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Everything posted by UC

  1. Substitute every word about dowsing or divining for something about homeopathy, telephone psychics, prayer, etc.
  2. Provided strong base, of course. Heat just makes it go much faster. Even cold ammonium nitrate solution and cold sodium hydroxide solution would have stunk like ammonia as soon as mixed together
  3. UC

    Pchem dump

    Start: [math] dU=TdS-PdV [/math] Divide across by dV and hold T constant. [math] (\frac{\partial U}{\partial V})_T=T(\frac{\partial S}{\partial V})_T-P [/math] Use the maxwell relation [math] (\frac{\partial P}{\partial T})_V=(\frac{\partial S}{\partial V})_T [/math] to get: [math] (\frac{\partial U}{\partial V})_T=T(\frac{\partial P}{\partial T})_V-P [/math] Starting from [math] PV=nRT [/math], take the differential form and hold V constant: [math] d(PV)=d(nRT) \rightarrow VdP=nRdT \rightarrow (\frac{\partial P}{\partial T})_V=\frac{nR}{V} [/math] Substitute that in to get: [math] (\frac{\partial U}{\partial V})_T=\frac{nRT}{V}-P [/math] Simple rearrangement of the ideal gas law gives the value of the right side of that equation: [math] PV=nRT \rightarrow P=\frac{nRT}{V} \rightarrow 0=\frac{nRT}{V}-P [/math] So, overall: [math] (\frac{\partial U}{\partial V})_T=0 [/math] [Valid only for ideal gases]
  4. MS uses incredibly tiny amounts of the substances involved, so there's no issue. The worst that happens is that the sample decomposes or fragments. The ionization can occur by a large number of processes, some of which are very gentle to the molecules (Things like MALDI work on giant proteins without destroying them). The most common is probably electron impact, which tends to fragment the parent ion to a large extent, allowing structural information to be determined. It is possible to run a negative ion MS, but that requires atoms like halogens to be present. m/z analyzers vary from standard quadrupoles, magnetic sector analyzers, time-of-flight (TOF) tubes, and the holy grail being ion cyclotron resonance. Quadroples are quick-and-dirty and work well enough on small molecules.
  5. wouldn't a naked [ce] ^{62}Ni [/ce] nucleus do better? Or would increasing the atomic number merely start to give diminishing returns?
  6. Can you smell ammonia coming off of a cold solution of the unknown salt mixed with a little NaOH, or do you have to heat to smell it? It hydrolyzes just like any other amide, but that won't happen with cold, dilute base. The condensation to cyanuric acid only occurs when molten, so you solid is almost surely just carbonate and leftover hydroxide.
  7. It's urea. The insoluble white stuff is cyanuric acid, melamine, any of various intermediates between the two, or some ungodly polymeric crud. The fumes while heating were probably mostly ammonia, but if you applied a lot of heat, you could be getting isocyanic acid (HNCO, not cyanide) as well. It's being used in cold packs because it works about as well as ammonium nitrate and is less hazardous (and can't be used for pyro).
  8. Hydrosulfite (dithionite) is not the same as bisulfite. Perhaps you are thinking of metabisulfite, which is a dehydrated form of bisulfite. The problem is that we're dealing with 60% acetone in solution, and producing the bisulfite adduct requires adding water. If you use enough water that the complex is filterable, you are going to be left with very dilute ethanol solution, and the distillation thereof will leave you with the azeotrope at best. http://www.chemeng.ed.ac.uk/~jwp/procalcs/procalcs/mixtures/nonideal/slides/data/acet-eth.gif That chart shows no azeotrope or funny business of any kind. Plain old fractionation should yield pure ethanol and pure acetone. Consider using a better column (is yours insulated and is it packed or a vigreux?) or making sure your thermometer is properly calibrated.
  9. Oh, they just mean an arbitrary solution containing a bunch of it. It's just the convention to speak about it as if it's one thing when discussing functional groups and pKa, etc.
  10. A Pka value is not a pH value. Both, however are equal to [ce] - log_{10}[X] [/ce] where X is the Ka for pKa and X is the hydrogen ion concentration for pH. Here is the Henderson-Hasselbalch Equation: [math] pH=pKa+ log_{10}([A^-]/[HA])[/math] In this problem, we need to treat the -SH group as a weak acid that can lose it's proton. The anion form is represented by [ce] [A^-] [/ce] and the sulfhydyl is represented by [ce] [HA] [/ce]. Technically, the brackets indicate concentration, but since you're only interested in the ratio, it's irrelevant whether the solution is 1M, 10M or 0.005M. They've given you the pH and pKa values to plug in. Then you just need to remove the [ce] log_{10} [/ce] part of the term to get the ratio of anion to sulfhydryl. I don't understand what you mean by "how can an equilibrium reaction occur?" [ce] R-SH <-> R-S^- + H^+ [/ce] is an equilibrium reaction. The equilibrium constant represents the tendency toward the right or left of that equilibrium arrow.
  11. Here's a "snapshot" of one of the resonance forms of the ion. As you can see, there is a quaternary nitrogen present. If you use Huckel's rule, I believe that you will find this is an aromatic ring, and the positive charge is delocalized for that reason.
  12. Whoop de freaking doo. Welcome to all of chemistry. Would you like us to "beware" the other 6 million compounds that are oxidizing agents? What about oxygen itself? And what about reducing agents that can combust violently in the right conditions? Don't you live in a house? That's made of wood! It's HIGHLY flammable! Humanity needs one big warning label for absolutely everything: "Don't be an idiot." and then we let the Darwin awards weed themselves out. What about scissors? I could hurt myself with those too. Or breathing. The oxidative damage will eventually kill me. Driving a car is pretty suicidal too, if you think about it.
  13. Water vapor and ammonia are not ideal gases. Ideal gases make the assumption that there is no interaction at all between the gas molecules. This is only a model (a flawed one for most cases) but is a good approximation of the noble gases and things like nitrogen or hydrogen, especially at low pressures and high temperatures. Dimethyl ether does not have a hydroxy group. The hydrogens that it possesses are bound to carbons and are essentially nonpolar. Ethanol, however has an OH group, which is polar and can participate appreciably in hydrogen bonding. Think about it. Benzene has hydrogens, but it won't dissolve in water, which has oxygen lone pairs. If the benzene hydrogens could participate in hydrogen bonding, dissolving in water would be quite favorable, but that is clearly not the case. The enthalpy of vaporization of a liquid represents the energy needed to counteract all the IMF in the liquid state added to the energy needed to expand the resulting gas to it's final volume. For liquids that H-bond, the intermolecular forces represent the vast majority of the energy needed.
  14. The javagamer, it liesssssssssssssssssssssssss. ydoaPs can't be trusted with mop duty, much less admin powers.
  15. Safe is a relative term. 30% HCl fumes, and the fumes will rust anything made of steel in the same room as it. The containers they sell it in (hardware store muriatic acid) *do not* contain the fumes properly. It can cause pretty nasty acid burns if you get it on yourself, damage stainless steel, aluminum, steel, copper, brass, etc, and will choke you pretty nicely if you catch a good whiff of the vapors. Unless you have goggles, gloves, and good ventilation, don't use it. Some proper labware is in order. Pipettes, beakers, and glass stirring rods. You can't just slosh it around like vinegar. You need to store it properly, and glass bottles with teflon lined caps are a good choice, as it will damage some plastics. Something like this is ideal: http://cgi.ebay.com/Lab-Glass-Amber-Solution-Bottles-1-liter_W0QQitemZ140351540198QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item20ad9a8be6 It becomes moderately safer if you dilute it with 2 parts water, so that the fuming is minimalized, but is still not to be taken lightly.
  16. The easiest way is to make an ester and hit them with stoichiometric DIBAH (diisobutylaluminum hydride). Or you can reduce them to the alcohol (LiAlH4, B2H6*THF, or the acid chloride with NaBH4) and then use PCC or PDC. Or convert the alcohol to the halide, treat with silver nitrite (for best yields. lower yields are obtained with alkali nitrites) and seperate the mixture of alkyl nitrite (generally the minor product) and nitroalkane. Use the nef reaction to cleave the nitroalkane to an aldehyde. You'll have to do some research, because it works decently with some alkyl carboxylates and horribly with others (and very well with benzoic acids), but the Stephen aldehyde synthesis takes a nitrile to the aldehyde by treatment with anhydrous SnCl2 in ether followed by aqueous quenching. There are a number of ways to make the nitrile from the acid. http://en.wikipedia.org/wiki/Stephen_aldehyde_synthesis
  17. There is no easy way to do the conversion between the two. Since intermediates involving a carbocation are more stable for a secondary position than the primary position of n-propanol, interconversion is not favored. Reagents that generate a primary alcohol are quite expensive. You're better off seeking out some commercially available source.
  18. Just a guess- Cheapo uncoated off-brand acetaminophen tablets are not hard to come by and it's relatively easy to recrystallize. The fillers and binders are only a small portion of the tablet weight and are generally insoluble in most solvents. Aspirin can be recrystallized in a similar manner, using hot acetone to extract the tablets. Slow evaporation gives large, transparent crystals in my experience.
  19. Use a different acid. You risk making bis-(2-chloroethyl)ether if there is any diethylene glycol contaminant around. This is an analogue of sulfur mustards, and while not nearly as nasty, is still nothing you want to be dealing with. Dioxane is probably better made from diethylene glycol, by reaction with hot sulfuric acid, with continuous distillation of the product, analagous to the production of diethyl ether.
  20. What functional group is R-NH-C(=O)-R? It undergoes characteristic reactions with strong bases and acids. Google, grasshopper.
  21. You should visit us on IRC some more. Azure actually misses you....I think....or misses harassing you....whichever. At any rate, come back.

  22. Are you sure that this is not a thermometer issue? Is the thermometer of the correct partial immersion and placed appropriately with regards to the still head?
  23. Cupric chloride is a fine etchant in it's own right. In fact, if you prepare an etching bath of it, and continue to add HCl, you can simply restore it by bubbling air through the mix. I believe that Ferric chloride may be restored the same way, but I'm not sure how readily the air oxidation proceeds.
  24. Mutations are the ONLY source of new genetic material. Mutations are heritable, even though they may not be expressed. If the DNA being transferred to the offspring has a miscopied base pair, it doesn't vanish because the other parent didn't have it. It's still there. Very few features have "Mendelian expression" that you seem to be stuck on. Cumulative mutations over very long periods of time can result in the formation of entirely new structures, proteins, etc. Most mutations will be deleterious, and if natural selection is allowed to function, they will be "weeded out." Those that do not give an advantage are passed on at an average rate, where they can compound with future mutations. Those that convey a distinct advantage to reproductive fitness are passed on readily. Smaller numbers of mutations are unlikely to accomplish the formation of new structures, but can easily turn off normally expressed genes, or set them into "overdrive." Cancer relies on combinations of both, but these mutations (just based on probability) are often not in the reproductive cells, and many occur after childbearing years. In this case, they are not heritable.
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