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Everything posted by woelen

  1. Both discrete and 'continuous' mathematics will remain important in the future. Many physics problems are formulated in terms of 'continuous' mathematics. Numerical solutions of course essentially are discrete, but given high enough granularity, we may regard the outcomes as 'continuous'. Just look at it like water. Water looks very continuous, but when zooming in, you finally end up with discrete entities, the molecules of water (and beyond).
  2. This piece of software may be of great help to you. It is a computer algebra system with a lot of number theoretic functions, including all kinds of primality-related things, with a very easy to use programming language (called GP), in which you can program all kinds of things. You also can give simple statements for direct calculations: http://pari.math.u-bordeaux.fr/ Default precision can be changed to virtually unlimited precision.
  3. Yes, but it won't give you sodium metal.
  4. No, that is not the reason of high prices. Many industrial processes use extremely toxic and corrosive chemicals in intermediate stages. The real reason for high prices are manyfold, including: 1) Difficult processes, expensive equipment, energy intensive. 2) Profit stacked on profit stacked on profit .... Comapny A makes 100000 kilos of a chem, and sells this to a bulk reseller. The bulk reseller splits the chems in drums of 25 to 100 kilo. The company, buying these drums splits up in packages of a kilo or so, and the final outlet sells quantities of 500 grams or even less. All these things require transportation, handling, and each party wants its profits. 3) High purity demands. The labs (and also the individuals) usually obtain the chemically very pure material, which is much more expensive to make than the raw material. E.g. an extra recrystallize-step may be needed, and that adds a lot to the cost.
  5. BP, based on K2SO4 is as energetic as a dead dog.
  6. Think of it as your hands. They are very similar, but they are non-overlappable. The two hands are mutual mirror images. Indeed, each C-atom with 4 different groups attached to it is a chiral center. In more complicated molecules, it may be quite hard to find all of them, usually they contain multiple chiral centers.
  7. I can imagine that they can exist for a long time if they are VERY VERY dilute. The same is true for hydroxyl. Astronomers have found clouds with a large percentage of hydroxyl, but these clouds still have a lower density than the best vacuum we can make on earth. This kind of molecules are VERY reactive, but as long as they do not meet anything, they can exist.
  8. First show your own efforts. I am willing to help you solve these questions, but I'm not willing to spoonfeed you. Think of what reaction products there will be. Apply rules about common molecules and reactions (e.g. oxygen, what is the common molecule for this element, metal displacement reactions, common precipitates, etc.). These four questions require knowledge of different parts of the subject of chemistry.
  9. Yes, the remaining mass is in the CO2. There is conservation of mass (in fact even more specific, there is conservation of each element).
  10. Good to know that it comes from the latin word for "beyond". Although I still think some per-names are bad, I also use them, simply because everyone does. If I am talking about trioxonitrate (V) and dioxonitrate(III), then most people will stare at me.... Sometimes, these names are used though. I have made a complex like K3[Cr(C2O4)3] and I certainly would not call this potassium chromium oxalate, because the oxalate is really attached to the chromium. This must be called potassium tris-oxalato chromate (III). Two other common examples are potassium hexacyanoferrate (II) and potassium hexacyanoferrate (III). So, for non-oxo anions, the use of these IUPAC names is more wide-spread.
  11. To my understanding the "per"-prefix initially was used for peroxo-groups (-O-O-), but in those times the clear distinction between oxidation states, peroxo groups and so on was not well-developed. Just to show the flawed use of "per" in many common names: We have (I only draw one resonance extremum): [-O-N=O](-) ---> nitrite [-O-N(=O)2](-) ---> nitrate [-O-O-N=O](-) ---> pernitrite I made the pernitrite once. It is fairly easy, make an ice-cold solution of sodium nitrite and an ice cold solution of dilute nitric acid or sulphuric acid. Then drop ice-cold hydrogen peroxide (5% or so) in the solution. The solution turns red, but only for a short transient time. The red color is due to the pernitrite. So, there are two possible ions NO3(-), with very difficult chemical properties. Using the old naming scheme both would be called nitrate. So, in the sense of "more than the usual amount of oxygen", the prefix "per" would be OK, but I think that this is flawed. E.g. MnO2 is called manganese peroxide, where I live. Don't you think that is flawed? There is no peroxo group in it at all. The compound BaO2 is called barium peroxide, and that is correct, because it really contains a peroxo-group and with water it reacts to Ba(OH)2 and H2O2.
  12. Please keep in mind that this is a forum. Of course, jdurg may give you his address, if he wishes and you may have private communication, but I personally think you will have more response by using the public forums. But if you want to contact any person in a private way, just send a PM (click the private messages link at the top right of the forum page). No mail needed, PM's are really private, not even I as a moderator can read other PM's than my own (the ones I received and the ones I sent), so feel safe to use PM's.
  13. If you can do this for acids and bases, then you can also do it for reductors and oxidizers. With acids and bases, you are equalling H(+) ions and/or OH(-) ions on both side of the equation (exactly neutralizing). Now you do the same for electrons, transferred in a redox reaction. Example: redox between sodium sulfite and potassium permanganate in sufficiently strong acidic medium. KMnO4 : Oxidizer, Mn going from +7 to +2 oxidation state, 5 electrons gained. Na2SO3: Reductor, S going from +4 to +6 oxidation state, 2 electrons lost. In order to have electron balance on both sides, you need 2 'molecules' of KMnO4 for 5 'molecules' of Na2SO3. The rest of the task you can do yourself, just proceed as with acids/bases. I'm not sure about GEW. It is an old-fashioned way of expressing things, IIRC it stands for normality (number of mols of electrons per unit solution, notation N), e.g. 1 M KMnO4 is 5N KMnO4.
  14. A very rewarding and easy to perform experiment is the making of a simple cyanotype, using daylight for exposure of the ferricyanide/ferric citrate mix. This is non-toxic and can be done by the pupils/kids.
  15. I'm not sure what it is, but I don't think it is finely powdered Al or Mg. I have some of those powders and for sure, they usually don't ignite by simply blowing them in the air. I suspect that the persons, who did this trick still had some source of ignition in their hand. I know this kind of tricks from magicians shows and they use some flash-like powder, and they have a tiny sparking device in their hand.
  16. What John is telling about the -ous and -ic ending is also true for -ite and -ate. When only one oxidation state is known of a compound, then the name ends in -ate, e.g. CO3(2-) is carbonate. Unfortunately, in the past, numerous errors were made, in interpreting the structure of compounds and now we are left with a whole bunch of crappy names. We have SO3(2-), SO4(2-) and SO5(2-). These are called sulfite, sulfate, and persulfate. This is quite OK, the SO5(2-) ion has structure [-O-O-SO(=O)2](2-). It contains two oxygen atoms in a row, and hence it is called a per-compound. We also have ClO2(-), ClO3(-) and ClO4(-). Here, they are called chlorite, chlorate, and perchlorate, but here things are wrong. In fact, what is called perchlorate, could better be called chlorate, because it is the highest oxidation state for chlorine (+7) and there is no peroxo-group in this ion. So, for the most common ions, it is best to simply learn these things. For the more special things, the IUPAC naming convention is used more and more, which is unambiguous, but unfortunately also somewhat awkward. http://www.iupac.org/reports/provisional/abstract04/connelly_310804.html
  17. YT, really this is one of the best explanations I have seen . It perfectly explains the problem in a nutshell.
  18. Yes, that is possible. There are some basic rules: C-atoms have 4 bonds O-atoms have two bonds H-atoms always have 1 bond N-atoms have 3 bonds There may be double bonds between atoms. An example: C4H10O This can be CH3CH2CH2CH2OH CH3CH2CH2OCH3 CH3CH2OCH2CH3 (CH3)3COH CH3CH(OCH3)CH3 CH3CH2CH(OH)CH3 All isomers can be listed systematically. One has to be careful not to forget one, and one also easily mentions doubles. It is not always true that all isomers, which can be constructed, using the enumeration of all possible arrangements, also exist in reality. Some structures require spatial arrangements of atoms, such that atoms would overlap in space. Of course, that is not possible and such isomers do not exist in reality. Altogether, given just a formula, in general, it is not easy at all to determine all possible isomers, which also could exist in real life.
  19. Popularity of science on a whole is diminishing. A lot of people talk about science (and pretend they know quite a lot of it, and draw far reaching conclusions from it), but only few people really do science. This is true in society in general, and it is true for SFN also.
  20. Official chemical suppliers like Aldrich, Alfa-Aesar, etc. do not sell to individuals. They only sell to companies with registered lab-facilities and to universities, schools, etc.
  21. I have done a PhD on mechatronics and control theory. Lots of mechanics, mechanical engineering, electronics and especially mathematics. I switched career after that. Now I'm working in IT as software engineer. Chemistry/experimenting is a hobby for me.
  22. OK, now the question is clear. I'm not an organic chemistry expert, but just by looking at the reactants and looking at the solvent and trace KNH2 I think that the KNH2 plays a catalytic role. The main net reaction most likely will be: (C6H5)3C-K+ + C6H5Cl --> C(C6H5)4 + KCl. The mechanism for this could be: C6H5Cl + NH2(-) ---> C6H5NH2 + Cl(-) Nitrogen is most electronegative and the charge may shift to the nitrogen atom, resulting in something like the following: (C6H5)3C(-) + C6H5NH2 <---> (C6H5)3C.C6H5NH2(-) --> (C6H5)3C-C6H5 + NH2(-)
  23. woelen

    redox reaction

    You will end up with a precipitate, or with a brown clear solution, depending on how much KI is used (assuming that there is more than sufficient acid added). Andie, please think about this yourself and show that you have put some effort in the problem. This is not http://www.spoonfeeding.net . There are many knowledgeable people over here, and they are willing to help you, but we may also expect some input from you.
  24. woelen

    pl help

    Jdurg's way of reasoning is perfectly valid. For electron-gaining, the element fluorine is most reactive and going downwards along the halogens, the reactivity decreases. This can be explained, due to increasing radius of the atoms. For the alkalimetals it is the other way around, but now electrons are given up. Cesium is large and the electron can more easily be given up, than by any other element and when going upwards, the giving up of the electron becomes less facile and hence the metal becomes less reactive.
  25. Feel free to share some problems in the field of chemistry over here. Enough problems are addressed here, and if you want to participate in those discussions, of course, you also are welcome to join them.
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