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Everything posted by Darkblade48

  1. Indeed, liquid carbon dioxide will be quite difficult to isolate, due to the pressures needed; liquid nitrogen is better, at least you can get isolate it at standard pressure (albeit you need low temperatures).
  2. Just to let you know (I'm not sure if it's the formatting of the forums), but the hydrogens that you've drawn for propene are incorrect. And, yes, as mentioned, isopropyl alcohol is the main product due to Markovnikov's rule...
  3. I'm not quite sure of why you are investigating 1). The decomposition product (oxygen) of hydrogen peroxide is not a gas that would spontaneously decompose. 2) I'm not sure what kind of analysis technique is available to you, but in general, all hydrogen peroxide sold today contains an inhibitor and/or buffer.
  4. That might occur when you heat it to, or above, the decomposition temperature; however, that is unlikely to occur at normal STP.
  5. Just because a solution bubbles when sodium bicarbonate is added to it does not indicate that sulfuric acid is present. I could add sodium bicarbonate to a solution of copper sulfate and observe a similar bubbling phenomenon.
  6. I don't think solution of alum hydrolyze to form dilute sulfuric acid; this would be like saying that copper sulfate hydrolyzed to form dilute sulfuric acid (which does not occur)
  7. As far as I knew, the addition of salt depresses the freezing point (i.e. salt water will not freeze at 0 C).
  8. The solution may appear blue due to the fine precipitate (it stays in suspension quite easily). However, if you let it settle for a while (perhaps a day or two), you should see that there is a blue precipitate, and that the solution is not homogenous. In my experience with this kind of electrolysis, the product I get is Cu(OH)2. Since it is a hydroxide, reaction with sulfuric acid will generate copper sulfate (as well as water). Hope that helps
  9. Well, if you can alter pressure, temperature, or even run electrical discharges through helium, etc (in essence, if you have extreme conditions) you can form compounds with helium.
  10. Well, if copper was forming copper sulfate, and leaving magnesium as a precipitate, the magnesium should react with the water, forming insoluble magnesium hydroxide (a white precipitate) instead. Thus, if you had copper sulfate with magnesium hydroxide, you should have a blue solution with a white precipitate at the bottom (after you let it settle, of course). However, in my experience, the I tend to get a dirty, light blue precipitate, which then disappears upon upon addition of sulfuric acid. The solution also becomes a slightly darker shade of blue.
  11. IIRC, the electrolysis of copper terminals in a MgSO4 solution will not create copper sulfate, but copper (II) hydroxide, Cu(OH)2. This is the light blue precipitate that you observe in the water when you use a clean copper wire instead of a penny. You'd have to look up the percent composition of the pre 1985 pennies to determine exactly what the yellow precipitate was; however, I find it unlikely to be sulfur. Also, copper does not spontaneously bond with the sulfate, leaving magnesium as a precipitate.
  12. For the first question, my interpretation is that a) is correct; as that is what I was taught. I can see how b) could be interpreted as correct, however. For the second question, it is very possible for pH to be either greater than 14, or less than 0. For example, a 10 molar solution of HCl would generate a pH of -1 (HCl, a strong acid, assume complete dissociation of H+ and Cl-, you get 1 molar of protons, -log(10) (base 10) gives you -1).
  13. This definitely sounds like a homework question, so I won't be giving away the answer; however, it is possible to guide you through it. You know that the pH is 7.4 in blood; and you are given the equation for the equilibrium reaction, as well as the Ka for the reaction. From there, just make an ICE table (initial, change, equilibrium) and you can easily solve the question. Remember that pH is a measurement that is dependent on the concentration of protons.
  14. A quick Wikipedia search yielded the following: http://en.wikipedia.org/wiki/Functional_Groups Hope this helps.
  15. To find all the possible isomers of octane, simply draw out all the chemical structures. For example, 2-methylheptane, 3-methylheptane and 4-methylheptane are just some examples... From there, you can move down to hexane, pentane and butane, etc.
  16. As I mentioned previously, the 5000 litre consumption of water is assuming a LD50 of 52 mg/kg (not the higher 75 mg/kg in humans). Also, that's assuming that the water has a fluoride concentration of 0.67 mg/L and not 0.12 mg/L. If we take these new calculations into account, the LD50 would be 4875 mg, and at a fluoride concentration of 0.12 mg/L, we would have to consume 40 625 L of water in order to reach the LD50. Obviously, at such a ridiculous number, we'd die of osmotic shock long before reaching toxic doses of fluorine. According to Wikipedia (unfortunately, it's 6:49 am local time, and I don't want to bother looking up a better source at this hour), fluoride compounds are excreted through the urine, with a half life on the order of hours. Needless to say, fluoride compounds just don't have the "staying power" as some other more toxic elements (such as cadmium). Of course, fluorosis can be a potential problem, but this would only be caused by an excessive intake of fluoride compounds during tooth development. By excessive, I take this to mean much greater than the concentrations found in fluorinated water. Regarding your comment regarding attempting to stay 10^-12 below the LD50 (I assume this is what you meant by wanting to stay "x below E12 the LD50"), DrDNA; I think this is absurdly impossible. For example, the LCLO for ozone (inhalation, humans) was 50 ppm over a period of 30 minutes. It would be impossible to achieve a concentration of 5.0 * 10^-11 ppm of ozone in any given urban area (or rural area, for that matter)
  17. Yes, indeed, fluorine is an important trace element. It can bind to the hydroxyapatite found in our tooth enamel and strengthen it (for one). Since you are not staunchly opposed to fluoride in toothpaste, then I will drop my argument for the fluoride in it. However, I still believe that water fluorination is definitely an advantage. Most cities or municipalities fluorinate water at very low concentrations; for example, my city's annual water report cites that we had approximately 0.12 - 0.67 mg/L of fluorine in the water. If we take the higher value of 0.67 mg/L As stated previously, the LD50 oral for a rat was 52 mg/kg. Using this value and extrapolating for a 65 kg "average" human male, the LD50 was 3380 mg. Dividing this by 0.67 mg/L, we get 5044.78 L. Keep in mind that this is a number erring on the low side (recall that LDLO for humans was 71 to 75 mg/kg, and that my city's fluorine can be as low as 0.12 mg/L). As for tooth whiteners, I believe most of the products on the market today are peroxide based (i.e. carbamide peroxide). In essence, you are bleaching your tooth enamel everytime you brush your teeth in order to get that bright white smile.
  18. I'm not quite sure how to explain sediment depth to you; it is exactly as it sounds. It is simply how deep the sediment (i.e. dirt, soil, other debris) at the bottom of a lake/pond/other body of water. This question is not so much so a memorization question as a "thinking type" question. At a sediment depth of 10 cm, there will be an anaerobic environment (i.e. oxygen free environment). Let's keep this fact in mind while going through the options: a) Sulfide. This will likely change in anaerobic environments, as there are many bacterial species that reduce sulfur (to hydrogen sulfide) to allow the electron transport chain to proceed. b) Carbon dioxide. This is a byproduct of many anaerobic metabolic pathways, so this will not remain constant either. c) Ferric ion. Again, this will most likely change in anaerobic environments. Ferric ions are terminal electron acceptors, and thus will be used up by bacterial microorganisms. d) As mentioned above, at a sediment depth of 10 cm, there will be an anaerobic environment, and hence, the level of oxygen will be negligible, and will thus be constant.
  19. I'm slightly confused by your question; propane only exists in one conformation...?
  20. As far as mercury amalgams go, I am quite aware of the potential danger that is carried with them; however the potential risk is so low that it is essentially negligible. For example, everytime you fly in an airplane, you are exposing yourself to more cosmic radiation. Does this mean that you will should not fly in planes, lest you want an increased risk of cancer? As for the fluoride; yes, fluorides are quite nasty. Let's take a look at the LD50 orally for a rat (we'll assume this to be the method of entry, I doubt very much that you will either subcutaneous apply or inject yourself intravenously with sodium fluoride); you have listed it as 52 mg/kg. If we assume this LD50 holds true in humans, then we can assume it to be 52 mg/kg as well (this is not even true, the MSDS you posted has listed that LDLO for humans was 71 and 75 mg/kg). Assume the average male is 65 kg. At a LD50 of 52 mg/kg, you'd need 3380 mg of sodium fluoride to kill half of the tested population. Now, take my tube of toothpaste for example. It's 0.243% sodium fluoride w/v, and it comes in a 130 mL tube. If we assume that the toothpaste has a density of ~ 1 g/mL, then there would be 0.3159 g of sodium fluoride. Needless to say, this is less than the 3380 mg needed to achieve a LD50 in rats. On top of this, I don't think you'd be using the entire tube of toothpaste to brush your teeth every night... Also, toothpaste packages do warn against swallowing the toothpaste, precisely due to the inclusion of sodium fluoride; however, I have swallowed it on several occasions, and I'm not dead yet...
  21. Is water fluorination not to strengthen the enamel of teeth? Besides, not only is fluoride found in (tap) water, but a lot of toothpastes nowadays also have some degree of fluoride in them. As for mercury fillings, true that you wouldn't want to put (say) metallic mercury in your mouth, but when it is amalgamated with the various metals used in dental fillings (silver, tin, etc), I thought it was bound up quite tightly. In addition, the amount of mercury leeched from such an amalgam would be essentially negligible.
  22. I'm not quite sure where you are getting this from, but the ammonium cation (NH4+) is quite stable in itself. When a salt such as NH4Cl is placed into water, a proton does not spontaneously come off and associate with a Cl- anion. As John Cuthber mentioned, dissolving NH4Cl in water is quite dull, and no reaction takes place save for the hydration of the ions.
  23. These questions seem like homework questions, however, I'll try to provide hints without giving away the answers. By definition, an exothermic reaction is one that will produce heat. An endothermic reaction would be the opposite, it would require heat to proceed. As to why there are these types of reactions, you will have to investigate enthalpy; this will provide you with the reason why a reaction may be endothermic or exothermic.
  24. I agree with ecoli, there is a lot of information on anti-bacterial compounds. In terms of anti-bacterial soaps, most contain triclosan, which is supposed to inhibit bacterial fatty acid synthesis (it appears to be bacteriostatic). Vaccines are not anti-bacterial, per se, rather, they prime the body's immune system to recognize a certain epitope, and upon second exposure to the antigen, an immune response can be mounted much faster, and much stronger. Other anti-bacterial agents such as drugs can be bacteriocidal. I believe rifampin was bacteriocidal (it could be bacteriostatic, but I'd have to check on that), through inhibiting RNA polymerase. Other drugs like cephalosporin are bacteriocidal by disrupting the synthesis of the peptidoglycan wall in bacteria (I believe the mechanism was that it prevented transpeptidase from adding on new subunits to the existing PG wall)
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