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Everything posted by woelen

  1. woelen

    Absolute Zero

    The equations for the gas law are macroscopic equations, which are based on statistics. At temperatures near 0 K these approximations do not apply anymore, the equations only are good approximations of reality over a certain interval of temperatures.
  2. Not exactly. Dissolve in less than 100 ml of water, and then add water while stirring, such that the total volume is 100 ml. With this 0.01 M solution Darkblade's method will only introduce a marginal error, but with more concentrated solutions the error may become considerable.
  3. The material from batteries (only zinc/carbon batteries are OK) is VERY impure. It is mixed with carbon and possibly other crap. Besides that, it is extremely messy and dirty. A much better source are the ceramics and potteries suppliers. These sell MnO2 at reasonable (certainly not reagent grade) purity, suitable for most home experiments.
  4. Please no cross posting. One post is enough! Further discussion is here: http://www.scienceforums.net/forum/showthread.php?t=24967 THREAD CLOSED
  5. Are the concentrations of the solutions the same? Also, in copper sulfate the ions have two units of charge, which makes discharging the ions slower. The ions in copper sulfate (esp. the sulfate ion) also are larger, which makes them less mobile.
  6. I think you only obtain ClO2. The active ingredients are KClO3 and H2SO4. Probably you get the same result without the Cu(NO3)2.xH2O.
  7. Time and space are really different things, but there is a relation between them (general relativity, but even special relativity). We perceive 3 spatial dimensions and a single time dimension. Now imagine a 1D spatial world. It would be quite dull, because we could only move along a line, but we could move forward and backward. We still could perceive time in such a world. So, actually, such a world is a 2D world, with one spatial dimension and one time-dimension. A truly 1D world would either be a single point with time, or a line/curve, without time. I myself look at it as follows: We are moving at a constant speed through space-time, where temporal motion is at 1 second per second when we are not moving in spatial direction. When we are moving in spatial direction, then the motion in temporal direction becomes slower, but the total 'speed' remains the same. The quantity [math]c^2t^2 + v_x^2 + v_y^2 + v_z^2[/math] (which is my 'speed trough space-time' remains constant at [math]c^2[/math]. So, if one of the v's is going to c, then t must go to zero. I must admit, that this is quite a sloppy explanation (in reality, one cannot speak of an absolute velocity, it is relative to something) and the math behind this is MUCH more involved, I post this to give just an idea of how you can look at it. If you move faster, then less remains for the speed at which time elapses for you.
  8. woelen

    SFN logo

    Oh?? Is it winter? This year we had summer till November and now we have autumn with lots of wind and rain, which soon will smoothly turn into spring again.
  9. The results of your experiments do not surprise me. Although metals in theory should yield H2 on dissolving in acid, in practice those reactions can be VERY slow. Nickel hardly will react. Even in concentrated hydrochloric acid it does not react quickly, although it does dissolve. Iron reactivity can be greatly reduced by adding small amounts of other metals (e.g. chromium, vanadium, nickel). Stainless steel is an example of that. I have done experiments like this with many metals, and also in many acids, and only a few metals are really reactive.
  10. Best results are obtained with a titanium anode, covered with a non-permeable coating of ruthenium dioxide. Second best are platinum anodes, but these are corrodes quite badly already. Both types of anodes are not something the average person has lying around. They are VERY expensive, but if you wish, every now and then, suitable materials are offered on eBay and for $100 or so you could make your own anode.
  11. I already read the message on sciencemadness, and I've been thinking about that for some time, and now I think it is volumetric glassware for volatile liquids (the long neck assures that there is not much loss of liquid, due to evaporation). Such glassware allows you to measure volumes with very good precision, but you only have a few readouts. I myself also have one such bulb, but without the long neck. I use it for measuring 20 ml of liquid at high precision.
  12. Cap'n, what you say is only true for neutral covalent compounds. However, ions can also be covalent. Let's look at the well-known compound KNO3. This is an ionic compound, consisting of K(+) ions and NO3(-) ions in a 1 : 1 ratio. Inside the NO3(-) ion, however, we only have covalent bonds. You can look at the ion NO3(-) as a covalent "molecule", which happens to have a single charge.
  13. I also would say, this is 2.8, but the margin can be less than 0.2, I would say 2.8 +/- 0.05.
  14. The 9V batteries are useless for this. You need a BIG battery, with good electrodes. Use a lantern battery, 6 V, type 4R25. Be careful to select a zinc/carbon type. This type of batteries has 4 beautiful large rods in it. It is quite a mess, however, to remove them, but it is worth the effort. These batteries also are cheap, around $5, so the price of the rods will be just $1 to $1.50 each. Batteries like this can be purchased in hardware stores, they are not present in the average supermarket or photography shop.
  15. In fact, it is not really true that NaOH is formed. We are talking about ionic compounds, and it is better to say that hydroxide is formed. At the cathode, electrons are 'pushed' into the liquid, and this causes water molecules to be broken down as follows: 2H2O + 2e --> H2 + 2OH(-) You see? The source of the hydroxide is the water. The sodium ions just do nothing, and this is because electrons can easier be passed to water molecules than to sodium ions. If you were working with molten salt, then there is no water, and then the electrons are passed to sodium ions: Na(+) + e --> Na In molten salt, sodium ions accept electrons easiest. Chloride ions cannot accept another electron. In general, when electrolysing things, electrons are given off at the cathode and are consumed at the anode. Both at the cathode and the anode, you have to look at what is present over there and what of all those different things can easiest accept (or give away) electrons. You have to consider 1) The solvent (if any) 2) The ions 3) The electrode material itself In the case of electrolysis of NaCl in water with copper electrodes, you have available near the cathode: Cu metal Na(+) ions Cl(-) ions water Of these 4 things, water can accept electrons easiest. At the anode, when using a copper anode, the same four things are present. Now the question is, which compound can easiest give off electrons (the anode absorbs electrons). Now this is the copper metal. So, the copper anode will dissolve and erode. Now suppose we are electrolysing molten sodium hydroxide with copper cathode and platinum anode. At the cathode we have: Na(+) OH(-) Cu metal Of these, the Na(+) ions easiest accept electrons. So, sodium metal is formed. At the anode we have Na(+) OH(-) Pt Of these, OH(-) easiest gives off electrons, forming OH. This quickly reacts, giving water and oxygen. So, at the anode you will see oxygen bubbling and also water bubbling (due to the high temperature).
  16. YT, as long as some technical properties about these compounds are discussed I see no problem with this. Things become different if syntheses and/or trading of these compounds are discussed.
  17. Theoretically I have to agree with John. Even distilled water conducts some current (it self ionizes a little to hydrated OH(-) and hydrated H(+), the product of the concentration of these ions being 10^(-14) mol2/l2 under standard conditions). Practically, however, that conductivity is very low and with voltages of 9 V, IIRC the current will be in the order of microamperes.
  18. Selenous acid is H2SeO3. What is the ion, derived from this acid? When this acid is broken down, it is converted to selenium (this is a notorious thing, solutions of selenites or selenous acid very easily become red, due to formation of selenium). You need a reductor for this. Show some of your own efforts with the info I have given and then I'm quite sure you will obtain further help.
  19. It can be made (with difficulty) by electrolysing a solution of a chlorate (free of chloride), with suitable really inert anode. But this process is not easy. Making KClO4 at home is not easy and requires quite some experience.
  20. John, you forget one important thing. H2 is formed at the cathode. For the rest, I agree. Chlorate also can be formed due to disproportionation of hypochlorite. It is the usual mode of operation of a chlorate cell.
  21. LOL I personally, however think that things are not that bad. Perchlorate/reductor mixes actually are quite "stable" and they need a considerable source of heat to be ignited.
  22. YT, in general this is true, but there are examples, where lower frequency input gives higher frequency output. An example of the formation of singlet oxygen and the fallback to normal oxygen. Each molecule has energy for light at wavelengths of appr. 1200 nm. What happens, however, is that two molecules combine and that a single photon of 600 nm is ejected and then both molecules fall back to their normal state. I have read even about a compound, which absorbs red light and emits green light. The compound then absorbs two photons and then it emits a single photon of higher frequency (more energy).
  23. You also need a good set of electrodes. The anode must be a graphite rod. Metal wires dissolve and are corroded very quickly. The power supply must be a decent power supply, capable of delivering several amperes of current. A small 9V battery is totally useless. The voltage to be used should not be too high, unless you use a set of resistors to limit the current. A very good method is using a modified PC power supply, with a set of resistors for current limiting. http://woelen.scheikunde.net/science/chem/misc/psu.html
  24. I would pass the gas through anhydrous CaCl2. It will not react with that. There are better drying agents, but these are either alkaline, or too strongly oxidizing. You could also give it a try with P4O10, which is very good, but also more expensive and harder to obtain. But I guess, that if you have access to H2Se, that you also will have access to P4O10. Do not use Mg(ClO4)2 or concentrated H2SO4. These certainly are too oxidizing and may lead to destruction of the H2Se.
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