1 Gavin Interview_02.28.2013 2 3 [00:01:07.18] 4 5 G: I also - - PDF document

Gavin Interview_02.28.2013 1 2 [00:01:07.18] 3 4 G: I also remember there were a lot of issues between Prof. Redish and Prof. Losert 5 that they talked about, about who was in agreement with what... that people in the 6 class who had a lot more background in biology than we felt than our professors do, 7 because you know, they're physicists. And basically just what we've learned 8 immediately over the course of the last 2 to 3 years... we felt that what we had been 9 taught versus what they were arguing was in violation of each other... 10 11 [00:01:39.16] 12 13 [00:03:28.29] 14 15 I: Alright so let's go through it one at a time. So you said you answered A which was 16 'a nonpolar hydrocarbon is more attracted to another hydrocarbon than to water... 17 so why do you... what were you thinking that made that correct... or one of the 18 reasons for why oil and water separate? 19 20 G: It's just basic BSci 105 and Chem 131... I feel like it was just something that we've 21 been told since the beginning of our college careers, maybe even beforehand if other 22 people had taken AP, stuff like that. We were always told that opposites in 23 electricity attract and likes attract when you're talking about polarities. You know, 24 polar likes polar, and nonpolar likes nonpolar, um, and if nonpolar is with polar they 25 are not going to agree with each other and that's why you have proteins that are 26 going to have the nonpolar ends on the inside when they're in water and the polar 27 ends on the outside because otherwise it's just it's gonna (?) and it's not gonna like 28 it. 29 30 [00:04:33.23] 31 32 I: So if I have a water molecule... say a bunch of water molecules here (drawing a 33 vertical line of water molecules on the board) and then over here I have just a 34 hydrocarbon (draws a hydrocarbon chain vertically next to the line of water 35 molecules), so I have a nonpolar thing and a polar thing... and then I bring in a 36 different hydrocarbon (draws a hydrocarbon chain above the two lines already 37 drawn, midway between them)... are you saying that it (the top hydrocarbon) will be 38 atrracted to one of these (the lower hydrocarbon and the water chain) more than 39 the other? 40 41 G: I would think so. 42 43 I: OK, which one? 44 45

G: I would say that that hydrocarbon (upper) would be more attracted to that 46 hydrocarbon (lower) and the thing is too is that I don't think anyone in my class 47 actually knows why that is specifically. I think we just know that we've always been 48 told they go together. So we skip the whole intermediate 'how it happens' and jump 49 to the conclusion, well, that (upper hydrocarbon) has to go to that (lower 50 hydrocarbon). But my overall understanding of why that is is pretty weak. 51 52 [00:05:40.12] 53 54 I would assume that because all that's sticking out here (hydrocarbon) is hydrogens 55 and the charge is equally dispersed throughout the molecule, whereas here (line of 56 water molecules) you have higher electron density here (oxygen end) than you 57 would over here (hydrogen end) so you create positive on this (hydrogen) end, so 58 sort of my assumption when you would say these two (hydrocarbon and water) 59 interact with each other, you'd have the oxygens forming weak but still existent 60 hydrogen bonds with the hydrogens that are sticking out from the carbons (on the 61 hydrocarbon chain). 62 63 I: These oxygens and these you mean? (pointing between the water oxygen and the 64 hydrocarbon hydrogen) 65 66 G: Yes. And then because of the electronegativity that they (oxygens) have, because 67 they have these extra electrons that are capable of forming those weak bonds, those 68 weak interactions. That was sort of my assumption and I haven't even been 69 confirmed on that. 70 71 I: Wait, so you're talking about why this (water) would be attracted to that 72 (hydrocarbon), right? 73 74 G: Right. And that's when I was saying when they were mixed together in water, 75 but then you have these (the two hydrocarbons) more next to each other, you'd 76 have these associated with each other more readily than you would this 77 (hydrocarbon and water) when this (upper hydrocarbon) is introduced but why 78 that is I'm not sure. 79 80 I: Ok. 81 [00:06:49.15] 82 83 [Brief discussion about van der Waals forces. Gavin says he expects polar‐polar 84 interaction to be strongest and nonpolar‐polar is weakest because they are not 85 alike...) 86 87 [00:08:27.08] 88 89 I: So let me ask it I guess this way... what makes any two of these things (points to 90 board) interact at all? 91

92 G: Um, it's gonna have to be you know the attraction forces of the electrons and the 93 nuclei with one another. I remember when we had you know the blackboard and 94 balloon example when you charge the balloon you know you're going to have a lot of 95 charge on it and then you're gonna have a very inert blackboard, but whenever you 96 move the balloon towards the blackboard, the electrons in the blackboard are going 97 to push away a little bit because the negative charge on the ballon is gonna force it 98 backwards becaude it's a such a solid structure that the protons themselves are not 99 going to move but electrons are more capable of moving. 100 101 I: Right ok. So in that explanation, like you're describing interactions between 102 electrons and protons which sounds like what you were saying about how opposite 103 charges attract right? 104 105 [00:09:41.19] 106 107 G: Right so we can have you know these hydrogens coming off (of the hydrocarbon 108 chain) and they're going to have a balance of charge with the carbon that's right 109 there, but then this (draws electron pairs on the oxygens on the water molecules) 110 and so even though you have a relatively stable structure you have all these 111 electrons that even though they don't really want to they are capable... so you have 112 all these weak interactions (draws dotted lines between the water oxygens and the 113 hydrocarbon hydrogens) that would form if they were close enough... [goes on to 114 explain hydrogen bonding in more detail] 115 116 I: Ok, so if you drew the same thing but can you draw 2 hydrocarbons? How would 117 that interaction look like? 118 119 G: (draws the second hydrocarbon next to the first and explain the structures)... so 120 you have a carbon which has 4 electrons and as you can tell this carbon here and 121 this carbon here are taking two of them they are sharing them, and then these two 122 hydrogens are also sharing the other two, so this generally has a charge of zero. but 123 because these hydrogens... that's where it's difficult because you say why are these 124 gonna want to interact with each other more than these (waters)... and I see what 125 you're getting at. 126 127 [00:11:26.17] 128 129 And we haven't talked about that. In physics especially. We didn't talk about these 130 individual interactions so much as the big picture, and in my chemistry classes and 131 in my biology classes at least to my understanding I don't remember us discussing 132 that, just that these (two hydrocarbons) want to be together and these (waters) 133 want to be together. But not this (points to dotted line bond between the water and 134 hydrocarbon that he had drawn earlier) even though at the same time I can actually 135 see this interaction (water‐hydrocarbon) being stronger than this one 136

(hydrocarbon‐hydrocarbon)... even though this one (hydrocarbon‐hydrocarbon) is 137 more favorable than this one (water‐hydrocarbon). 138 139 I: Gotcha.... so does that bother you? 140 141 G: Yes. Now it does :) 142 143 144 147 148 Elena Interview_02.27.2013 149 150 151 [00:13:19.25] 152 153 I: So let me ask it this way. If you were now going to say to a friend why oil and 154 water don't mix, how would you explain it? 155 156 E: Ok. I would say because oil wants to be together with other oil molecules and not 157 be mixing with other polar molecules because oil is nonpolar. And, I don't... I don't 158 really... I mean that's basically what I would say. 159 160 I: Right. 161 162 E: Because noww... cause yeah and I would say that even though the oxygen from 163 the water and the hydrogen from the hydrocarbon would have a stronger 164 interaction, the hydrocarbon chains are really long, and those would all together add 165 up to make a stronger interaction, I guess. 166 167 I: And, so from what you just said, do you feel like it's necessary to talk about 168 entropy at all? Cause you just gave an explanation... 169 170 E: Yeah, I know. It would depend on who I was explaining it to, because I now just 171 understand it more than I ever have and I've talked about it in so many other 172 classes... if I'm trying to explain it to one of my other classmates I would talk about 173

• entropy. But if I was trying to explain it to someone else I wouldn't (laughs).

174 175 I: So if you were talking to a classmate, what would you say? 176 177 E: I would say that when oil is separate from water it's in its own layer, it can 178 interact more with other oil molecules and be in more different places, and that's 179 more microstates, and an increase in microstates you have more disorder and 180 more... or higher entropy. 181 182

I: Yeah. You said when I asked you just now that the longer hydrocarbon than the 183 water molecules means that maybe the interaction between two hydrocarbons is 184 larger than the interaction between A hydrocarbon and A water molecule... but what 185 about if you had a line of water molecules? 186 187 E: Yeah (smiles having anticipated the question)... I don't know, I would have to 188 look at the numbers. 189 190 I: Sure, ok. Yeah, I agree. And if the numbers came out that the water line was more 191 attracted to the hydrocarbon line than two hydrocarbon lines were, would that 192 bother you? 193 194 E: That would bother me. 195 196 I: Why would that bother you? 197 198 [00:15:56.01] 199 200 E: Because then to me it would just seem like, well, why wouldn't water completely 201 surround each individual hydrocarbon, if it overall has the stronger interaction than 202 the hydrocarbon with the hydrocarbon? 203 204 I: So in terms of this (points to deltaG = deltaH ‐ TdeltaS equation on whiteboard), 205 what would the story be if the line of water is attracted more to the line of 206 hydrocarbons (than are two hydrocarbon lines)? 207 208 E: Ok, so, now this is where I kind of have two separate thoughts. Here (sort of 209 points toward the page) we are talking about like electrostatic interactions... 210 211 I: Where do those go (looking toward the board)? 212 213 E: I just don't feel like they're involved in there (circuling the equation with her 214 hand) at all! So that's why I'm kind of having trouble like piecing the two together in 215 my mind. 216 217 I: OK, gotcha. 218 219 E: And I think that's also why that (quiz) question really confused me when Prof. 220 Losert and Redish brought up electrostatic interactions. Like I'm thinking entropy 221 (points toward G = H ‐ TS equation on whiteboard) and you're thinking electrostatic 222

• interactions. How do those come together?

223 224 [00:16:54.26] 225 226

I: Um, in the recitation, when you were talking about the energy vs the entropy, or 227 the enthalpy vs the entropy, what was determining the deltaH? What was the 228 energy? 229 230 E: We said it was zero. 231 232 I: For the oil and water? 233 234 E: Yeah, or maybe we said... 235 236 I: OK, how did you determine whether it was zero or anything else? 237 238 E: Ok (she draws on the board), so deltaH = deltaU + pdeltaV. So we were saying 239 that the internal energy doesn't change, I think that's what we said because in the 240 beginning it says that thermodynamic equilibrium or something like that... 241 242 (at this point I become pretty sure she's thinking of a different recitation, about free 243 expansion) 244 245 I: I think we might be getting... I think you might be thinking of this one? (show her 246 the free expansion recitation). 247 248 E: OH!! Yes! That's.. 249 250 I: This one was, right, you said it was thermally isolated... the temperature wasn't 251 changing. 252 253 E: There are just too many problems in this class... Actually I think we did say that 254 deltaH was nonzero. 255 256 I: OK, but like what factors helped you to think about whether it was positive or 257 negative, like what were you thinking about to determine deltaH for the process of 258

• il and water?

259 260 E: Internal energy. 261 262 I: And what did that, how did you figure out what sign that had? 263 264 E: We were thinking, well is the internal energy changing? (thinks about it...) I 265 honestly don't remember what we said... I feel like it was... positve? Well, ok, so if 266 you have interactions, you have bonds and you're breaking bonds and reforming 267 them... I think that's where we got it from. 268 269 I: ok. 270 271

E: So actually I guess the interactions, they're electrostatic interactions, so now it 272 makes sense. (Laughs). 273 274 [00:19:01.23] 275 276 I: Ok, so I could see how the electrostatic stuff where you're thinking about charges 277 exerting forces doesn't feel the same as bonds necessarily? 278 279 E: Yeah... 280 281 I: But you were thinking about bonds probably when you were thinking about 282 deltaU... 283 284 E: We were thinking about it.... that (points to board) will help be for my exam on 285 Friday (laughs). 286