catalyst reactions

[darklar]

I want some big experiments to photograph that are based on showing catalyst effect. I'm not too hot at science and wondered if anyone knew some examples of a catalyst in action I could use...

or just some catalysts... not necessarily chemicals. ie salt and ice.

thanks for your brains.

[jake-the-peg]

One of the best examples is the Ozone hole.

That's why Chlorine compounds such as carbon tetracyclene are so damaging , one molecule of CCl4 does not kill just one ozone molecule but hundreds or thousands

have a look here

http://www.atm.ch.cam.ac.uk/tour/part3.html

[darklar]

thanks for that Jake... I was hoping to be able to photograph the reactions as they happened though.

[jake-the-peg]

That's a bit of a toughie.

A catalytic reaction looks like any other chemical reaction it's just that one of the elements helps the reaction takes place but is not in itself used up.

Here's a couple of pictures of a catalytic combustor but it's just a glowing tube - any use?

http://www.me.berkeley.edu/cal/CATALYTIC/index.html

[shammydodger]

Jake

Isn't the reaction that destroys ozone a chain reaction and thus the (e.g.) carbon tetrachloride (sic) an initiator rather than a catalyst?

As for a suggestion, darklar, one of the first catalysed reactions I was familiar with at school was the catalytic decomposition of hydrogen peroxide, with manganese dioxide as the catalyst. It wasn't what one could call spectacular, though one could witness the effervescence as the reaction proceeded. You might wish to google it to see if it is available as a video link.

[shammydodger]

Actually, I've just googled it myself and it's a bit livelier than my memory gave it credit for. Here it is:

http://www.cci.ethz.ch/experiments/katal_H2O2/en/stat.html

[jake-the-peg]

Light breaks cloroflorocarbons etc down to release chlorine

CF3Cl + hn CF3 + Cl

The ozone then reacts with the Chlorine so:

Cl + O3 → ClO + O2
ClO + O → Cl + O2

So actually stricly speaking it's the chlorine that's the catalyst but it is a catalytic reaction

Well done on the pictures

[shammydodger]

Well, Jake, we are just going to have to agree to disagree. The propagation steps you show do indeed suggest that that part of the chain reaction is a catalytic process, since the Cl radical is regenerated. However, the chain reaction as a whole is not a catalytic process because the initiator is not necessarily reformed. There are many possible termination steps and thus byproducts, so if one started out with, say, 1g of a particular initiator, you would not get back 1g of that initiator when the reaction finally ceased. Thus, by definition, it cannot be a catalytic reaction.

But thanks for the comment on the video!

[shammydodger]

Darklar

Another reaction that comes to mind is the oxidation of iron to iron(III) oxide, with sodium chloride (common salt) as a catalyst. Here is a brief description:

Put iron powder in a plastic bag, e.g. a "Ziploc" bag. Add sodium chloride and mix contents by shaking the closed bag. Add 1 tablespoon of small vermiculite pieces and mix again. Add 5 mL water to the bag and seal with a twist tie. Squeeze and shake the bag. After 2 minutes feel the bag and observe the heat produced. The iron powder and the oxygen in the bag react to form iron oxide. Salt speeds this reaction and is therefore a catalyst. The vermiculite insulation ensures that the heat stays in the bag. The iron oxide formed is a compound.
2Fe + 3O2 ---> Fe2O3 + heat

I wouldn't know if this is worth filming. However, there will be a colour change of the grey iron powder to the reddish iron(III) oxide. How noticeable it would be amongst the other "ingredients" I wouldn't know without performing the experiment myself, and I'm fresh out of vermiculite!

[jake-the-peg]

Interesting Shammy, I see where you're coming from.

I suppose really you could say that there's a catalytic ozone depleting branch within a complex sequence of reactions

I guess it's just as well for us and especially the Southern Hemisphere that there are termination steps otherwise we'd have no ozone layer at all.

Still mustn't hijack the thread

[shammydodger]

Darklar

Then, of course, there is the yeast-catalysed fermentation of sugar to alcohol. This is an example of a biological catalyst (enzyme) in action. Mind you, you'd need to be well-versed in the technique of time-lapse photography as it's not a reaction that happens in minutes. Maybe you could do a "before-and-after" study. A pint of sugary water with a bit of yeast chucked in (click), then a shuffle down to the local hostelry (what an excuse) to become acquainted with a pint of ale (click)! Just a thought :)