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blackhole123

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About blackhole123

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  • Birthday 07/15/1978
  1. Thanks. Don't worry, I have no intention of letting my grades slip at all. I know that I definitely need to do my research before applying as well. School name isn't everything, and I'd like to find a good mentor to work with.
  2. I am currently a chemistry major in my junior year. I have a 3.95 overall GPA (one B freshman year) and a 4.0 in chemistry. I have been doing undergrad research since the beginning of my sophomore year. Last summer I did an REU (if you don't know, it is a 10 week long research program for undergrads). Hopefully I will be doing another REU or internship this coming summer. I have already taken one graduate level chemistry class and got an A. I have my name in one published paper so far (not first author). I feel like I am doing everything that I can possibly do to bolster my chances for getting into a great PhD program, but part of my is really worried that it isn't going to pay off. How badly will it hurt me that I currently go to a tier 2 school? It is a large state school with a good chemistry program, but it is nowhere near the types of places I have in mind for grad school. I just want so badly to get into a big name, top ranked school for grad school and I have been working my tail off to make sure it happens. I just want to know if I really have a shot or if it is sort of a random chance type thing. I really feel like there isn't anything more that I could be doing to show that I deserve acceptance to a top ranked program, but yet I feel like I am still going to receive rejection letters and be left wondering why.
  3. So I'm degasing a solution in a glovebox. The way we did it is get a rubber septum that can cover the bottle opening. We stuck a needle through the top of it, as well as a glass tube with a porous end. We used the needle to create a vacuum in the bottle by hooking up it up to a pump. The glass tube is submerged in the solution, but is stuck through the rubber to be the only opening into the box. The argon from the glovebox then flows down the glass tube and out the frit at the bottom, degassing the solution. I can't figure out why the gas would be sucked down the tube. Sure there is a vacuum in the bottle, but the tube opening is submerged. It doesn't know or care that there is a vacuum above it. The only part of the glass tube that experiences vacuum is the long tube part without any openings. So how is the vacuum sitting above the liquid making the gas flow into the tube which has it's end submerged? Obviously it works for some reason, I just don't know why. This has been bugging me, thanks.
  4. 1) Yes only the last contributed to the excess. 2) So we are right that to get excess permanganate, you subtract excess oxalic acid from the amount of oxalic acid from the 100mL that we added? 3) So the permanganate from the original 50mL minus the excess determined from (2) equals the nitrite? Thanks again.
  5. Potassium permanganate (KMnO4) is used to determine the actual concentration of standard solutions containing the nitrite ion. The permanganate ion reacts with nitrous acid according to the following reaction. 2 MnO4- + 5 HNO2 + 5 H+ = 2Mn2+ + 5 NO3- + 3 H2O Pipet in order 50.00 mL of standard KMnO4 solution, 5 mL concentrated H2SO4 and 50.00 mL of NaNO2 solution into a glass-stoppered flask. Making sure that the pipet tip is submerged below the surface of the permanganate-acid solution while delivering the nitrite stock solution. Shake gently and warm on a hot plate to about 70oC. Discharge the permanganate color by successive additions of 25.00-mL aliquots of the 0.025 M oxalate solution. Back-titrate the excess oxalate with the standard permanganate solution to the faint pink end point. Run a water blank and make the necessary corrections. Calculate the concentration of NO2- in the stock solution. Calculate NO2 in stock solution. And here is the formula for KMnO4 reacting with sodium oxalate (N2C2O4): 2 MnO4- + 5 H2C2O4 + 6 H+ = 2Mn2+ + 10 CO2 (g) + 8 H2O My two partners and I have been attempting this for like the past two hours. We have calculated it a ton of different ways and always get a different answer. So basically, first you have a solution with excess KMnO4. Then you add oxalate so that you have excess oxalate. We added 100mL of .025M sodium oxalate. Then you titrate the excess oxalate away with KMnO4. So I know how much excess oxalate was there was based on how much KMnO4 was used to titrate at the end. Now what? Please help, we have been working on this for so long and we can't continue with the lab until we figure out the concentration of the stock solution. Numbers aren't really important, I can do those on my own. Here is a thought I had... since KMnO4 reacts with nitrite, that means that the original KMnO4 in the solution reacted with the nitrite. So there was less KMnO4 than if there was no nitrite. So: Original KMnO4 - Nitrite = excess KMnO4 So Mol Nitrite= Original KMnO4(we know this) - excess KMnO4 (after multiplying by 5mol NO2/2mol KMnO4) My partner seemed to think that the excess KMnO4 was equal to: Total oxalate- excess oxalate = corrected oxalate= excess KMnO4 (again, after applying stiochiometric ratios) Using this, we got a number that was sort of close to the expected value. We got like .47g/L when it was supposed to be like .41g/L. That still seems wrong to me, but it could be right. I just don't get how to come up with the value of excess permanganate. PLEASE HELP, we are falling behind. Thanks! EDIT: I think I may get his reasoning. When the last titration is done, you have all of the oxalate in equivalence with the excess permanganate plus the permanganate you added during the titration. So if you get rid of the excess oxalate you now have corrected oxalate in equivalence with the excess permanganate (excess as in the permanganate that did not react with nitrite). So convert corrected oxalate moles to moles of permanganate and that is the moles of excess permanagate. Then use my nifty formula: NO2= Original permanganate - excess permanganate So we did do it correctly???? Eureka! (I hope)
  6. I'm a second year chemistry major and I love it, but I had a couple questions that I thought some people here could clear up. A lot of my friends are pharmacy majors. They are going to go to school for 6 years, get a pharm D, and then go out and make $100,000 a year. I'd be a chem major no matter what, but how much does a fresh PhD in chemistry usually make right away if they went into industry? The internet tells me $66,000, is that about right? It just seems like I'm going to have to spend more time dealing with more difficult subject matter and have to write a thesis and everything, and they will make more than me, at least initially. How long does it usually take to get a PhD? 3 years is what most programs are, but I just can't see most people getting a PhD in chemistry after 3 years in grad school. Most of my TAs have already been there for longer than that. I think I like inorganic chemistry. I haven't taken the course yet but the undergrad research I'm doing is all about inorganic synthesis and I really like learning about crystal structures, XRD, etc. But whenever I think of someone having a successful career in chemistry, I think of going to work for a big pharmaceutical company, which would probably be organic. Am I limiting myself by 1) getting a degree in chemistry, not chemical engineering, and 2) not going into organic (which seems to be the main option if you aren't an engineer)? I'd love to do research at a university, but my ultimate goal is to go into industry for a few years and then go back and teach. What exactly do you DO on an average day at work as a chemist? Sit down at a table and start making hypotheses? In the lab most of the time? Thinking about having a job is so intimidating right now. To go back to the pharmacist example, it seems like what they do is pretty prescribed (pun intended). But as a chemist, you actually have to actively contribute to the company and come up with new ideas and stuff! Yikes! I'm sure everyone feels this way at my level, but wow am I scared to have to do that. I'm at the top of all my classes so I'm not worried about being smart enough (well, maybe a little), it just seems like so much would be expected of you. And again, those damn pharmacists (damn them) are going to make so much more than me. I just researched what the average professor makes and its around $40,000! What the hell?! I could make that much being a manager some random store, but instead I need 7 years of education (and not everyone can even do it, the material is hard) to get to that point? I'm going to do what interests me regardless, I'm just curious. It's pretty early to be planning for a PhD and being a professor, but again, I'm just curious.
  7. First of all, I'm an undergrad and am currently do undergrad research. So today I was chatting with the graduate student I am working under and somehow the subject of Harry Potter came up and I mentioned that I am going to see it on Thursday night. She then told me that she never read the books because a church elder told her not to. I was really taken aback. Here is this PhD candidate who I know to be an excellent scientist, not reading a childrens book because their minister told them it was bad. I just don't understand how scientists could be so rational and empirical about everything during their work, and then somehow forget all that when it comes to religion. It's just such an irrational thing for people whose lives are defined by rationality and evidence.
  8. So this is my first semester doing undergraduate research, and I'm very exited about it. We have been doing a certain experiment for a couple months now and the first big hurdle we are facing is getting a pure product. Basically, we are trying to make a substance and then analyze it by XRD. The problem is that we are getting a lot of impurities in the final product. I don't want to go into too much detail, but basically there are two steps: adding NaOH to a substance, and then oxidizing it. So far we have tried doing the reaction under nitrogen, and instead of adding the oxidizing agent as a powder we dissolved it and added it at a constant rate. Still there are impurities. I know I'm being very vague, but I was just wondering if anyone had any general suggestions for getting pure products. I'm just working under a grad student, but I know it would impress them if I could come up with a suggestion to improve the experiment. So far the only thing I can think of is using a different oxidizing agent, but I'm guessing this wouldn't work for some reason that I wouldn't understand. Most of the chemistry involved is way over my head at this point in my education.
  9. =Lets say you titrate a weak acid, HA, with a strong base, NaOH. Now, before the equivalence point, the pH is calculated like a buffer because HA + OH- -> A- + H2O. So you have a mixture of a an acid and its conjugate base. My question is, why doesn't this act like a neutralization reaction like a strong acid and strong base? In order to get OH- you have to dissociate NaOH, so you also have Na+ in solution. Why doesn't the Na+ react with the A- to form a salt like a strong acid and strong base would? I'm also confused about buffers in general. You have an acid and its conjugate base... why don't they react? How can they coexist in solution? Help, I seem to have a fundamental misunderstanding of acid-base chemistry! EDIT: WOW I'm dumb. I've been stressing over this for hours, thinking I didn't understand chemistry anymore. But obviously, the A- is in solution so its not going to form a precipitate because salts dissociate in water. Na+ is just a spectator ion. Still not totally sure on the second question though. Well, actually I guess they couldn't really react and change pH. If HA reacts with A- it would just form another A-....
  10. Thanks, I think I see my mistake. I was thinking of "a"'s sign as meaning whether it was accelerating or not, i.e. -9.8 meaning it is decelerating and positive meaning it is accelerating, hence even though I considered down as negative, I had a as +9.8 since it increases acceleration when it is going downward.
  11. Makes sense, and then I apply whether is is positive or negative based on whether it is increasing or decreasing? In these problems what should a be, 9.8 or -9.8? Does that change based on whether it is going up or down? Why don't I just post the whole problem: To test the quality of a tennis ball, you drop it onto the floor from a height of 4.00 m. It rebounds to a height of 2.00 m. If the ball is in contact with the floor for 12.0 ms, what is its average acceleration during that contact? The answer is 1.26x10^3m/s^2 So I got the answer I already posted for descent, 8.85, then figured out the velocity for ascent, which is 6.26. Then the average acceleration is change in velocity over the time it was in contact with the floor. In order to get the right answer 8.85 had to be negative so you could have: (6.26+8.85)/.012=1.26x10^3. One of those velocities has to be negative (and it should be descent velocity), no matter how you cut it, and you have to take a square root to get both of them. I guess because velocity is the derivative of position, and if the graph of the function is decreasing then the graph of its derivative is negative.
  12. I am using the equation for constant acceleration to find velocity. v^2=v(initial)^2+2a(x-x(initial)) Dropping a rock from 4 meters to the ground. Initial velocity is 0, a=9.8, and displacement is -4. So v^2=2(9.8)(-4), and it SHOULD equal=-8.85m/s (I know this is the correct answer, I already got it right on my homework). The velocity should be negative. But obviously my above answer is impossible because you can't take the square root of a negative. When using these constant acceleration equations I make the sign in the above equation negative if it is going upward, and positive if it is going downward. Do I apply the negative sign after I solve, to show the direction? That just doesn't seem right. Help!
  13. So, I basically blew off the last couple weeks of calc 2 because they dropped the lowest test grade so I could skip the final test. Thus, I missed the last half of infinite series. Will I need to teach it to myself for Calc 3 over the summer? "Geometry and vectors of n-dimensional space; Green's theorem, Gauss theorem, Stokes theorem; multidimensional differentiation and integration; application to 2- and 3-D space." There is the course description.
  14. I was using a .45uM filter on a solution, and while water could pass through it quite easily, air does not pass through at all. If you try to pass air through the filter it is impossible. So, does that mean that water is smaller than all the molecules in air, or is it something else? I would have thought something like O2 would be smaller than H20.
  15. I'm not sure how to say this... Is there difference between the cathode and the anode that is there without the actual substances powering the battery? The positive and negative charges of the different electrodes are because of the spontaneous flow of electrons (in a voltaic cell). But don't you have to connect specific wires to specific parts on a voltmeter for it to record? So, if you are making an electrolytic cell and you connected it, would it spontaneously go until you applied an outside source of electrons to reverse the reaction? In other words, the cathode and the anode can only be defined AFTER the reaction has started, right?
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