1 00:00:00,000 --> 00:00:00,870 2 00:00:00,870 --> 00:00:03,240 Now that we know what a solution is, let's think a 3 00:00:03,240 --> 00:00:08,509 little bit about what it takes to get a molecule to be 4 00:00:08,509 --> 00:00:12,050 soluble into a solution or into a solvent. 5 00:00:12,050 --> 00:00:15,380 So let's say I start off with a salt, and I'll do a little 6 00:00:15,380 --> 00:00:17,839 side here, because in chemistry, you'll hear the 7 00:00:17,839 --> 00:00:20,079 word salt all the time. 8 00:00:20,079 --> 00:00:23,029 Let me right it down: salt. 9 00:00:23,030 --> 00:00:26,210 And in our everyday language, salt is table salt. 10 00:00:26,210 --> 00:00:29,830 It makes food salty, or sodium chloride. 11 00:00:29,829 --> 00:00:32,909 12 00:00:32,909 --> 00:00:37,500 And this indeed is both a salt from the Food Channel point of 13 00:00:37,500 --> 00:00:39,979 view and from the chemistry point of view, although the 14 00:00:39,979 --> 00:00:42,759 chemistry point of view does not care about what it does to 15 00:00:42,759 --> 00:00:44,030 season your food. 16 00:00:44,030 --> 00:00:46,325 The chemistry point of view, the reason why it's called a 17 00:00:46,325 --> 00:00:48,859 salt is because it's a neutral compound 18 00:00:48,859 --> 00:00:50,229 that's made with ions. 19 00:00:50,229 --> 00:00:55,419 So we all know that this is made when you take sodium. 20 00:00:55,420 --> 00:00:59,770 Sodium wants to lose its one electron in its valence shell. 21 00:00:59,770 --> 00:01:02,330 Chloride really wants to take it, so it does. 22 00:01:02,329 --> 00:01:08,009 Chloride becomes a negative ion and sodium is a positive 23 00:01:08,010 --> 00:01:12,109 ion, and they stick to each other really strongly because 24 00:01:12,109 --> 00:01:14,590 this guy's positive now, and this guy's negative after he 25 00:01:14,590 --> 00:01:16,930 took away his electron. 26 00:01:16,930 --> 00:01:19,140 Imagine your house is too small, so you have to give 27 00:01:19,140 --> 00:01:23,930 away your dog to someone who has room for the dog, but now 28 00:01:23,930 --> 00:01:26,200 you have to hang out at that person's house all the time 29 00:01:26,200 --> 00:01:28,570 because they have the dog you love. 30 00:01:28,569 --> 00:01:31,559 I don't know if that analogy was at all appropriate. 31 00:01:31,560 --> 00:01:32,379 But I think you get the idea. 32 00:01:32,379 --> 00:01:34,560 A salt is just any compound that's neutral. 33 00:01:34,560 --> 00:01:38,820 The other common ones, potassium chloride, you could 34 00:01:38,819 --> 00:01:46,439 do calcium bromide, or I could do a bunch of them, but these 35 00:01:46,439 --> 00:01:47,079 are all salts. 36 00:01:47,079 --> 00:01:49,429 And what we want to think about is what happens when you 37 00:01:49,430 --> 00:01:53,660 try to essentially dissolve these salts in water. 38 00:01:53,659 --> 00:01:57,799 So we know what water is doing, liquid water. 39 00:01:57,799 --> 00:02:00,170 So let me draw some liquid water. 40 00:02:00,170 --> 00:02:05,439 So if that's the oxygen and then you have two hydrogens 41 00:02:05,439 --> 00:02:09,301 that are kind of lumping off of it, I'll draw it like that. 42 00:02:09,301 --> 00:02:11,579 I'll draw a couple of them. 43 00:02:11,580 --> 00:02:17,760 And then, of course, you have another oxygen here. 44 00:02:17,759 --> 00:02:21,370 Maybe the hydrogens are in this orientation because the 45 00:02:21,370 --> 00:02:24,909 hydrogen ends are attracted through hydrogen bonds-- we've 46 00:02:24,909 --> 00:02:27,699 learned this-- to the oxygen ends because this has a slight 47 00:02:27,699 --> 00:02:30,560 negative charge here, a slight positive charge here. 48 00:02:30,560 --> 00:02:32,199 These are the hydrogen bonds that we've 49 00:02:32,199 --> 00:02:33,719 talked so much about. 50 00:02:33,719 --> 00:02:40,270 And maybe you have another oxygen here and it's got its 51 00:02:40,270 --> 00:02:44,710 hydrogens there and there. 52 00:02:44,710 --> 00:02:46,740 You have some hydrogen bonds there. 53 00:02:46,740 --> 00:02:49,310 I could do another oxygen here, and you can kind of see 54 00:02:49,310 --> 00:02:52,069 the structure that forms, although what I'm drawing, 55 00:02:52,069 --> 00:02:55,699 this is actually more of a-- if you were in a solid state, 56 00:02:55,699 --> 00:02:57,009 this would be kind of rigid and they would 57 00:02:57,009 --> 00:02:57,859 just vibrate in place. 58 00:02:57,860 --> 00:03:00,260 In the liquid state, they're all moving around. 59 00:03:00,259 --> 00:03:03,590 They're rubbing up against each other, but they're 60 00:03:03,590 --> 00:03:05,670 staying very close. 61 00:03:05,669 --> 00:03:08,339 Actually, the liquid state for water is actually the most 62 00:03:08,340 --> 00:03:09,950 compact state for water. 63 00:03:09,949 --> 00:03:12,859 Now, when you're dealing with stuff like this-- these are 64 00:03:12,860 --> 00:03:15,380 moving around, maybe this guy's moving that way, that 65 00:03:15,379 --> 00:03:18,620 guy's moving that way-- and you want to dissolve something 66 00:03:18,620 --> 00:03:19,469 like sodium chloride. 67 00:03:19,469 --> 00:03:21,620 Sodium chloride's actually quite a large molecule. 68 00:03:21,620 --> 00:03:24,740 If you look at the Periodic Table up here, oxygen is a 69 00:03:24,740 --> 00:03:27,310 Period 2 element. 70 00:03:27,310 --> 00:03:28,740 Hydrogen is very small. 71 00:03:28,740 --> 00:03:30,730 We know when it gets into a hydrogen bond with oxygen, 72 00:03:30,729 --> 00:03:33,609 it's really just a proton sitting out there because all 73 00:03:33,610 --> 00:03:36,060 the electrons like to hang out with the oxygen, while, say, 74 00:03:36,060 --> 00:03:39,390 sodium and chloride, they're considerably larger. 75 00:03:39,389 --> 00:03:42,239 I won't go into the exact molecular sizes, but maybe 76 00:03:42,240 --> 00:03:46,439 sodium-- let's do sodium-- which actually, just as a 77 00:03:46,439 --> 00:03:47,919 review, which is larger. 78 00:03:47,919 --> 00:03:50,149 We know that it becomes smaller as you go to the right 79 00:03:50,150 --> 00:03:54,450 of the Periodic Table, so sodium is quite a large atom, 80 00:03:54,449 --> 00:03:57,229 while chloride is a good bit smaller, but they're both 81 00:03:57,229 --> 00:04:00,030 bigger than oxygen and a lot bigger than hydrogen. 82 00:04:00,030 --> 00:04:02,000 So let me draw that. 83 00:04:02,000 --> 00:04:06,169 So sodium-- I'll do sodium as a positive. 84 00:04:06,169 --> 00:04:07,829 It's pretty big. 85 00:04:07,830 --> 00:04:09,080 Maybe it looks like this. 86 00:04:09,080 --> 00:04:12,800 87 00:04:12,800 --> 00:04:16,110 Sodium is positive and then you have the chloride. 88 00:04:16,110 --> 00:04:18,959 The chloride I'll do in purple. 89 00:04:18,959 --> 00:04:20,862 They're still pretty big. 90 00:04:20,862 --> 00:04:25,050 The chloride, it'll look like this. 91 00:04:25,050 --> 00:04:27,460 And what happens when you put it into water, it 92 00:04:27,459 --> 00:04:28,329 disassociates. 93 00:04:28,329 --> 00:04:30,779 Even though these guys in a solid state, they're 94 00:04:30,779 --> 00:04:32,439 jam-packed to each other. 95 00:04:32,439 --> 00:04:36,930 When you put it into water, the positive cations are 96 00:04:36,930 --> 00:04:40,350 attracted to the negative partial charges on the oxygen 97 00:04:40,350 --> 00:04:44,110 side of the water, and the negative anions are attracted 98 00:04:44,110 --> 00:04:45,735 to the positive sides of the hydrogen. 99 00:04:45,735 --> 00:04:48,569 100 00:04:48,569 --> 00:04:54,399 But in order to get, for example, this sodium ion into 101 00:04:54,399 --> 00:04:57,120 the water, it has to fit in there. 102 00:04:57,120 --> 00:04:59,560 So, for example, I drew this as a liquid initially, but if 103 00:04:59,560 --> 00:05:01,860 this was a solid and you had this structure, it would be 104 00:05:01,860 --> 00:05:03,000 extremely difficult. 105 00:05:03,000 --> 00:05:05,769 In fact, it would be next to impossible to squeeze these 106 00:05:05,769 --> 00:05:09,449 huge sodium ions in place to make it soluble 107 00:05:09,449 --> 00:05:11,139 into, say, solid ice. 108 00:05:11,139 --> 00:05:14,539 And as even cold water, these bonds are still going to be 109 00:05:14,540 --> 00:05:16,560 pretty strong and they're going to be just kind of 110 00:05:16,560 --> 00:05:18,589 barely moving past each other because there's not a lot of 111 00:05:18,589 --> 00:05:19,284 kinetic energy. 112 00:05:19,285 --> 00:05:23,710 So what you need to do is, the warmer the water you have-- I 113 00:05:23,709 --> 00:05:25,949 mean, you can fit it into cold water, because at least cold 114 00:05:25,949 --> 00:05:30,339 water has some give, but the warmer the better, because you 115 00:05:30,339 --> 00:05:34,589 have some kinetic energy, and that essentially gives space. 116 00:05:34,589 --> 00:05:38,084 Or it makes room for this sodium ion that's entering in 117 00:05:38,084 --> 00:05:40,959 to kind of bump its way into a configuration that's 118 00:05:40,959 --> 00:05:41,870 reasonably stable. 119 00:05:41,870 --> 00:05:43,829 And a reasonably stable configuration would look 120 00:05:43,829 --> 00:05:46,459 something like this. 121 00:05:46,459 --> 00:05:50,579 Sodium would look-- and then you'd have a bunch of-- sodium 122 00:05:50,579 --> 00:05:51,599 is positive. 123 00:05:51,600 --> 00:05:53,860 It would be attracted to the negative end of the water 124 00:05:53,860 --> 00:05:58,280 molecules, so the oxygen end. 125 00:05:58,279 --> 00:06:00,949 So it looks like that, the oxygen end, and then the 126 00:06:00,949 --> 00:06:02,199 hydrogen ends are going to be pointing 127 00:06:02,199 --> 00:06:03,449 in the other direction. 128 00:06:03,449 --> 00:06:06,444 129 00:06:06,444 --> 00:06:11,310 The hydrogen ends are going to be on the other side. 130 00:06:11,310 --> 00:06:14,370 And, of course, the chlorine atom is going to be very 131 00:06:14,370 --> 00:06:17,740 attracted to that other side, so the chlorine atom might be 132 00:06:17,740 --> 00:06:19,829 right over here. 133 00:06:19,829 --> 00:06:22,359 134 00:06:22,360 --> 00:06:24,569 So the chlorine atom might want to hang out right here. 135 00:06:24,569 --> 00:06:27,870 136 00:06:27,870 --> 00:06:31,139 In order to get as much of the sodium chloride into your 137 00:06:31,139 --> 00:06:32,839 water sample, you want to heat up the 138 00:06:32,839 --> 00:06:34,219 water as much as possible. 139 00:06:34,220 --> 00:06:38,380 Because what that does is it allows these bonds to not be 140 00:06:38,379 --> 00:06:42,159 taken as seriously and these relatively huge atoms to kind 141 00:06:42,160 --> 00:06:43,740 of bump their way in. 142 00:06:43,740 --> 00:06:53,230 So, in general, if you think about solubility of a solute 143 00:06:53,230 --> 00:06:58,080 in water-- or especially if you think of a solid solute, 144 00:06:58,079 --> 00:07:03,740 which is sodium chloride-- into a liquid solvent, then 145 00:07:03,740 --> 00:07:05,860 the higher the temperature while you're in the liquid 146 00:07:05,860 --> 00:07:09,490 state, the more of the solid you're going to be able to get 147 00:07:09,490 --> 00:07:11,480 into the liquid, or you're going to raise solubility. 148 00:07:11,480 --> 00:07:17,110 So temperature goes up, solubility goes up. 149 00:07:17,110 --> 00:07:19,470 For example, if you were to take some table salt, and you 150 00:07:19,470 --> 00:07:20,450 could experiment with this. 151 00:07:20,449 --> 00:07:24,235 It doesn't seem too dangerous and not too expensive because 152 00:07:24,235 --> 00:07:25,650 salt is reasonably cheap. 153 00:07:25,649 --> 00:07:27,489 Keep putting it into a glass, and at 154 00:07:27,490 --> 00:07:29,280 some point it'll dissolve. 155 00:07:29,279 --> 00:07:31,049 You could shake it a little bit, just to make sure. 156 00:07:31,050 --> 00:07:33,030 You could think about what's happening at the molecular 157 00:07:33,029 --> 00:07:35,279 level while you shake it and why does that help to shake or 158 00:07:35,279 --> 00:07:36,299 stir things? 159 00:07:36,300 --> 00:07:41,389 But at some point, you're going to end up with-- if this 160 00:07:41,389 --> 00:07:46,079 is your glass of water, the salt will keep going in there, 161 00:07:46,079 --> 00:07:49,310 but at some point, you'll have salt crystals at the bottom of 162 00:07:49,310 --> 00:07:50,160 your glass. 163 00:07:50,160 --> 00:07:54,290 At that point, your water is saturated with salt at the 164 00:07:54,290 --> 00:07:56,540 temperature that you're trying to deal with it. 165 00:07:56,540 --> 00:07:58,680 Now, right when you start seeing that, if you were to 166 00:07:58,680 --> 00:08:00,949 put it in the microwave or if you were to heat it up, you 167 00:08:00,949 --> 00:08:04,639 would see that even these guys are able to be absorbed in the 168 00:08:04,639 --> 00:08:07,289 water, and that's because the extra kinetic energy from the 169 00:08:07,290 --> 00:08:09,910 temperature is making it more likely that these guys are 170 00:08:09,910 --> 00:08:12,800 going to be able to bump out of configuration for just long 171 00:08:12,800 --> 00:08:15,259 enough for these guys to bump in. 172 00:08:15,259 --> 00:08:19,879 And just a little side note, when you take these salts, 173 00:08:19,879 --> 00:08:22,969 which are just ionic compounds that are neutral, they're made 174 00:08:22,970 --> 00:08:25,200 of ions, but they cancel each other out. 175 00:08:25,199 --> 00:08:28,649 When you put them in water, these compounds by themselves 176 00:08:28,649 --> 00:08:30,709 aren't normally-- when they're in the solid state, they don't 177 00:08:30,709 --> 00:08:32,079 normally conduct electricity. 178 00:08:32,080 --> 00:08:34,158 Even though they're charged, they're very closely stuck to 179 00:08:34,158 --> 00:08:35,960 each other, so there's not a lot of room 180 00:08:35,960 --> 00:08:37,600 for movement of charge. 181 00:08:37,600 --> 00:08:40,450 But once you disassociate them in water or dissolve them in 182 00:08:40,450 --> 00:08:42,610 water, now, all of a sudden, you have these floating 183 00:08:42,610 --> 00:08:48,039 charges in the water, and this does conduct electricity, so 184 00:08:48,039 --> 00:08:53,339 it becomes quite a reasonable conductor of electricity. 185 00:08:53,340 --> 00:08:55,710 So the general rule of thumb is, if you're dealing with a 186 00:08:55,710 --> 00:08:58,670 solid in a liquid solvent, lowering the temperature will 187 00:08:58,669 --> 00:09:01,339 decrease the solubility, because it's harder to jam the 188 00:09:01,340 --> 00:09:03,690 molecules in there, and increasing the temperature 189 00:09:03,690 --> 00:09:05,050 will increase the solubility. 190 00:09:05,049 --> 00:09:05,959 But what about a gas? 191 00:09:05,960 --> 00:09:12,090 What if you make some soda and you want to dissolve some 192 00:09:12,090 --> 00:09:16,269 carbon dioxide into, let's say, water again? 193 00:09:16,269 --> 00:09:19,110 So here, the way to think about it when we did it with 194 00:09:19,110 --> 00:09:21,759 salts, these are ionic compounds. 195 00:09:21,759 --> 00:09:24,669 They had some natural attraction to the different 196 00:09:24,669 --> 00:09:27,209 polar ends of the water molecule. 197 00:09:27,210 --> 00:09:30,210 But gases, for the most part, do not have 198 00:09:30,210 --> 00:09:32,420 strong attractive forces. 199 00:09:32,419 --> 00:09:34,250 That's why they're gases, especially at room 200 00:09:34,250 --> 00:09:34,659 temperature. 201 00:09:34,659 --> 00:09:37,679 They like to be free. 202 00:09:37,679 --> 00:09:40,699 A gas, they have a good bit of kinetic energy, but more 203 00:09:40,700 --> 00:09:46,610 important, the bonds between them, for example, in ideal 204 00:09:46,610 --> 00:09:48,899 gases we talked about it, they just have their London 205 00:09:48,899 --> 00:09:49,809 dispersion forces. 206 00:09:49,809 --> 00:09:52,639 They have very weak bonds, and that's why at, say, the same 207 00:09:52,639 --> 00:09:55,590 temperature and pressure that water would be a liquid, a lot 208 00:09:55,590 --> 00:09:57,180 of these gases are gases. 209 00:09:57,179 --> 00:09:59,189 They jump away from each other because they don't want to 210 00:09:59,190 --> 00:10:00,520 touch each other. 211 00:10:00,519 --> 00:10:02,949 Now, when you put this in liquid, and this is at least 212 00:10:02,950 --> 00:10:05,160 my intuition, so let's just say this is a bunch of water 213 00:10:05,159 --> 00:10:08,600 molecules here. 214 00:10:08,600 --> 00:10:13,550 If you were to dissolve-- let's say it's carbon dioxide. 215 00:10:13,549 --> 00:10:15,459 You can ignore this stuff up here. 216 00:10:15,460 --> 00:10:20,210 If you were to dissolve carbon dioxide in water-- so if you 217 00:10:20,210 --> 00:10:23,300 were to dissolve this in water, so those are some 218 00:10:23,299 --> 00:10:24,699 carbon dioxide molecules. 219 00:10:24,700 --> 00:10:28,259 I'm just drawing the whole molecule as a circle. 220 00:10:28,259 --> 00:10:31,879 What do these molecules want to do? 221 00:10:31,879 --> 00:10:34,529 It's natural state is a gas and it is a gas at let's say 222 00:10:34,529 --> 00:10:39,000 the standard pressure, so it really wants to escape from 223 00:10:39,000 --> 00:10:42,309 this water, but it just can't do it that easily because 224 00:10:42,309 --> 00:10:45,129 there's water molecules all around it, right? 225 00:10:45,129 --> 00:10:47,379 This guy right here, he might want to bump out, but he's 226 00:10:47,379 --> 00:10:48,629 surrounded by water molecules. 227 00:10:48,629 --> 00:10:51,570 228 00:10:51,570 --> 00:10:53,590 So what would help him bump out? 229 00:10:53,590 --> 00:10:57,139 Well, if you raise the average kinetic energy of the system, 230 00:10:57,139 --> 00:10:59,159 if you made all of these guys, that these guys were moving 231 00:10:59,159 --> 00:11:01,719 faster, and especially if the carbon dioxide molecules 232 00:11:01,720 --> 00:11:04,180 themselves had more kinetic energy, then maybe 233 00:11:04,179 --> 00:11:05,259 they could break out. 234 00:11:05,259 --> 00:11:08,389 And as you have from personal experience with Coke bottles, 235 00:11:08,389 --> 00:11:10,470 you could also shake the system, because if you shake 236 00:11:10,470 --> 00:11:13,940 the system, it just moves everything around enough that 237 00:11:13,940 --> 00:11:15,500 these guys can escape. 238 00:11:15,500 --> 00:11:18,860 So when you're dissolving a gas inside of a liquid 239 00:11:18,860 --> 00:11:22,139 solvent, when the solute is a gas, it actually has the 240 00:11:22,139 --> 00:11:25,419 opposite effect, that rising temperature. 241 00:11:25,419 --> 00:11:31,500 So when temperature goes up, solubility goes down because 242 00:11:31,500 --> 00:11:33,009 these guys want to escape. 243 00:11:33,009 --> 00:11:33,980 They want to be free. 244 00:11:33,980 --> 00:11:36,220 They want to be away from other molecules and they want 245 00:11:36,220 --> 00:11:39,500 to bounce around in open-- I shouldn't use the word air-- 246 00:11:39,500 --> 00:11:41,100 in open space. 247 00:11:41,100 --> 00:11:43,940 And so anything that lets the system move around more, 248 00:11:43,940 --> 00:11:44,550 they're going to go up. 249 00:11:44,549 --> 00:11:49,569 And likewise, if temperature goes down, solubility goes up. 250 00:11:49,570 --> 00:11:51,890 The other factor, and it's not as big of a factor when you 251 00:11:51,889 --> 00:11:56,519 talk about a solid solute, but when you talk about a liquid 252 00:11:56,519 --> 00:11:57,720 solute-- let me just do it again. 253 00:11:57,720 --> 00:12:00,879 So those are the carbon dioxide molecules and then you 254 00:12:00,879 --> 00:12:04,730 have a bunch of water molecules-- they should all be 255 00:12:04,730 --> 00:12:07,629 the same size-- that it's dissolved in. 256 00:12:07,629 --> 00:12:09,730 I think you get the idea. 257 00:12:09,730 --> 00:12:12,340 Pressure is also a big factor. 258 00:12:12,340 --> 00:12:14,800 I already said that these guys, their natural state is 259 00:12:14,799 --> 00:12:15,479 to roam free. 260 00:12:15,480 --> 00:12:17,320 They want to get out. 261 00:12:17,320 --> 00:12:19,660 They want to somehow bounce out of the water. 262 00:12:19,659 --> 00:12:23,049 But if you have a really high pressure up here-- just the 263 00:12:23,049 --> 00:12:26,269 atmosphere up here has just tons of molecules bouncing 264 00:12:26,269 --> 00:12:30,590 really hard down on the surface of our solution-- so 265 00:12:30,590 --> 00:12:35,240 if there's just tons of molecules bouncing really hard 266 00:12:35,240 --> 00:12:37,180 off the surface, it'll be harder for 267 00:12:37,179 --> 00:12:39,359 anything to escape upwards. 268 00:12:39,360 --> 00:12:41,950 And that's why, when you have pressure going up, or at least 269 00:12:41,950 --> 00:12:45,759 this is the intuition, when pressure goes up, solubility 270 00:12:45,759 --> 00:12:49,620 of a gas also goes up. 271 00:12:49,620 --> 00:12:51,120 And this is for a gas. 272 00:12:51,120 --> 00:12:54,039 So just the interesting thing to remember is that when you 273 00:12:54,039 --> 00:12:57,539 think about solubility, solids do the inverse of gas. 274 00:12:57,539 --> 00:13:01,000 Temperature is good for solid solubility, right? 275 00:13:01,000 --> 00:13:03,860 We said when you put salt or sugar in water, it's good to 276 00:13:03,860 --> 00:13:04,750 increase the temperature. 277 00:13:04,750 --> 00:13:06,570 You'll be able put more in there. 278 00:13:06,570 --> 00:13:09,340 On the other hand, with a gas, it's the opposite. 279 00:13:09,340 --> 00:13:13,160 You want colder temperatures to put more gas into the 280 00:13:13,159 --> 00:13:16,709 solution, or you want higher pressure to keep it-- at least 281 00:13:16,710 --> 00:13:19,930 in the way my mind works-- from escaping out the top. 282 00:13:19,929 --> 00:13:22,239 Anyway, hope you found that useful.