woelen

0/0 is undefined. One cannot say it is 0, a non-zero number or infinite. One can define limits of the form f(x)/g(x), with f and g going both to zero for a certain x, and then one can determine the value of such limits, but just a statement 0/0 equals XXX is nonsense, because nothing is specified over here. 0^0 can best be written as 1: take a limit of a^a, with a approaching zero from above, and you'll see that for non-zero, but very small a this goes to 1 arbitrarily close. For the rest, I think this issue is settled here and does not need further discussion.

I also have serious doubts on this one, but if bob000555 really has tried this and it really burns well, then of course we have an interesting thing. I can imagine that at sufficient high temperature CaCO3 decomposes to CaO and CO2 and that the CO2 supports combustion of Al. The heat of that reaction could decompose more CaCO3 and so the reaction can be sustained. It is a well known fact that magnesium burns brilliantly in an atmosphere of pure CO2, producing MgO, CO and C. In fact, you get lots of soot when burning Mg in an atmosphere of CO2. So, it is imaginable that the Al/CaCO3 mix works by formation of Al2O3 and C (and CO) from the Al and CO2. Let bob000555 comment on this and describe how he did the experiment.

I doubt whether MgO2 does exist. It might be a peroxide, but I wonder if you ever can get your hands on that (if it exists at all). Probably you mean MnO2. That indeed can make a good thermite. I mentioned it in my list of examples in the previous post. The reaction never goes circular. What you describe is going circular from Al + metal oxide to Al-oxide + metal and then vice versa. That does not happen. You only have one reaction and when one of the reactants is used up, then the reaction stops. This has nothing to do with heat being dissipated. Heat is not the driving force of the reaction (although it may help initiating the reaction). The driving force is the potential energy, stored in the reactants. Does CaCO3 / Al really burn well? How easy is it to ignite this mix?

Well, I must say that metals CAN have a smell. I don't know what causes the smell, but it definitely exists. Try rubbing a copper coin with your fingers and then smell your fingers. Do the same with iron objects. Also non-volatile salts of metals can have a smell. Dip your finger in a solution of FeSO4 and let it dry. Then smell your finger. Same smell as when you manipulate some iron objects. Also if you count money, then you'll certainly notice the smell on your hands after you have done that. For me, these metallic smells are not unpleasant, nor pleasant. They just are there. But I agree with YT, that dry metal salts and also the dry metals, are odorless. The smells I describe only appear when the metal or its salts are rubbed with your hands.

Either you have to define a new 'elementary' function, and in fact matt grime did with his 'F' function. This is a perfectly suitable way of reasoning, especially if a certain form of integration becomes very common and is needed many times in different fields of science. Or you have to resort to numerical methods, which can provide you the value of the integral for any starting point and end point within the validity area of the function sqrt(sin(x)). If you want an answer in terms of high school standard functions like sqrt(), sin(), cos() etc, then you will probably be disappointed. There is no such answer. Many integrals cannot be expressed in terms of the elementary functions, but this does not mean that they cannot be integrated, so your teacher's answer is not (fully) correct. What he means is that the integral cannot be expressed in terms of standard high school functions. A nice example of extending the set of standard functions is when it comes to integration of functions of the type C*exp(-D*x*x). It is not possible to write integrals of this type of functions in terms of e-powers, sines, cosines, etc. This type of integrals, however, is very common in statistics, but also in certain parts of physiscs. For this reason a new 'standard' function is introduced, the so-called error function, erf(x). With the definition of this function at hand, one now can express integrals of the form exp(Ax²+Bx+C) in terms of the (complex) erf() function, and possibly other highschool standard functions as exp(x).

So, you have a perpetuum mobile???? Bob000555, please think twice before you post. This is nonsense. MgO and Al make no good thermite. Lime plus aluminium also is crap thermite. Did you ever try it yourself??? For a thermite reaction you need a free very electropositive metal, mixed with the oxide (or halogenide) of a much lesser electropositive metal. Some examples: Al and Fe2O3 Al and CuO Al and Cr2O3 Mg and V2O5 Mg and MnO2 Al and CuCl2 Mg and Ag2O Also, the metals and the oxides must be very finely powdered. If you ever try these reactions, also keep in mind that some oxides and chlorides are volatile (e.g CuCl2, to some extent V2O5).

I would simply use the white material and discontinue the use of the grey stuff. The grey material may be aluminium in the form of fine filings or granules. That frequently is added to drain cleaner to make it more powerful, when used in hot water. Sodium hydroxide (the white material) reacts viogorously with aluminium (the grey stuff), when mixed with hot water. This violent reaction, which produces a lot of bubbles (of hydrogen gas) helps unclogging the drain. I would NOT sell the soap you made with the grey material. Although aluminium is not that toxic, repeated exposure and especially intake of small amounts of aluminium may promote development of Alzheimer's disease. There is no big chance that such a thing could happen, but you definitely do not want all the liability issues associated with that. So, lesson learned: If you use NaOH for soap making purposes, assure that the material is pure white, otherwise it is not good.

Unfortunately it is not easy at all to give a single balanced equation for this reaction. In fact, this reaction is increadibly complex to understand. I have asked a few experts already about this, but it apparently is not fully understood why this reaction occurs so rapidly. It will be a combination of redox reaction, complex formation and physical processes at the Al-Al2O3 interface. A very coarse approximation of what happens is the following: 2Al + 6HCl --> 2Al(3+) + 3H2 + 6 Cl(-) The following occurs: 3Cu(2+) + 2Al --> 3Cu + 2Al(3+) But in reality, there are many complicated intermediates. The reaction probably proceeds over complexes like H2CuCl4 HCuCl4(-) and CuCl4(2-). Also chloro-complexes of aluminium will be evolved. The reaction equations above are just net reactions, the upper one being the main reaction, but as a side reaction, also some copper metal is formed. No, first I want to say that no NaAlO2 and AlCl3 are formed as solids. You get hydrated ions in water, such as AlO2(-). AlO2(-) and Al(3+) cannot exist in water at the same time, this will result in formation of Al(OH)3 precipitate, or, in the presence of chloride, some mixed hydroxo-chloro-precipitate of aluminium. Anyways, the colors of all these compounds are either colorless (in solution) or white (as solid/precipitate). Any murky, black, or whatever other color, is due to impurities of other metals.

No, it won't cut up your lungs. It was a one-time exposure, and it is no worse than breathing any general dust for a single time. So, no need to worry. Of course, if this happens many times, then it will be harmful, even maybe just of all the dust, but again, for a single time there is no need to worry. Shock cooling of a liquid molten compound is not the best way to make crystals. By shock cooling you tend to obtain amorphous compounds, or polycrystalline compounds, consisting of very small irregularly ordered crystals. Making good large uniform crystals requires very slow cooling.

Fortunately bismuth is non-toxic, even in quite large quantities. So, no need to worry. Next time, please think twice before you do something like this. If this were lead, then you could have been screwed! Bismuth is quite remarkable in the sense that it non-toxic, while all surrounding elements in the periodic table are toxic, very toxic, or extremely toxic. This is a good thing of bismuth and makes experimenting with bismuth relatively safe. Btw, what was the purpose/goal of your experiment?

This is a well known effect of sodium bicarbonate. Where I live it is called "zuiveringszout" for this reason, which can be translated as "purification salt". It removes smells. I have heard the explanation that it does so, by formation of CO2, which replaces the smelly molecules in the structure of the object to be "purified". The CO2 expells the smelly stuff and replaces it. This explanation sounds reasonable to me, but a nice experiment would be if someone with access to pure CO2 (e.g. CO2-"ice") could do a test. Put some of it in a smelly container and leave it there for a while. After that, the smell should have disappeared. If that experiment is confirmative, then that would be great evidence of this CO2 hypothesis.

Here catch is that -1 does not equal sqrt((-1)²). This is OK for positive numbers, e.g. 2 = sqrt(2²), but for negative numbers you cannot do this. The function sqrt(x) is defined to give a positive number for all positive x. You could introduce a new function sqrtn(x), which returns the negative value, e.g. sqrtn(4) = -2. But what is done in that "proof" above, is sometimes using the positive definition of the sqrt() function and sometimes using the negative definition of the sqrt() function. In the step from -sqrt(-1) to sqrt((-1)²*(-1)) the negative definition, equivalent to sqrtn() is used, while in the step from sqrt(1*(-1)) to sqrt(-1) the positive definition is used. EDIT: While I was typing, Severian was just before me Luckily we say the same.

This particular function indeed is quite complex, but the mechanism of solving it is not that difficult. First take the Z-transform of the equation, regarding x as discrete time: Y - aY/z = cz/(z-1)² + dz/(z-1) Y can be expressed as function of z: Y = c/((z-1)²(z-a)) + d/((z-1)(z-a)) This can be written as (c- d + dz)/((z-1)²(z-a)), which in turn can be written as P(z)/(z-1)² + Q(z)/(z-a). Here P and Q are polynomials in z. P is a quadratic polynomial in z, Q is first degree in z. So, in the Z-domain your solution Y(z) has only terms of the form C1/(z-1)², C2z/(z-1)² and C3z²/(z-1)² and terms of the form C4/(z-a) and C5z/(z-a). Here, the C's are all constant (of course, different for each term). Now you need to transform back to the time domain. The value z/(z-1)² has backtransform x. Then of course, the values multiplied with powers of z are simple. These simply are shifted versions of x in time. E.g. 1/(z-1)² has backtransform x, but at time x - 1. This simply is x - 1, and similarly z²/(z-1)² has backtransform x + 1. The term z/(z-a) has backtransform a^x. Again, 1/(z-a) then has the same backtransform, one timestep shifted, that is a^(x-1). Now it is just plain algebra, collecting all the terms. That exercise I leave to you .

I like the idea of Mooeypoo very much, and that is why I have set up a fairly large site already about experiments and all practical things which are involved with it (such as safety, obtaining the needed materials). A project like ExperiWiki would be really great, but I have to admit that Atheist has a very important point. Such a project easily dies after the initial enthousiastic start. The amount of work is very large and people really need to be persistent on that. Just to give you an impression about my own website: Initial idea: Dec. 2004 Setup of main format, layout: Jan 2005. Doing experiments, making pictures, writing descriptions: Feb. 2005 - Jun 2005. Initial launch of website: Jun. 2005 At the initial launch there were appr. 10 experiments with pictures, there was info on most elements, the site already had a fairly finished look. So, I have been busy HALF A YEAR before I first put it on the Internet. I am a real passionate, so I spent that time with great pleasure, but I can imagine that many people are not that passionate, and then things become difficult. Such a site MUST have a fair amount of content, before it is published. An empty shell does not work, is not inviting and only is disappointing. My site was fairly complete when it started, and the effect of that was that I had more than 1000 hits per day, only a month after its release. Now, one year later, the number of hits still is around 1000 per day and new experiments are added every now and then (now I want to emphasize more on physics, which now still is blocked, but when accessible it will have a fairly complete section, just as the chemistry section one year ago). So, if an initiative like ExperiWiki is started, then think twice about the initial startup. But I want to tell you, Mooeypoo, that if such an initiative is started, you get my blessings, and more than that . I'm willing to supply materials for that site (e.g. pictures of elements, experiments, etc.). I, however, have no time to really work on the layout and actual publishing, because I need that time for my own website.

Indeed, I've heard of more people from Australia that their rules on chemicals indeed are insanely strict. Over here, where I live, chemicals are not that easy to find, but only few chemicals are illegal for purchase. In fact, compounds like K2Cr2O7, KMnO4, Na2S2O8 can be purchased in many shops like electronics stores, ceramics/pottery suppliers and the well-equipped online photography shops.

Could you provide us with an example of a difference equation which needs to be solved? Indeed, the methodology for solving linear difference equations is somewhat similar to the methodology for solving linear differential equations. Main difference is the stability criterion, which for linear differential equations is that the real part of the eigenvalues must be less than 0, for the difference equations the absolute value of the eigenvalues must be less than 1. Also, the solutions for homogeneous differential equations are exponentials of the eigenvalues, while for difference equations you get powers of the eigenvalues.

Marjorie is talking about calcium sulfate, not copper sulfate. Magnesium sulfate is water soluble, yes it indeed is very water soluble. Double decomposing CaSO4 into a more soluble calcium salt and a more soluble sulfate is VERY hard. I see no practical way to achieve that, because CaSO4 itself is highly insoluble already. With a LOT of patience you MIGHT be able to dissolve CaSO4 in a solution of Na2-EDTA, forming the very strong soluble calcium-EDTA complex and Na2SO4 in solution, but this is a very cumbersome way, and I do not guarantee that it really works. It just comes into my mind.

You can also make acetone out of it by oxidizing it with any oxidizer, such as KMnO4, K2Cr2O7, Na2S2O8, etc. This reaction is slow and requires some heating, but it works. You can smell the acetone easily. It is, however, not interesting as a preparative route for acetone, it is just interesting as a curiousity.

I think that carbon (graphite, and diamond) has the highest boiling point. In fact, it sublimes. IIRC, this happens at temperatures between 5000 and 6000 C. Maybe it is not the compound with the highest boiling point, but it certainly is among the compounds with the highest boiling point. Of course, all this must be specified at atmospheric pressure. At much higher pressure, such as in the core of the planet Jupiter, even hydrogen can exist in solid or liquid state, while white-hot, with metal-like properties. But that is at a pressure of millions of earth's atmospheres.

I'm not sure whether tin is magnetic or not (but let's suppose that is true), but when a metal is magnetic, then surely its compounds (e.g. oxide) need not be magnetic. Being magnetic is a property of a compound, just like color is a property of a compound. When a new chemical compound is formed, then the properties become totally different. There also is a second misconception in bob's post. An alloy cannot be separated by grinding. E.g. when I have an alloy of iron with another non-magnetic metal, then one cannot grind it so fine, that the non-magnetic metal and the iron can be separated by magnets. Even the tiniest particles still have the iron and the other metal intimitely mixed (at the atomic level). One would have to break down the metal to the atomic level, but that implies making a new compound.

Rocket man, I did the experiment with a plasma cathode. The effect is quite similar to the situation with a plasma anode, but all effects are much weaker. The color of the plasma beam also is different, it is more red/purple, while the anode beam is more blue/purple. Most noticeable, however, is that things are weaker. YT, I also did an experiment, by putting a piece of Al-foil under the petri dish, and connecting this foil to the cathode. The effect of this is quite stunning. The electrolysis now is extremely noisy. In fact, I do not get a nice steady beam anymore, but sparks at a very high repetition rate (a few 1000's of times per second I estimate). The Al-foil acts as cap of a few tens of pF, and this is charged and discharged by means of a real spark. There is no plasma anymore, but sparks jumping around in all direction from the cathode. More spectacular, but also less controllable. At times, I also had severe arc-over over the rim of the petri dish from the liquid, around the glass, into the Al-foil underneath the petri dish. The setup had to be adjusted carefully and the petri dish had to be cleaned carefully in order to prevent arc over.

Citric acid is a fascinating chemical, when combined with transition metals. It forms nicely colored complexes with most transition metals, especially, when the pH is brought to a value higher than 7. The most remarkable complexes are formed with vanadium in its +4 oxidation state (easy to make from V2O5, which is a common chemical), and with copper in its +2 oxidation state and iron in its +3 oxidation state. With iron in its +3 oxidation state, you can make a nice light sensitive chemical. Do a google with "cyanotype". This is a very neat experiment, which only requires an iron (III) salt, some citric acid and red prussiate of potash (potassium ferricyanide).

The following webpage describes an experiment I did with electrolysis of a solution of NaCl and KI with a copper wire as cathode, and a little plasma beam as anode. This is a very special experiment, which I want to share with you. If you want to repeat this experiment, be VERY careful. It is a dangerous experiment, and should only be performed if you really feel confident that you safely can do this. I also had a small accident, which was quite painful (droplets of water and salt hitting the skin at very high speed). The experiment can be seen here: http://woelen.scheikunde.net/science/chem/exps/HV_electrolysis/index.html No need to fear that k3wls will do this experiment, because the required apparatus is not in the average k3wl-house . The AVI files in the webpage usually can be opened by simply clicking them, but with some versions of Windows, you first need to download them to your harddisk, before the playback works. So, if it does not work, please download them to your local disk and then try again.

I did some experiments with the metal iridium. I have some iridium salt and did some experiments with that, which I want to share over here. This metal indeed is worth its name. With only very simple chemicals you can reach all colors of the rainbow, really neat. Have a look at the following web page. http://woelen.scheikunde.net/science/chem/exps/iridium/index.html