Sciencemadness Discussion Board - Demonstrating platinum as a catalyst

Demonstrating platinum as a catalyst

craynerd - 10-10-2006 at 12:33

I need to demonstrate platinum as a catylist.

Basically, i heard a demo i could try but i don`t fully understand what it is showing or what the reaction is...maybe someone could fill me in.

Add a small volume of conc. ammonia to the bottom of a wide neck conical flask. Bubble through oxygen at a slow rate using a oxygen cylinder, tubing and glass tube to bubble it below the surface of the ammonia.
Take a platinum coil and heat it up in a bunsen until it glows. Remove it from the flame and place it some way into the conical flask (containing the oxygen which has been bubbled through the ammonia)

I have all the equipment.

Now as daft as this seems, i have explained the method but i don`t really understand what is going on. I ThInK when you place the platinum into the conical flask it ment to glow again, due to it acting as a catylist and increasing the rate of this exothermic?? reaction?

I am guessing...

Ammonia + Oxygen --> nitrogen mon/di oxide? + water

where the platinum acts as a catylist?

Basically, just hoping someone might be able to clarify what is exactly going on, or even give me a better demo to show platinum as a catalist?

cray.

EDIT: to save over embarrassment I have removed ammonia dioxide...what was i thinking :S

[Edited on 11-10-2006 by craynerd]

chemoleo - 10-10-2006 at 14:07

Funny this was the first reaction I was thinking off, oxidation of ammonia using a Pt catalyst.

ammonium oxide...lol... nitrogen monoxide or dioxide are more like it.

Have tried this myself, it worked as follows:

Bubble air through 25% ammonia, dry this over fused CaCl2 (U tube), and feed this into a tube that is heated from the outside with a glowing electrical wire (or flame I suppose). Inside there's 10cm of wound up Pt wire which was obtained from the jeweller and hammered as flat as possible. With a supersimple setup like this, and a constant and adjustable air flow, the Pt can be made to glow red without outside heat. ON the exit side you either get white
ammonium nitrate fumes or NO2, which is brown.

The reaction is

NH3 + O2 --> NO + H2O -> NO + O2 --> NO2 (not balanced)

This is called the Ostwald Process.

http://en.wikipedia.org/wiki/Ostwald_process

Ramiel - 10-10-2006 at 16:34

To demonstrate the catalytic activity, you might want to show the reaction (or lack thereof!) without the platinum, then upon adding the Pt, the reaction magically begins. Then I suppose you would weigh the Pt to show it hasn’t been consumed. Needless to say this ought to be performed in a fume cupboard.

Sorry to post semi off-topic, it occurs to me that this could be a superior way to get NO<sub>2</sub> than the HV arc method which makes up the <a href=http://www.sciencemadness.org/talk/viewthread.php?tid=1518>Birkeland-Eyde</a> reactor (I always thought the HV arc was more inefficient and fiddly on the amateur scale than really needed). The main question would be exposure time over the catalyst. Possibly coiled lead tubing with flattened Pt wire or flakes <i>etc</i>.?

12AX7 - 10-10-2006 at 16:38

You could keep the platinum coil electrically heated.

Tim

Jdurg - 10-10-2006 at 18:06

A good one is the use of platinum as a catalyst in the combusion of hydrogen and oxygen. Just take a balloon and fill it 2/3rds with H2 and 1/3rd with O2. Using a steel needle, pop the balloon. Nothing will happen.

Now take a balloon and fill it 2/3rds with H2 and 1/3rd with O2. Using a piece of pure platinum wire, heated up a bit in a bunsen burner flame until it is warm but not hot, pop the balloon. The warm platinum wire will catalyse a reaction causing a very quick and very loud 'KABOOM' as the H2 and O2 react. This happens basically at room temperature and is simply amazing to see. You don't think that the presence of a simple metal can cause a reaction to proceed like that, but it does.

craynerd - 11-10-2006 at 12:52

Thanks for your replys! Really excellent stuff.

Jdurg, i am interested in your idea. Would the same work with a purely hydrogen only balloon, obviously reacting with the oxygen in the air?

I have slight concerns with exploding H/O mix 2:1 as a demo due to safety...bla bla...

If not, then i may have a try myself with the experiment you detailed and just check out the volume. I have an oxygen cylinder but my only method of H2 production is using acid + metal in a narrow neck conical flask, overstretching a balloon onto the neck and waiting for the pressure to blow it up. I successfully use this method and with relative ease (15 minutes or so) i can get a balloon half blown up. Haven`t a clue how i could get a mix ?? suggestions?

Thanks

Cray

Jdurg - 11-10-2006 at 17:34

I would start out on a small scale. It may work with just H2 and atmospheric oxygen, but I'm not sure. Still, going on a small scale would be a good idea. Perhaps just take a test tube filled with H2 and use warm Pt wire to ignite it?

craynerd - 12-10-2006 at 08:54

Igniting with warm Pt wire ? What will H ignite without a flame or what do you mean? Sorry for my ignorance!

Chris

Jdurg - 12-10-2006 at 10:29

Hydrogen and oxygen will ignite thanks to the catalysis of the platinum wire. You don't need a flame. Just the presence of platinum in a H2/O2 atmosphere.

not_important - 12-10-2006 at 23:41

Quote:

Originally posted by craynerd
Igniting with warm Pt wire ? What will H ignite without a flame or what do you mean? Sorry for my ignorance!

Chris

At one time there were various platinum based ignitors for stoves and lights using water gas or town gas, which contain enough H2 for the catalytic effect of Pt on H2 + O2 (air) to generate enough heat to ignite the mixture.

I believe Oliver Sacks mentions this in Uncle Tungsten. Such devices were more common in Europe and N.E. US cities than in the rest of the US; you can still find old ones being used in some areas, pizoelectric or house mains drive sparkers have replaced the platinum devices in newer gas burning products.

craynerd - 13-10-2006 at 04:05

Ok, I just tried two experiments and neither worked.

Firstly i went for a simple hydrogen pop, acid+metal in a test tube. Collected the gas literally with my thumb over the end, popped with a lit splint. I tried it next using platinum which i warmed up in the Bunsen. Nothing happened. I tried it several times, I even coiled my platinum wire to get more area in the test tube within the mixture. Nothing!

Next i used electrolyisis of dil. sulphuric acid and collected the gases, piped them through washing-up liquid to collect the bubbles. This time it was obviously stochimetric quantities of H2 and O2.
Ignited with a lit splint and the mixture exploded. Repeated but instead i inserted the warm platinum wire. Nothing!!

Whats going on, AKA what am i doing wrong?

Help appreciated, this would be great if i could get it working.

Chris

[Edited on 13-10-2006 by craynerd]

craynerd - 15-10-2006 at 01:00

anyone?

not_important - 15-10-2006 at 01:16

Higher surface area means more reactions per second. If the wire is very smooth the overall rate may be too low.

Sorry I don't remember any details, but I've read of an electrochemical method to roughen the wire - beleive it was an AC electrolysis trick.

Note that we're talking roughness on a scale below what sandpaper does, but you could try a quick rub with very finnd sandpaper to see if it made any difference.

The_Davster - 15-10-2006 at 08:53

You can also heat methanol or ethanol up till its steaming in a beaker, and then hang a coiled platinum wire over which is previously heated to red heat in one spot. The red glow on the platinum will grow until the alcohol catches fire.

The reaction that occurs before the alcohol catches fire is oxidation to the aldehyde.