Pub #brownchem: @alpha137
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*** LizK (gloworm4@168-92-47.ipt.aol.com) has joined channel #brownchem
LizK: Hello
LizK: hello???
alpha137: hello
alpha137: I was doing email and not paying attention.
LizK: I see, thats ok
alpha137: It was nice that you had this great trip to Paris.
LizK: I read the conversations with the other people
alpha137: Good, any questions?
LizK: OH, it was wonderful, I really enjoyed it, and even got to practice frence too
LizK: Ummm, questions, well, I didn't get all of the electronics analogys but I understood the whole diagram thing
LizK: sorry about spelling, it was french, and analogies (i think)
alpha137: The thing about electronics is that it is quite general and so can be used to make models of other things.
alpha137: The concept of feedback, even the term, is from electronics.
alpha137: Since I studied a bit of electronics it is natural for me to think in these terms.
LizK: ok, but i have just the vaguest idea of the whole electronics stuff, I had to take a technology class and we learned about resistors and circutes etc. but i don't remember any of it anymore
alpha137: In my study of electronics, from a theoretical point of view, I learned that it is really about physics, etc.
LizK: I see, and not having already had physics makes that a bit harder.
LizK: for me
alpha137: The concept of a resistor is a general one. For example, if water is flowing down a river and there is a narrowing that is an analog of a resistor.
LizK: yes,
LizK: weren't there different colors for different strengths?
alpha137: If we have two resistors we can put them in series, one after the other, or in parallel, one besides the other.
LizK: YEs, I understood the series stuff, but that was about it,
alpha137: There is a resistor color code to use as a label for the physical, electronics resistor, but we are talking about principles rather than electronics.
LizK: Yes, but i just wanted to be sure that i was thinking of the right things
alpha137: In many chemistry and physics things this resistor analogy works-that is, parallel, vs. series.
alpha137: We also have the idea of amplification.
LizK: I see,
LizK: Which is just a general idea, right, something that makes something else bigger?
alpha137: Thinking about global warming, a greenhouse gas is a temperature amplifier.
LizK: Yes
alpha137: That is, addition of CO_2 causes the temperature to increase.
LizK: and that leads back to the feedback cyc;e
LizK: cycle
alpha137: So, I was thinking that a little bit of carbon dioxide would cause the temperature to increase a little bit and this would cause the vapor pressure of water to increase as well.
alpha137: Right, that is a feedback.
alpha137: If this were all there was to the feedback "circuit" we would have a runnaway temperature increase.
LizK: YEs, Like in the flowchart, I liked that , it was very easy to understant
LizK: understand
LizK: So something has to change the tide
LizK: make it go down not up
LizK: like the CO_2 sinks or the dust particles, or clouds etc
alpha137: Right, but what? Things are very complicated.
alpha137: Each box in Ab's flow chart is a complicated system.
LizK: Yes, and there are probably lots that we don't even know exist
alpha137: As I said in one of the discussions, different links in Ab's flow chart have different times.
LizK: ok
alpha137: The idea of time here has an electronics analogy. The relavant quantity is the "time constant" for the process.
LizK: ok
alpha137: We can borrow the phrase and the idea, but do not need to use the exact electronics formula.
LizK: i see
LizK: would the formula even work?
alpha137: For the record, the time constant in electronics is 1/RC where R is the resistance and C the capacitance. And no, the formula would not work unless we made the physical analogy for R and C.
LizK: i see
alpha137: I might add, that someone has done just that!
LizK: really!
alpha137: Yes, but I do not have the reference yet.
LizK: ok
alpha137: For us, the concepts are enough and the realization that for a model we need time constants and further details.
LizK: ok
LizK: fine with me
alpha137: Reading the article by Wally, which sumarizes geological work, I think that the greenhouse problem is pretty scarry. We can let it go at that for now.
alpha137: We have considered one method of reducing CO_2 but using fuel cell and hybrid autos.
alpha137: but ->by
here is a link
to a site with information about greenhouse gases
LizK: Yes, I agree, it is very frightening
LizK: yes
LizK: I figured
alpha137: Another big issue has to do with water, the water supply and its pollution and care. Shall we discuss water?
LizK: Sure
LizK: Water is a big issue
alpha137: Water is really a special substance. Why, for example, does it disolve ions?
LizK: because it is a polar molecule
alpha137: If you have a positive charge, like Na+, and a negative charge like Cl^- the attraction energy is very great. And yes it is a polar molecule, but why does it dissolve stuff?
LizK: The hydrogen bonds? and doesn't it disolve salt because the O side is attracated to the Na and the H sides are attracted the the CL?
alpha137: Yes.
LizK: ok
LizK: YEs to what, the hydrogen bonds part or the ohter part?
LizK: ohter=other
alpha137: I guess to both.
LizK: oh good, even better
alpha137: What is the physics law that is used to describe the attraction (or repulsion) between two charges?
LizK: I don't know
alpha137: It is named after some physicist in the past. Called Coulomb's Law.
LizK: Ok
LizK: thank you
alpha137: Force = -(some constant) Q1 x Q2/R^2 where Q1 is charge 1, etc. and R the distance between 1 and 2
LizK: ok
alpha137: It is a formula determined by observation.
LizK: I see
LizK: how can you tell if it is attraction or repulsion
alpha137: Take two ping pong balls and some amber and cat fur. Rub the amber with the cat fur and charge up the ping pong balls. The balls will attain opposite chages and swing apart.
alpha137: It is an old experiment.
alpha137: Back then they did not have ping pong balls, but pith balls made of cork.
LizK: I see, but i meant from the formula,
LizK: if the answer is negative it is ? positive implies something different ?
alpha137: Well, from the formula if Q1 is a Chlorine atom in NaCl it would be negative.
LizK: yes
alpha137: And sodium plus would be positive.
LizK: yes,
LizK: But the overal force
LizK: should be pos- yes
LizK: to be attraction?
LizK: so that a neg force would end up with repulsion?
Quite right. A negative force would be a repulsion. That is, one of the charges (it does not matter which you pick) "feels" a negative forced due to the other charge and that is a repulsion. This would be the case for an H^+ and a Na^+ ion. A positive force is an attractions as between Na^+ and Cl^-.
LizK: I think i understand- are you still there?
LizK: oh, I forgot, THank you very much for the book
alpha137: Yes, like charges repell so that if Q1 and Q2 were the same sign then the force on one of them would be negative
LizK: ok
alpha137: A little math will convert this force formula to one for potential energy.
LizK: ok
alpha137: V = (constant) Q1 x Q2/ R
Here is a slightly better view of the equation
LizK: ok
alpha137: The point is that we could estimate the energy needed to seperate NaCl into two ions very far apart.
alpha137: We just need that constant.
LizK: i see
alpha137: Actually, we have a grain of salt, not a molecule.
alpha137: We have a crystal of salt.
LizK: yes
alpha137: If we take that fact into account then the energy needed to seperate NaCl (s) into its ions is about 861 kJ/mol
LizK: ok
alpha137: Where does all that energy come from?
LizK: heat? bonds?
alpha137: Well, no. I am doing all this just to make the point of how remarkable water is.
LizK: The water?
alpha137: Yes, it is the water.
LizK: ok
alpha137: You mentioned that water has hydrogen bonds and is a polar substance.
LizK: I see, so the water is like a catalyst for breaking the ionic bonds
LizK: yes to your last stmmt
alpha137: Yes, kind of like a catalyst, but more like a mediator.
LizK: ok
alpha137: The pith ball, or ping pong ball formula was for charges in a vacuum.
alpha137: We have charges in water.
LizK: but the earth is n't a vacum
LizK: yes
alpha137: No, the earth is not a vacuum, but has an atmosphere. The properties of this atmosphere have to be taken into account in the formula.
alpha137: However, the formula was for a vacuum!
LizK: yes
alpha137: Well, it was for a vacuum depending on what we say that "constant" is.
LizK: So the formula needs to be changed!
LizK: ok
alpha137: Yes, the formula needs to be changed depending on the environment of the charges.
LizK: ok
alpha137: The constant goes like (constant) = 1/(4*pi*epsilon_o) where epsilon_o is a Greek letter that stands for the dielectric constant and the zero _o is for vacuo.
LizK: ok
alpha137: The dielectric constant for various substances can be measured an is in tables and can be looked up.
LizK: ok
LizK: I'm glad
alpha137: For water the dielectric constant at room temperature is about 80 epsilon_o
LizK: ok
alpha137: That means that that formula gets to be divided by 80.
LizK: i see
alpha137: That means that in water the 861 kJ/mol becomes 10.8 kJ/mo.
LizK: ok
alpha137: 10.8 kJ/mol we can get from the surroundings.
LizK: ok
LizK: Thats a lot easier to get than 861kJ/mole!
alpha137: The reason that water gives us this big dielectric constant and hence this large reduction in the energy needed to seperate charges is because of its polar and hydrogen bond nature.
LizK: ok. it all goes back to that
alpha137: You can think of two charges with water in between with negative parts of water towards Na^+ and positive parts towards Cl^-. This lessens the Coulombic force!
alpha137: This is the wonder of water.
Here is a illustration of the Coulombic attraction between sodium ion and a chloride ion in vacuo.
LizK: i see
LizK: water is pret
LizK: oops, I was saying that water is very cool
alpha137: It really is.
Here is an illustration of the Coulombic attraction between Na^+ and Cl^- mediated by water. You can see how the water molecujles act as shields between the chloride and the sodium ion.
alpha137: You can apply these ideas for any substance you might find in water.
LizK: thats good
alpha137: For example, a service station's gas tanks leak into ground water.
LizK: thats not good,
alpha137: Gasoline is a mixture, but considering it to be octane, would octane dissolve in water?
LizK: I think so, maybe becaue the hydrogen sides might be attracted tgo the oxygen of water, but then maybe not. but it would still be a bad situation
alpha137: You are on the right track.
LizK: tgo = to
LizK: ok
alpha137: Octane would not be very soluble in water, but some would dissolve.
LizK: i see
alpha137: That small amount would not be healthy.
LizK: no, and moreover, even if it was just mixed with the water, that would be bad
alpha137: If you notice you might see many service stations digging up their tanks and replacing them.
LizK: for this reason?
alpha137: Suppose we have a molecule like TCE (trichloroethylene). Would it dissolve in water?
alpha137: Yes, service stations are replacing gas tanks because they leak into the water supply.
alpha137: Which would be more soluble in water, TCE or octane?
alpha137: Interested people want to know.
alpha137: LizK?
alpha137: Hello?
*** Signoff: LizK (Ping timeout)
*** LizK (gloworm4@168-92-47.ipt.aol.com) has joined channel #brownchem
LizK: hello again
LizK: I don't know what happened
LizK: That was very strangw
LizK: strange
LizK: Are you still there??
alpha137: Yes, I just stepped out of my office
LizK: hello????
LizK: ok, I got disconnected, I'm not sure why
LizK: but it is all better now
alpha137: There was no activity and so I went to show off my new apple powerbook
LizK: I see,
alpha137: It is a fancy machine running at 250 MHz with a 13 inch screen.
LizK: What was the last think that I said
LizK: Wow!
LizK: how much does it weigh?
alpha137: Anyway, I had a couple of questions and I am not sure you received them.
LizK: ok. shoot
alpha137: The thing is not light, weighs 7 lbs.
LizK: oh, thats too bad,
alpha137: My question was does TCE (trichloroethylene) dissolve in water?
LizK: But with a screen that big, it couldn't be very light
alpha137: And the next one was: which is more soluble in water TCE or octane?
LizK: YEs, I got that, I said I guessed, based only on the fact that Cl is very polar, and that ethyl alcohol dissolves in H2O that TCE would as well
alpha137: The 7 lbs is not so bad considering all that comes with this machine.
LizK: Since octane doesn't really dissolve in water, I thought maybe TCE
LizK: But I typed all that in- did you not get them??
alpha137: No, I did not get your answers.
LizK: That is very strange
alpha137: In anycase, you are right the TCE would be more soluble in water than octane.
alpha137: TCE is a common solvent used in industry.
alpha137: It is a common pollutant of water supplies as well.
alpha137: Would TCE be more soluble in water than alcohol?
alpha137: By the way, on my screen it said Signoff: LizK (Ping timeout), but you remained on the user list!
alpha137: You gone again?