combustion reactions

[akcapr]

For school i have to demo 2 decomposition reactions that look "cool". Since these ppl are newbie chemists they will only be impressed with stuff such as H2O2 with soap decomposing and NI3. ANy other ideas?'

 

Edit: dumb me- i accidentally called the tittle combustion reactions

[aommaster]

Ahh... a reaction looking cool.

 

Depending on what apparatus you have, I can think of 3:

1.Decomposition of zinc carrbonate by simple heating. The zinc carbonate changes colour to yellow when heated, and then goes to an off-white colour

 

2.Iodine trichloride (you must have good lab eq. for this). You have to use iodine chloride, a brown liquid. When you pass a sufficient amount of chlrine gas over it, it changes to yellow crystals. Looks cool, but extremely dangerous.

 

3.Simple decomposition of calcium carbonate. Decompose it, add water etc. The whole cycle!

 

Hope this helps!

[akcapr]

ya it has to look cool tho

[vrus]

Magnesium with steam ? I liked that one...

 

How bout some grp.I with water... or maybe acid

[woelen]

 

2.Iodine trichloride (you must have good lab eq. for this). You have to use iodine chloride' date=' a brown liquid. When you pass a sufficient amount of chlrine gas over it, it changes to yellow crystals. Looks cool, but extremely dangerous.[/quote']

I have done this experiment at home. It is not that dangerous, if you assure that you do not breathe any of the vapors. A description with pictures is here:

 

http://woelen.scheikunde.net/science/chem/exps/Cl+I/index.html

 

Another very neat experiment is zinc-plating of a copper coin. I also have done that experiment:

 

http://woelen.scheikunde.net/science/chem/exps/copper+zinc/index.html

 

The experimental description calls for a zinc salt. If you don't have a zinc salt, then you can simply add zinc to a solution of sodium hydroxide and boil for a while, before the experiment is started. In this way you make your own zinc-solution and with that solution you start off.

 

If you attempt to do one of these experiments, please follow the safety guidelines, given on the webpages!

[aommaster]

I have done this experiment at home. It is not that dangerous' date=' if you assure that you do not breathe any of the vapors. A description with pictures is here:

 

http://woelen.scheikunde.net/science/chem/exps/Cl+I/index.html

[/quote']

 

Yeah, I totally agree with you, caution has to be taken. The problem with this is that he will be doing it as a demonstration for a school event. And you know how school kids are

[RyanJ]

Yeah, I totally agree with you, caution has to be taken. The problem with this is that he will be doing it as a demonstration for a school event. And you know[/i'] how school kids are

 

Yup... don't we all. Worst thing about being 6th form (Staying in school for further education) is your often asked to help out in experiment lessons. I have heared of people stealing a small vile of Bromine and then they broke it in the school leading to the whole area having to be cleaned and some guy stealing some magnesium ribbon and stashing it down his trowssers. Needless to say it reacted with the seat and caused some nasty burns and he still denied trying to steal the thing

 

Anyway I'd say if you do with within a fume cupboard you should be fine

 

Just don't et the kids get their ands on the stuff (I even say some kid try to eat a Barium salt... lucky the teacher cought the idiot...)

 

Cheers,

 

Ryan Jones

[jdurg]

The most impressive one I know of is concentrated sulfuric acid and table suger. Mix the two and the sugar decomposes into steam and carbon. It's a VERY impressive demo and is easily done with standard chemicals.

[aj47]

Yeah, I totally agree with you, caution has to be taken. The problem with this is that he will be doing it as a demonstration for a school event. And you know[/i'] how school kids are

 

In my old school there were plenty of idiots and one of them managed to steal a clump of potassium after a demonstration and put it on his pocket which resulted with a hole being burnt into his thigh. Personally I think he deserved it

[aommaster]

Yeah, which is why I gave to 'safe' experiments.

 

How did me manage to steal the potassium? With gloves?

[YT2095]

1.Decomposition of zinc carrbonate by simple heating. The zinc carbonate changes colour to yellow when heated' date=' and then goes to an off-white colour

[/quote']

 

another nice one like that is Cobalt Chloride, it`ll go from dark blue to bright pink with temp change, It looks even more impressive if you dissolve it in alcohol, put it in a test tube with a stopper. the color change from taking it out of the fridge or into a glass of hot water from room temp is quite dramatic.

Sodium Sulphide soln also changes color on heating, from a light yellow to a deep red/brown.

there are others, but these are probably the most simple examples anyone could do

[woelen]

another nice one like that is Cobalt Chloride' date=' it`ll go from dark blue to bright pink with temp change, It looks even more impressive if you dissolve it in alcohol, put it in a test tube with a stopper. the color change from taking it out of the fridge or into a glass of hot water from room temp is quite dramatic.

Sodium Sulphide soln also changes color on heating, from a light yellow to a deep red/brown.

there are others, but these are probably the most simple examples anyone could do [/quote']

I tried both of these. The cobalt chloride indeed is very nice. Dissolve some cobalt chloride or cobalt sulfate or cobalt carbonate in 10% HCl (not more concentrated). The solution becomes pink. Heat the solution until it almost starts boiling. The solution becomes really beautiful deep blue. When it cools down again it becomes pink.

 

I also did the experiment with a solution of sodium sulfide (Na2S) in water. I'm afraid that with this one YT is mistaken. The solution is colorless and it remains colorless, regardless of how long it is heated, boiled or whatever. The only result I get is that it starts stinking a lot of H2S, when the sulfide solution is boiled for a longer time.

After somewhat longer exposure to air, the liquid becomes very light yellow, but this change is not reversible. This can be explained easily. Sulfide ion is oxidized to sulphur, which in turn reacts with excess sulfide to form yellow polysulfide ions.

[YT2095]

Hmmm... Very Odd indeed, I urge you try again with the sodium sulphide soln, you`ll need to get about 10 ml of water in a test tube, and add NaOH prills to this (2 spatulas worth) the soln will heat up so be carefull!

then add sulpher powder to this and warm it up gently, keep adding sulpher until no more will dissolve.

your soln will now be red/yellow and Not Clear.

 

you`ll find I`m far from Mistaken

[woelen]

Hmmm... Very Odd indeed' date=' I urge you try again with the sodium sulphide soln, you`ll need to get about 10 ml of water in a test tube, and add NaOH prills to this (2 spatulas worth) the soln will heat up so be carefull!

then add sulpher powder to this and warm it up gently, keep adding sulpher until no more will dissolve.

your soln will now be red/yellow and Not Clear.

 

you`ll find I`m far from Mistaken [/quote']

Ah... I see. You don't use sodium sulfide, but NaOH/S. From that you don't get sodium sulfide, but a very complex mix of sodium sulfide, polysulfides and thiosulfate (and as a side reaction you also get sulfite and polythionates). The polysulfides are strongly colored and these indeed deepen in color, when they become hot. But your experiment is quite different from mine. I took pure Na2S, which is colorless in solution.

 

What you get is the following:

Sulphur disproportionates as follows in NaOH-solution:

 

4S + 6OH(-) ----> 2S(2-) + S2O3(2-) + 3H2O

 

The sulfide ions form polysulfides, which are yellow to red/brown, depending on temperature and number of sulphur atoms in the anion:

 

S + S(2-) ---> S2(2-)

2S + S(2-) ---> S3(2-)

...

4S + S(2-) ---> S5(2-)

[YT2095]

"9. Physical & Chemical Properties

 

Yellow or brick-red lumps or flakes or deliquescent crystals; odour of rotten eggs."

 

taken from: http://www.proteachemicalscape.co.za/msds/msds572.html

 

that`s why I find it odd when you say it`s colorless.

I`ve not found anywhere that says it`s colorless either?

 

the smell thing we have in common between our experiments though, probably the sort of thing best done in tiny amounts or in a fume cuboard I recon

[woelen]

"9. Physical & Chemical Properties

 

Yellow or brick-red lumps or flakes or deliquescent crystals; odour of rotten eggs."

 

taken from: http://www.proteachemicalscape.co.za/msds/msds572.html

 

that`s why I find it odd when you say it`s colorless.

I`ve not found anywhere that says it`s colorless either?

 

the smell thing we have in common between our experiments though' date=' probably the sort of thing best done in tiny amounts or in a fume cuboard I recon [/quote']

 

Yes, the solid is yellow, see this picture on my site:

 

http://woelen.scheikunde.net/science/chem/compounds/sodium_sulfide.html

 

If you dissolve this solid, then the solution becomes colorless. Sulfide ions are colorless in solution, but most solid sulfides are colored.

 

What you have in solution are polysulfide ions and these give your solution such a golden yellow color. I also once did the experiment of dissolving sulphur in a solution of sodium sulfide. Then you get the polysulfides also, but without the thiosulfate impurity.

[YT2095]

Interestingly enough, I found this also.

the color also seems to vary with water of Crystalisation too, here it even speaks of Pink! LOL

 

http://www.webelements.com/webelements/compounds/text/Na/Na2S1-1313822.html

 

but if you go through the others (in the bottom righthand side) with the .5H2O and the .9H2O the color changes again

 

it Does list a White too.

[woelen]

Interestingly enough' date=' I found this also.

the color also seems to vary with water of Crystalisation too, here it even speaks of Pink! LOL

 

http://www.webelements.com/webelements/compounds/text/Na/Na2S1-1313822.html

 

but if you go through the others (in the bottom righthand side) with the .5H2O and the .9H2O the color changes again

 

it Does list a White too.[/quote']

This is quite common in fact and there are many chemicals with colorless ions, which have colored solids. Some of them are even temperature dependent. Some examples of solids, which are colored and whose solutions are colorless:

 

lead iodide: bright yellow

mercury (II) iodide: deep orange/red

silver oxide: black (solution forms colorless silver hydroxide, which is slightly soluble)

sodium peroxide: orange/yellow

sodium sulfide, water deficient: yellow or reddish.

 

In fact, I have sodium sulfide from two different sources, the one on my website has approximate composition Na2S.3H2O, the other sample I have has an unknown amount of water, but it is not very high. This stuff is light brown/pink and its solutions again are colorless. It is not a nice bright pink color, more brownish. I'll consider making a photo of this and put this on my website as well in the same page as the yellow sodium sulfide.

 

Did I convince you now that the solution you had is not sulfide and that the temperature-dependent color is due to polysulfide?

[YT2095]

Did I convince you now that the solution you had is not sulfide and that the temperature-dependent color is due to polysulfide?

 

yes and no, I don`t Disbeleive you, but I`de like to know what the ppt is when Zinc Sulphate is added to this "polysulphide" soln first.

 

there is a Distinct almost insoluble ppt that`s White in color and acts as Zinc Sulphide does (appart from the Glow-in-the-dark bit).

 

if this soln is NOT Sodium Sulphide, what`s the PPT then?

[woelen]

yes and no' date=' I don`t Disbeleive you, but I`de like to know what the ppt is when Zinc Sulphate is added to this "polysulphide" soln first.

 

there is a Distinct almost insoluble ppt that`s White in color and acts as Zinc Sulphide does (appart from the Glow-in-the-dark bit).

 

if this soln is NOT Sodium Sulphide, what`s the PPT then?[/quote']

 

It most likely is zinc hydroxide. Sulphide hydrolyses to a large extent and for many metals you cannot prepare the sulfide in the wet way. E.g. if you add chromium salts, you get Cr(OH)3, with iron (III) you get iron hydroxide, with aluminium you get aluminium hydroxide and probably with zinc you get zinc hydroxide and what remains in solution is HS(-) and in your case with the polysulfide solution, you most likely also get some very finely divided sulphur in your precipitate, which however may redissolve forming higher polysulfides.

 

I write "probably", because for zinc I never tried myself. But, as zinc is amphoteric and sulfide is very basic and hardly is present as real S(2-) but as HS(-) and OH(-), I expect that zinc forms the hyroxide as well. With the other metals I mentioned, I know that their sulfides cannot be prepared in the wet way by mixing a soluble sulfide and a soluble salt of the metal.

[YT2095]

Hmmmm...

 

intruiging! it certainly begs for further experimentation (time permiting).

 

Appologies to the Original Poster for straying off topic a little, it`s largely my fault, but as the saying goes, you learn something new everyday, and this has certainly been interesting!

 

Thanks again Woelen, I`ve enjoyed this discussion this alot, and now have one or 2 more ideas to consider as a result

 

getting back to topic, if the OP wants to demonstrate this color change with heat experiment, follow the instructions as outlined a few posts ago with the NaOH soln and Sulpher, brick red <--> lemon yellow with heat <--> Cooling.

and it`s a Polysulphide reaction, not an ordinary single sulphide reaction

[jsatan]

another nice one like that is Cobalt Chloride' date=' it`ll go from dark blue to bright pink with temp change, It looks even more impressive if you dissolve it in alcohol, put it in a test tube with a stopper. the color change from taking it out of the fridge or into a glass of hot water from room temp is quite dramatic.

Sodium Sulphide soln also changes color on heating, from a light yellow to a deep red/brown.

there are others, but these are probably the most simple examples anyone could do [/quote']

lol.I did this with out know what I was doing when I was young,

I think I was about 11 or so, I just added water and put it on some paper, lol.

I'll have to try the ethanol.