1 Gavin Interview_02.28.2013 2 3 [00:01:07.18] 4 5 G: I also remember there were a lot of issues between Prof. Redish and Prof. Losert 6 that they talked about, about who was in agreement with what... that people in the 7 class who had a lot more background in biology than we felt than our professors do, 8 because you know, they're physicists. And basically just what we've learned 9 immediately over the course of the last 2 to 3 years... we felt that what we had been 10 taught versus what they were arguing was in violation of each other... 11 12 [00:01:39.16] 13 14 [00:03:28.29] 15 16 I: Alright so let's go through it one at a time. So you said you answered A which was 17 'a nonpolar hydrocarbon is more attracted to another hydrocarbon than to water... 18 so why do you... what were you thinking that made that correct... or one of the 19 reasons for why oil and water separate? 20 21 G: It's just basic BSci 105 and Chem 131... I feel like it was just something that we've 22 been told since the beginning of our college careers, maybe even beforehand if other 23 people had taken AP, stuff like that. We were always told that opposites in 24 electricity attract and likes attract when you're talking about polarities. You know, 25 polar likes polar, and nonpolar likes nonpolar, um, and if nonpolar is with polar they 26 are not going to agree with each other and that's why you have proteins that are 27 going to have the nonpolar ends on the inside when they're in water and the polar 28 ends on the outside because otherwise it's just it's gonna (?) and it's not gonna like 29 it. 30 31 [00:04:33.23] 32 33 I: So if I have a water molecule... say a bunch of water molecules here (drawing a 34 vertical line of water molecules on the board) and then over here I have just a 35 hydrocarbon (draws a hydrocarbon chain vertically next to the line of water 36 molecules), so I have a nonpolar thing and a polar thing... and then I bring in a 37 different hydrocarbon (draws a hydrocarbon chain above the two lines already 38 drawn, midway between them)... are you saying that it (the top hydrocarbon) will be 39 atrracted to one of these (the lower hydrocarbon and the water chain) more than 40 the other? 41 42 G: I would think so. 43 44 I: OK, which one? 45
46 G: I would say that that hydrocarbon (upper) would be more attracted to that 47 hydrocarbon (lower) and the thing is too is that I don't think anyone in my class 48 actually knows why that is specifically. I think we just know that we've always been 49 told they go together. So we skip the whole intermediate 'how it happens' and jump 50 to the conclusion, well, that (upper hydrocarbon) has to go to that (lower 51 hydrocarbon). But my overall understanding of why that is is pretty weak. 52 53 [00:05:40.12] 54 55 I would assume that because all that's sticking out here (hydrocarbon) is hydrogens 56 and the charge is equally dispersed throughout the molecule, whereas here (line of 57 water molecules) you have higher electron density here (oxygen end) than you 58 would over here (hydrogen end) so you create positive on this (hydrogen) end, so 59 sort of my assumption when you would say these two (hydrocarbon and water) 60 interact with each other, you'd have the oxygens forming weak but still existent 61 hydrogen bonds with the hydrogens that are sticking out from the carbons (on the 62 hydrocarbon chain). 63 64 I: These oxygens and these you mean? (pointing between the water oxygen and the 65 hydrocarbon hydrogen) 66 67 G: Yes. And then because of the electronegativity that they (oxygens) have, because 68 they have these extra electrons that are capable of forming those weak bonds, those 69 weak interactions. That was sort of my assumption and I haven't even been 70 confirmed on that. 71 72 I: Wait, so you're talking about why this (water) would be attracted to that 73 (hydrocarbon), right? 74 75 G: Right. And that's when I was saying when they were mixed together in water, 76 but then you have these (the two hydrocarbons) more next to each other, you'd 77 have these associated with each other more readily than you would this 78 (hydrocarbon and water) when this (upper hydrocarbon) is introduced but why 79 that is I'm not sure. 80 81 I: Ok. 82 [00:06:49.15] 83 84 [Brief discussion about van der Waals forces. Gavin says he expects polar‐polar 85 interaction to be strongest and nonpolar‐polar is weakest because they are not 86 alike...) 87 88 [00:08:27.08] 89 90 I: So let me ask it I guess this way... what makes any two of these things (points to 91 board) interact at all?
92 93 G: Um, it's gonna have to be you know the attraction forces of the electrons and the 94 nuclei with one another. I remember when we had you know the blackboard and 95 balloon example when you charge the balloon you know you're going to have a lot of 96 charge on it and then you're gonna have a very inert blackboard, but whenever you 97 move the balloon towards the blackboard, the electrons in the blackboard are going 98 to push away a little bit because the negative charge on the ballon is gonna force it 99 backwards becaude it's a such a solid structure that the protons themselves are not 100 going to move but electrons are more capable of moving. 101 102 I: Right ok. So in that explanation, like you're describing interactions between 103 electrons and protons which sounds like what you were saying about how opposite 104 charges attract right? 105 106 [00:09:41.19] 107 108 G: Right so we can have you know these hydrogens coming off (of the hydrocarbon 109 chain) and they're going to have a balance of charge with the carbon that's right 110 there, but then this (draws electron pairs on the oxygens on the water molecules) 111 and so even though you have a relatively stable structure you have all these 112 electrons that even though they don't really want to they are capable... so you have 113 all these weak interactions (draws dotted lines between the water oxygens and the 114 hydrocarbon hydrogens) that would form if they were close enough... [goes on to 115 explain hydrogen bonding in more detail] 116 117 I: Ok, so if you drew the same thing but can you draw 2 hydrocarbons? How would 118 that interaction look like? 119 120 G: (draws the second hydrocarbon next to the first and explain the structures)... so 121 you have a carbon which has 4 electrons and as you can tell this carbon here and 122 this carbon here are taking two of them they are sharing them, and then these two 123 hydrogens are also sharing the other two, so this generally has a charge of zero. but 124 because these hydrogens... that's where it's difficult because you say why are these 125 gonna want to interact with each other more than these (waters)... and I see what 126 you're getting at. 127 128 [00:11:26.17] 129 130 And we haven't talked about that. In physics especially. We didn't talk about these 131 individual interactions so much as the big picture, and in my chemistry classes and 132 in my biology classes at least to my understanding I don't remember us discussing 133 that, just that these (two hydrocarbons) want to be together and these (waters) 134 want to be together. But not this (points to dotted line bond between the water and 135 hydrocarbon that he had drawn earlier) even though at the same time I can actually 136 see this interaction (water‐hydrocarbon) being stronger than this one
137 (hydrocarbon‐hydrocarbon)... even though this one (hydrocarbon‐hydrocarbon) is 138 more favorable than this one (water‐hydrocarbon). 139 140 I: Gotcha.... so does that bother you? 141 142 G: Yes. Now it does :) 143 144 147 148 149 Elena Interview_02.27.2013 150 151 152 [00:13:19.25] 153 154 I: So let me ask it this way. If you were now going to say to a friend why oil and 155 water don't mix, how would you explain it? 156 157 E: Ok. I would say because oil wants to be together with other oil molecules and not 158 be mixing with other polar molecules because oil is nonpolar. And, I don't... I don't 159 really... I mean that's basically what I would say. 160 161 I: Right. 162 163 E: Because noww... cause yeah and I would say that even though the oxygen from 164 the water and the hydrogen from the hydrocarbon would have a stronger 165 interaction, the hydrocarbon chains are really long, and those would all together add 166 up to make a stronger interaction, I guess. 167 168 I: And, so from what you just said, do you feel like it's necessary to talk about 169 entropy at all? Cause you just gave an explanation... 170 171 E: Yeah, I know. It would depend on who I was explaining it to, because I now just 172 understand it more than I ever have and I've talked about it in so many other 173 classes... if I'm trying to explain it to one of my other classmates I would talk about 174 entropy. But if I was trying to explain it to someone else I wouldn't (laughs). 175 176 I: So if you were talking to a classmate, what would you say? 177 178 E: I would say that when oil is separate from water it's in its own layer, it can 179 interact more with other oil molecules and be in more different places, and that's 180 more microstates, and an increase in microstates you have more disorder and 181 more... or higher entropy. 182
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