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teenwitch24
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[*] posted on 9-2-2006 at 15:43
Chemistry project


Hello!
I am a student with a chemistry project. My teacher gave me an equation that I must name. I must also find a way to make the reaction go faster. Here it is:

2Al+ 3 H2SO4? Al2 (SO4)3 + 3H2

Thanks!

Katherine
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guy
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[*] posted on 9-2-2006 at 15:48


It is a single displacement reaction because Al replaces the H+. Also it could be called a redox reaction because Al reduces H+ and Al is oxidized to Al+++. Increasing temperature by 10K usually doubles a reaction rate.



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darkflame89
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[*] posted on 10-2-2006 at 06:39


Conversely u can also add some copper(II) sulphate to speed up the reaction too.



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teenwitch24
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[*] posted on 10-2-2006 at 11:49


Thanks for your help, but what is it? I mean, the common name.
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treelike
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[*] posted on 10-2-2006 at 12:02


Aluminium doesn't really react with sulphuric acid if I remember correctly. I guess it's one of those reactions that work in theory but when you dump a piece of Al foil into a test tube of H2SO4 you'll see a whole lot of nothing going on.

I think the problem is that there is a film of oxide over the metal, which protects the metal from attack. If you rub some mercury over the aluminium first this removes the oxide and I guess you could say that this will speed up the reaction, although I suspect that the oxide or possibly a sulphate layer will build up rather quickly and slow down the reaction again.

Dump some Al into hydrochloric acid and that one is a bit more exciting, the AlCl3 produced catalyses the reaction and it gets quite violent with hydrogen and steam coming out of the test tube (unfortunately the steam/ corrosive HCl vapour prevents the hydrogen from being ignited)

Sorry I didn't really answer the questions just blabbering for interest's sake.
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neutrino
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[*] posted on 10-2-2006 at 14:06


No, you're thinking of nitric acid. Sulfuric acid attacks Al just fine.

The common name? Dissolving a metal in an acid? I'm not really sure what you're looking for here.
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12AX7
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[*] posted on 10-2-2006 at 18:05


Water might do it. I've distilled >92% H2SO4 + NH4NO3 (or something like that) with aluminum present in the mix and it didn't get much wear. Seems to me moisture caused rapid corrosion (foaming and heating of the mixture).

Like iron, concentrated sulfuric has no effect on aluminum.

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neutrino
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[*] posted on 10-2-2006 at 21:02


Really? I didn't know that. I thought that concentrated sulfuric acid's strong oxidizing properties only became significant at high temperatures, such as when dissolving silver.
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teenwitch24
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[*] posted on 12-2-2006 at 06:44


Thanks for your help, I just want to check if I got it right. A metal and an acid produce a gaz? Wich is hydrogen. To make the reaction go faster, I simply need to heat it up?
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sparkgap
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[*] posted on 12-2-2006 at 07:54


For reactions like that, yes. Heat has this nice tendency to increase the so-called "rate of reaction"... ;)

sparky (^_^)




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runlabrun
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[*] posted on 21-2-2006 at 19:54


in schools sometimes these reactions are generalised to be 'hydrogen producing reactions' seeing as the reaction of any metal and acid produces hydrogen. However doesnt NaOH and Al make hydrogen too?

As a teacher i see this going on all the time in schools, teachers who may not be fully qualified in chemistry rather being allowed to teach chemistry due to a few subjects or inservice training sessions they have attended (bad i know but it does happen) are usually the culprits. I personally dispise these common terms being used to describe such reactions as they are not appropriate chemical descriptors of exactly what is going on, hence the students get no real benefit except confusion.

So as for general terms i would say the teacher is asking for this... either metal/acid reaction or hydrogen producing reaction. As for speeding it up, increase catalyst - temp is an obvious one...

@darkflame89
how does CuSO4 spead up this reaction? wouldnt sulfate solubility in conc H2SO4 would be low due to common ion interferance?

-rlr
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[*] posted on 22-2-2006 at 00:54


CuSO4 does not speed up this reaction. A combination of CuSO4 and NaCl (or CuCl2 alone), however, tremendously speeds up the reaction. If only NaCl is added then again there is no speed up.

The combination of Cu(2+) ion, Cl(-) ion and acid is extremely powerful in dissolving Al-metal, MUCH more than acid alone. Try it and you'll be surprised.




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tom haggen
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[*] posted on 22-2-2006 at 00:55


Quote:

hence the students get no real benefit except confusion.


Am I to assume that confusion is considered a benefit?:P:P:P:P:P:P:P:P




N/A
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darkflame89
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[*] posted on 23-2-2006 at 01:29


CuSO4 would speed up the reaction, just very slightly. I did an experiment once in school, where we timed the rate of reaction of magnesium reacting with sulphuric acid. As a separate reaction, 2 drops of CuSO4 was added. The rate of reaction was higher after adding the CuSO4. This is because of a side reaction: Mg + Cu(2+)---->Mg(2+) + Cu. The formed copper metal on the magnesium then forms a electro-couple. This causes the magnesium to react with the acid much faster. This is very much like inserting an iron bar halfway in to an acid solution. At first, there are very little bubbles on it, i.e. rate of reaction is slow. Place another bar of copper metal into the acid and connect the iron bar to the copper bar by means of wire. Hydrogen will start to evolve at the copper bar at a much faster rate, and iron would rapidly dissolve in the acid.

Of course in this case, just copper sulphate is not enough to catalyse the reaction between aluminium and acid. This is due to the aluminium oxde layer on top of the aluminium which very much stops the reaction. Even copper sulphate does not react with passivated aluminium. As Woelen pointed out, using copper(II) chloride instead may have a greater result. The rate of reaction is so fast that in certain instances, the water may actually boil. (No joke, i tried it once, and accidentally touched the sides of the beaker. I ended up scalded.)




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