.067 So you can just say divided by[br]1 or whatever, and this is 0:01:19.067,0:01:23.065 equal to the equilibrium[br]constant of water. 0:01:23.065,0:01:27.034 We learned that that's[br]10 to the minus 14. 0:01:27.034,0:01:32.051 Because water by itself will[br]have a hydrogen concentration 0:01:32.051,0:01:37.062 of 10 to the minus 7 and a[br]hydroxide concentration of 10 0:01:37.062,0:01:38.087 to the minus 7. 0:01:38.087,0:01:41.098 And if you take a log of[br]everything-- so if you take 0:01:41.098,0:01:46.028 the pKw-- 0:01:46.028,0:01:47.021 What was that? 0:01:47.021,0:01:49.018 If you put a p in front of[br]something, that means you're 0:01:49.018,0:01:51.001 taking the negative log of it. 0:01:51.001,0:01:54.046 So the negative log of 10 to the[br]minus 14-- the log base 10 0:01:54.046,0:01:57.004 up to the minus 14[br]is minus 14. 0:01:57.004,0:01:59.040 So the negative log[br]is just 14. 0:01:59.040,0:02:07.076 So pKw is 14 and that is equal[br]to-- if I take the negative 0:02:07.076,0:02:10.096 log of this side right here--[br]let me do that. 0:02:10.096,0:02:12.052 This is just a logarithm[br]property. 0:02:12.052,0:02:15.087 This is more math[br]than chemistry. 0:02:15.087,0:02:23.065 So the log of H plus times OH[br]times our hydroxide ion. 0:02:23.065,0:02:25.071 That's the same thing, just[br]the logarithm properties. 0:02:25.071,0:02:32.018 It's the same thing as minus[br]log of H plus minus, or you 0:02:32.018,0:02:40.015 could say plus the minus[br]log of OH minus. 0:02:40.015,0:02:41.072 And what is this? 0:02:41.072,0:02:48.053 well this is just the[br]pH, which is equal 0:02:48.053,0:02:49.090 to the minus log. 0:02:49.090,0:02:52.083 This is 10 to the[br]minus 7, right? 0:02:52.083,0:02:54.025 10 to the minus 7. 0:02:54.025,0:02:55.086 The log of that is minus 7. 0:02:55.086,0:02:56.065 You have the minus in front. 0:02:56.065,0:02:59.056 So its pH is equal to 7. 0:02:59.056,0:03:01.036 And what is this? 0:03:01.036,0:03:02.013 This over here. 0:03:02.013,0:03:05.090 This is our pOH. 0:03:05.090,0:03:08.071 The minus log of the hydroxide[br]concentration. 0:03:08.071,0:03:12.041 And of course, that was also[br]10 to the minus 7. 0:03:12.041,0:03:16.059 And so our pOH is equal to[br]log of that is minus 7. 0:03:16.059,0:03:17.058 You have a minus in front. 0:03:17.058,0:03:19.000 It's equal to 7. 0:03:19.000,0:03:24.005 So you get right there that[br]little formula that the pKw, 0:03:24.005,0:03:28.052 or the negative log of the[br]equilibrium constant of water, 0:03:28.052,0:03:41.024 pKw is equal to the pH of water[br]plus the pOH of water. 0:03:41.024,0:03:43.078 And this, at 25 degrees Celsius,[br]this is the thing 0:03:43.078,0:03:45.055 that's going to stay constant[br]because we're going to start 0:03:45.055,0:03:47.072 messing with these things[br]by throwing acid and 0:03:47.072,0:03:49.009 base into the water. 0:03:49.009,0:03:55.062 This thing is always going to[br]be 14 at 25 degrees Celsius. 0:03:55.062,0:03:57.081 Remember, as long as you keep[br]temperature constant and 0:03:57.081,0:04:01.022 you're not messing too much with[br]the molecule itself, your 0:04:01.022,0:04:03.019 equilibrium constant[br]stays constant. 0:04:03.019,0:04:04.093 That's why it's called[br]a constant. 0:04:04.093,0:04:08.071 So with all of that out of the[br]way, let's think about what 0:04:08.071,0:04:13.096 happens if I throw some acid[br]into a-- let's say I have some 0:04:13.096,0:04:15.021 hydrochloric acid. 0:04:15.021,0:04:18.099 0:04:18.099,0:04:21.025 I'll use colors more[br]creatively. 0:04:21.025,0:04:23.026 So I have some hydrochloric[br]acid. 0:04:23.026,0:04:26.069 It's in an aqueous solution. 0:04:26.069,0:04:32.089 We know that it disassociates[br]completely, which means that 0:04:32.089,0:04:39.039 we're just left with the[br]hydrogen ion, on which of 0:04:39.039,0:04:42.073 course really attaches itself to[br]another water molecule and 0:04:42.073,0:04:44.075 becomes hydronium. 0:04:44.075,0:04:51.056 Plus the chlorine anion,[br]or negative ion. 0:04:51.056,0:04:53.085 Right there. 0:04:53.085,0:05:09.007 And let's say that I do this[br]with 1 molar-- or, you know, 0:05:09.007,0:05:12.027 this is also sometimes written[br]as 1 capital M-- of 0:05:12.027,0:05:13.076 hydrochloric acid. 0:05:13.076,0:05:15.060 So essentially what[br]am I doing? 0:05:15.060,0:05:18.061 I am taking 1 molar of[br]hydrochloric acid, literally 0:05:18.061,0:05:26.098 means that I am taking 1[br]mole of HCl per liter 0:05:26.098,0:05:28.004 of our whole solution. 0:05:28.004,0:05:29.016 Which is mainly water. 0:05:29.016,0:05:30.075 It's an aqueous solution. 0:05:30.075,0:05:33.000 Per liter of water, right? 0:05:33.000,0:05:36.075 So what's my concentration going[br]to be of these things 0:05:36.075,0:05:37.037 right here? 0:05:37.037,0:05:39.012 Or in particular, what's[br]the concentration of 0:05:39.012,0:05:41.047 the H going to be? 0:05:41.047,0:05:46.025 Well, if this disassociated[br]completely, right? 0:05:46.025,0:05:49.033 So all of this stuff-- this is[br]not an equilibrium reaction. 0:05:49.033,0:05:49.093 Remember. 0:05:49.093,0:05:52.023 I only drew a one way[br]arrow to the right. 0:05:52.023,0:05:54.018 There's no even small[br]leftwards arrow. 0:05:54.018,0:05:57.025 This is a strong hydrochloric[br]acid. 0:05:57.025,0:06:01.050 So if you really put one molar[br]of this in an aqueous 0:06:01.050,0:06:03.038 solution, you're not going[br]to see any of this. 0:06:03.038,0:06:04.064 You're going to just see this. 0:06:04.064,0:06:11.029 So you're going to have the[br]hydrogen concentration here in 0:06:11.029,0:06:16.008 the aqueous solution is going[br]to be equal to 1 molar. 0:06:16.008,0:06:19.076 And there's also going to be 1[br]molar of chlorine anions, but 0:06:19.076,0:06:22.054 we don't care about that. 0:06:22.054,0:06:24.091 If I haven't said already, it[br]would be nice to figure out 0:06:24.091,0:06:27.032 what the pH of this[br]solution is. 0:06:27.032,0:06:29.082 Now that I've thrown[br]hydrochloric acid in it. 0:06:29.082,0:06:32.005 Well the pH is just the hydrogen[br]concentration. 0:06:32.005,0:06:36.093 0:06:36.093,0:06:38.063 We already have the hydrogen[br]concentration. 0:06:38.063,0:06:42.019 That's 1 molar, or 1 mole[br]per liter of solution. 0:06:42.019,0:06:53.044 So the pH is going to be equal[br]to the minus log base 10 of 0:06:53.044,0:06:54.076 our hydrogen concentration. 0:06:54.076,0:06:56.089 Of 1. 0:06:56.089,0:06:59.014 10 to the what power[br]is equal to 1? 0:06:59.014,0:07:01.097 Well, anything to the 0[br]of power is equal to 0:07:01.097,0:07:02.093 1, including 10. 0:07:02.093,0:07:05.098 So this is equal to 0[br]minus 0 is just 0. 0:07:05.098,0:07:07.038 So your pH is 0. 0:07:07.038,0:07:15.019 So if you have 1 molar of[br]hydrochloric acid, and you 0:07:15.019,0:07:19.005 throw it into an aqueous[br]solution. 0:07:19.005,0:07:21.094 And, well, I guess I'm saying[br]you're putting it into a 0:07:21.094,0:07:23.043 solution when I tell[br]you it's 1 molar. 0:07:23.043,0:07:26.075 So if you have a concentration[br]of 1 mole per liter of 0:07:26.075,0:07:31.019 solution, where the solvent[br]is water, you will end up 0:07:31.019,0:07:33.093 with a pH of 0. 0:07:33.093,0:07:35.018 The pH of 0. 0:07:35.018,0:07:38.004 0:07:38.004,0:07:43.075 So pH of water without[br]any acid in it, that 0:07:43.075,0:07:44.067 was equal to 7. 0:07:44.067,0:07:49.037 And this is considered[br]a neutral pH. 0:07:49.037,0:07:54.000 Now we know that if you were[br]to have an aqueous solution 0:07:54.000,0:07:59.001 with 1 molar of hydrochloric[br]acid, we can say-- I'll do it 0:07:59.001,0:08:07.092 in red because-- pH of HCl[br]in water is equal to 0. 0:08:07.092,0:08:11.043 So obviously a low pH[br]is more acidic. 0:08:11.043,0:08:14.061 And we went over that[br]in previous videos. 0:08:14.061,0:08:18.041 And let's figure out what the[br]pOH of hydrochloric acid is. 0:08:18.041,0:08:24.086 pOH of hydrochloric acid[br]in an aqueous solution. 0:08:24.086,0:08:28.049 Well, this all goes back to Le[br]Chatelier's Principle, right? 0:08:28.049,0:08:29.092 If you go back to what[br]we said before. 0:08:29.092,0:08:32.061 0:08:32.061,0:08:34.037 This is just pure water[br]right here. 0:08:34.037,0:08:37.054 If we may have put 1 molar of[br]hydrochloric acid in here, 0:08:37.054,0:08:46.007 we're essentially just throwing[br]a ton of hydrogen 0:08:46.007,0:08:46.095 protons in there. 0:08:46.095,0:08:50.026 We're substantially increasing[br]the concentration of this. 0:08:50.026,0:08:52.090 And Le Chatelier's Principle[br]says oh, well that means that 0:08:52.090,0:08:55.064 a lot of this is going to be[br]consumed and the reaction will 0:08:55.064,0:08:56.087 go and this direction. 0:08:56.087,0:08:59.015 The equilibrium reaction will[br]go in that direction. 0:08:59.015,0:09:00.012 But remember. 0:09:00.012,0:09:03.040 Water by itself only had a 10 to[br]the minus 7 concentration. 0:09:03.040,0:09:10.086 We're throwing in a million--[br]I mean it was one ten 0:09:10.086,0:09:13.022 millionth of a mole per liter. 0:09:13.022,0:09:17.011 Now we're throwing in--[br]what is that? 0:09:17.011,0:09:17.075 10 to the 7th. 0:09:17.075,0:09:22.035 We're throwing in 10 million[br]times as much hydrogen ions 0:09:22.035,0:09:23.048 into that water. 0:09:23.048,0:09:25.029 So all of this stuff[br]just gets consumed. 0:09:25.029,0:09:26.037 Maybe it goes there. 0:09:26.037,0:09:30.048 And so the concentration of this[br]gets thrown down really 0:09:30.048,0:09:32.061 far because we're[br]dumping so much. 0:09:32.061,0:09:34.095 And the concentration of this[br]goes up because it can only 0:09:34.095,0:09:37.001 consume so much of these guys. 0:09:37.001,0:09:38.042 There's not that much of this. 0:09:38.042,0:09:40.088 There's only 10 to the minus[br]7th molar of this. 0:09:40.088,0:09:43.017 So this ends up being 1 molar. 0:09:43.017,0:09:46.011 And if this ends up being 1[br]molar-- because 10 to the 0:09:46.011,0:09:48.041 minus 7th molar, essentially,[br]you can kind of view it as it 0:09:48.041,0:09:50.059 all gets consumed with[br]the stuff over here. 0:09:50.059,0:09:53.067 What ends up being the[br]concentration of the OH? 0:09:53.067,0:09:58.084 Well, we already know that the[br]pKw is 14 of water at 25 0:09:58.084,0:10:03.032 degrees, and the pKw of water[br]is equal to the pH of your 0:10:03.032,0:10:05.025 solution plus your pOH. 0:10:05.025,0:10:12.033 So if your pH for hydrochloric[br]acid is 0, right? 0:10:12.033,0:10:14.027 We have 1 molar of hydrochloric[br]acid. 0:10:14.027,0:10:19.059 Then your pOH of 1 molar of[br]hydrochloric acid is 14. 0:10:19.059,0:10:24.007 So right here, our pOH[br]is equal to 14. 0:10:24.007,0:10:26.015 Now let's do the same thing[br]with a base and figure out 0:10:26.015,0:10:26.097 what its pH is. 0:10:26.097,0:10:28.048 A strong base. 0:10:28.048,0:10:30.063 And I think you'll see that[br]it's the opposite. 0:10:30.063,0:10:35.070 So let's say I had potassium[br]hydroxide. 0:10:35.070,0:10:37.050 It's a strong base. 0:10:37.050,0:10:43.062 So it completely disassociates[br]in water to potassium cations. 0:10:43.062,0:10:46.022 Positively charged ions. 0:10:46.022,0:10:50.012 Plus hydroxide anions. 0:10:50.012,0:10:51.041 It completed disassociates. 0:10:51.041,0:10:53.064 So if I put anything in an[br]aqueous solution-- I should 0:10:53.064,0:10:54.089 write that down. 0:10:54.089,0:10:59.019 0:10:59.019,0:11:02.046 Aqueous solution just means we[br]are in water, of course. 0:11:02.046,0:11:05.094 And if we essentially put[br]1 molar-- remember the 0:11:05.094,0:11:07.008 concentration matters. 0:11:07.008,0:11:07.095 You can't just say,[br]oh, hydrochloric 0:11:07.095,0:11:09.032 acid has a pH of 0. 0:11:09.032,0:11:09.041 No. 0:11:09.041,0:11:11.032 You have to say 1 molar[br]of hydrochloric 0:11:11.032,0:11:13.070 acid has a pH of 0. 0:11:13.070,0:11:15.004 And actually I didn't[br]write that. 0:11:15.004,0:11:15.065 Let me write that. 0:11:15.065,0:11:16.090 1 molar. 0:11:16.090,0:11:19.028 0:11:19.028,0:11:22.037 And I'll leave you to figure out[br]what the pH or the pOH of 0:11:22.037,0:11:24.030 2 molars of hydrochloric[br]acid is. 0:11:24.030,0:11:26.095 Or a 10 molar of hydrochloric[br]acid. 0:11:26.095,0:11:29.070 And figure out what[br]those pH's are. 0:11:29.070,0:11:36.009 But if we have 1 molar, of[br]potassium hydroxide. 0:11:36.009,0:11:39.009 0:11:39.009,0:11:41.016 We have 1 molar of this. 0:11:41.016,0:11:42.094 And it completely disassociates 0:11:42.094,0:11:43.061 when it's in water. 0:11:43.061,0:11:47.061 So you have none of[br]this left over. 0:11:47.061,0:11:50.048 What's your concentration[br]of OH? 0:11:50.048,0:11:55.086 When your OH concentration[br]is going to be 1 molar. 0:11:55.086,0:11:56.007 Right? 0:11:56.007,0:11:58.029 If you had 1 mole per liter of[br]this, you're going to 1 mole 0:11:58.029,0:11:58.084 per liter of this. 0:11:58.084,0:12:01.016 Because all of this just[br]disappears in the water. 0:12:01.016,0:12:02.044 So what is your pOH? 0:12:02.044,0:12:05.035 0:12:05.035,0:12:08.025 POH is just the negative[br]log of this. 0:12:08.025,0:12:10.045 The log of 1 is 0. 0:12:10.045,0:12:12.070 The negative of 0 is 0. 0:12:12.070,0:12:19.012 And then your pH in this[br]circumstance-- well, you could 0:12:19.012,0:12:20.070 say, oh, it was the hydrogen[br]concentration. 0:12:20.070,0:12:22.054 You don't know what the hydrogen[br]concentration is, but 0:12:22.054,0:12:24.032 you know that when you throw[br]a bunch of this stuff, it's 0:12:24.032,0:12:26.016 going to sop up a bunch of[br]hydrogen and the hydrogen is 0:12:26.016,0:12:27.011 going to go down a lot. 0:12:27.011,0:12:28.048 But you're like, well,[br]how do I measure it? 0:12:28.048,0:12:29.064 Well, you remember it. 0:12:29.064,0:12:32.029 25 degrees Celsius. 0:12:32.029,0:12:34.092 The equilibrium constant[br]of water is equal to 0:12:34.092,0:12:37.013 the pH plus the pOH. 0:12:37.013,0:12:38.062 We showed that at the beginning[br]of the video. 0:12:38.062,0:12:43.025 So 14 is equal to[br]your pH plus 0. 0:12:43.025,0:12:45.042 That's our pOH in this case. 0:12:45.042,0:12:49.017 So our pH is 14. 0:12:49.017,0:12:52.072 So if you have 1 molar-- I used[br]potassium hydroxide in 0:12:52.072,0:12:55.082 this case-- but if you have 1[br]molar of a strong base-- let 0:12:55.082,0:12:57.030 me write that down. 0:12:57.030,0:13:05.044 1 molar of strong base. 0:13:05.044,0:13:08.021 Remember, strong is kind of an[br]official term in chemistry. 0:13:08.021,0:13:11.012 It means complete[br]disassociation. 0:13:11.012,0:13:17.098 You have a pH of 14 and[br]you have a pOH of 0. 0:13:17.098,0:13:22.044 If you have 1 molar[br]of strong acid. 0:13:22.044,0:13:25.067 If someone says that they have[br]something with a pH of 0 that 0:13:25.067,0:13:31.051 they would like to maybe throw[br]at you, you should decline. 0:13:31.051,0:13:34.063 Because it'll probably[br]hurt your 0:13:34.063,0:13:37.025 chances of-- well, anyway. 0:13:37.025,0:13:39.036 So let's say you have 1[br]molar of strong acid. 0:13:39.036,0:13:47.087 It's a pH of 0 and[br]a pOH of 14. 0:13:47.087,0:13:50.042 Anyway, maybe in the next video[br]I'll actually show you-- 0:13:50.042,0:13:52.058 This might give you the[br]impression that this is an 0:13:52.058,0:13:53.080 absolute scale. 0:13:53.080,0:13:57.049 That 0 is as acidic as you can[br]get, and 14 is as basic as you 0:13:57.049,0:13:59.028 can get when you get the[br]pH, but that's not 0:13:59.028,0:14:00.000 that's not the case. 0:14:00.000,0:14:01.062 You can actually get[br]above this or you 0:14:01.062,0:14:02.045 can get below this. 0:14:02.045,0:14:07.021 This was this when you had one[br]1 molar of a strong acid. 0:14:07.021,0:14:10.024 If you had 2 molars of a strong[br]acid-- actually if you 0:14:10.024,0:14:11.061 had 10 molars. 0:14:11.061,0:14:11.084 Right? 0:14:11.084,0:14:12.083 Let's say you get your hydrogen 0:14:12.083,0:14:19.090 concentration to 10 molar. 0:14:19.090,0:14:23.014 So if you had 10 molar of a[br]strong acid, you apply that in 0:14:23.014,0:14:24.008 an aqueous solution. 0:14:24.008,0:14:27.009 It is, when I say it's a[br]molar by definition. 0:14:27.009,0:14:28.075 What's your pH going to be? 0:14:28.075,0:14:33.001 Your pH is going to be the[br]minus log base 10 of 10. 0:14:33.001,0:14:34.041 The log, base 10 of 10, is 1. 0:14:34.041,0:14:36.026 10 to the first power is one. 0:14:36.026,0:14:37.083 So this is equal to minus 1. 0:14:37.083,0:14:40.076 So minus 1 pH would-- if[br]you had 10 molar of say 0:14:40.076,0:14:45.013 hydrochloric acid or nitric acid[br]or anything like that. 0:14:45.013,0:14:47.005 Anyway, that's all[br]for this video. 0:14:47.005,0:14:49.007 I'll see you in the next one.