Back to Hydrogen Experimentation

[zking786]

I've continued my hydrogen production experimentation, and am now re-trying some of the techniques I've been told...

 

1. Mix NaOH and Al foil in water to produce hydrogen gas. Unfortunately, though I get rapid bubbling (some times even minor explosion when contained), I can't ignite the produced bubbles. I'm using a gas-stove lighter and I can't even hear the slightest 'pop'. What could be going wrong?

 

2. I was told that HCl + Al in water will produce hydrogen gas. Is this true? It doesn't make sense to me. Should it, or do I have to add CuSO4 or CuCl to the mixture?

 

 

Also, I've been wondering how I can remove the oxide coating that forms on Al. If I could, perhaps, recoat it with something that dissolves in water, but prevents the formation of an oxide on the surface, then I could create a non-corrosive, safe hydrogen-production setup.

[YT2095]

you`ll probably find that in you Al and NaOH apparatus the gas was wet, also if the H2 is in Large excess it won`t ignite, I sincerely hope you didn`t do any of these tests in Sealed containers!?

if you DO then bubble the gas through a water trap, that way is it Does catch fire, it cannot back-up into your reaction vessel.

 

as for the Al and HCl soln, you don`t Have To to add a copper salt, but it helps jump start the reaction alot better, you don`t need to add much either.

 

Both of these reaction get Very Hot! so don`t overload it with alu until you`re sure the rate of reaction is stable and has plenty of room for expansion.

[zking786]

Interestingly, when I did the NaOH experiment, it got hot (warmer than I'm comfortable touching), but not "very hot". Is this normal?

 

Why wouldn't hydrogen in excess NOT ignite? Not enough oxygen around it to create an explosion?

[YT2095]

yes it Is normal, it all depends upon the concentration of your soln, the amount of Al added in a given time etc...

 

if you have Pure Hydrogen or Methane or any other flamable gas in extreme concentrations it will not burn until there is sufficient oxidiser present.

 

here`s a Head scratcher, IF you were in a room full of 100% butane gas, what fuel would you need to put in your lighter to get a flame?

 

Answer: Compressed air!

[Tannin]

Just to give the more accurate wording to the forementioned gas concentration required for explosion:

The technical terms are:

HEL - Higher Explosion Limit

LEL - Lower Explosion Limit

i.e. an explosion may occur only when the substance concentration is between these limits.

Usually you can find these data in MSDS - Material Safety Data Sheet. They are freely available on the web and are "must" before you are going to perform your experiment.

For example:

http://www.llnl.gov/es_and_h/hsm/doc_18.04/doc18-04.html#2.0

According to this source:

"Hydrogen has an unusually large flammability range. It can form ignitable mixtures between 4 and 75 percent by volume in air. The range for explosive mixtures is also very broad. Given confinement and good mixing, hydrogen can be detonated over the range of 18 to 59 percent by volume in air. The energy content per weight of a stoichiometric mixture of hydrogen and air is about the same as that for the explosive TNT, although much less energy is converted to pressure waves during detonation."

Good luck and be careful!

[zking786]

Maybe if I had raised the lighter a bit higher, I would have had a high enough oxygen concentration to ignite the hydrogen?

[raivo]

Hydrogen flame emits very little light. If hydrogen happens to burn without explosion then fact of combustion may remain unnoticed.

[YT2095]

that would help, also if it`s in an open dish or something not contained or fragile, add a few drops of detergent, the bubbles will hold the hydrogen in place for a while and you`ll get a better effect, a rapid cascade of popping sounds

[CPL.Luke]

about the whole ensuring that the flame doesn't back up into your reaction vessel thing, do make sure that it doesn't, although entertaining as the explosion may be, the rapid burning sensation felt afterwards as the HCl hits is not.

 

trust me

 

I think my chem experiment was zinc something and HCL to produce hydrogen gas.

[YT2095]

worse still is the NaOH type, HCl can be much more forgiving towards humans than Caustic Soda.

 

Given the Choice that is

[zking786]

I touched my NaOH-water mixture and it wasn't that bad. Initially, I couldn't really feel anything. Later, it burned a bit and I had to wash it with water, soap, and N/10 HCl. It still feels a bit powdery, so I might still have some on my hands.

[zking786]

I've done both experiments and find the 10% HCl+CuSO4+Al to work best. I have some questions, though.

 

1. What is the brown-black residue?

2. What does the CuSO4 do?

3. Why does the reaction slow down even when I add more Al? It only seems to speed back up when I add 10% HCl. I thought HCl was a catalyst.

[YT2095]

the Copper Sulphate is a sort of catalyst here, it helps breakdown the Alu oxide layer and works after as displacement action, the brown/black will be the copper PPT as an oxide (copper II Oxide I beleive).

although some will remain in the soln as the Chloride.

adding more alu probably just serves as a cooling effect for the most part, and don`t forget as the reaction progresses, the less effective the soln will be as it`s being used up!

don`t worry about the copper PPT, it`s still doing its job, it works as a kind of Battery that`s being shorted out to put it simply

[zking786]

So what exactly is being used up? Is it the HCl or the Al. From your previous response, it seems that the CuSO4 is a catalyst (and is therefore not being consumed).

 

If I wanted to produce hydrogen constantly, how would you reccommend I proceed. What should be added to the mixture? I've got a cooling setup in place, so that won't be a problem.

[YT2095]

the SO4 is incidental, it`s only an ion carrier to make the Cu soluble

consumed is the Al an Cl ions, forming alu chloride.

the H on the HCl has to go somewhere, that is what you harvest

[zking786]

Thanks for that explanation. It makes sense now.

 

So, what happens in the NaOH reaction?

[dna mauro]

NaOH + Al doesent make sense to me..

NaOH + Al =Al2O3+Na+H2 ... but that kind of reaction shoudnt work.

Best way to produce hydrogen is by using strong acid and active medal, like H2SO4 + Zn.

Also if you want to separate oxygen and hydrogen, than use electicity.(electrolysis ???). one is anode, other kathode so you can collect hydrogen(pure) and oxygen, but beware about 3l of both collected(collected together), is very powerful...

[zking786]

That's interesting...

 

So the hydrogen produced is from the hydrogen in NaOH? I thought it was from the water in the NaOH solution. Also, is the Na in ionic or elemental form (does it gain an electron in the mentioned reaction)? Are you sure that your reaction is correct? I've heard of Al forming a compound with an OH group, not an oxide.

[YT2095]

it makes sodium aluminate, and Hydrogen.

[raivo]

In my opinion NaOH is much better. To make 3 mol of hydrogen you need 80g NaOH or aproximately 0.65l concentrated (33%) HCl. What is cheaper? What is easyer to get? In my case NaOH.

 

[math]

\ce{2Al + 2NaOH + 2H2O = 2NaAlO2 + 3H2}

[/math]

[math]

\ce{2Al + 6HCl = 2AlCl3 + 3H2}

[/math]

 

It is good idea to be cautious and wear some eye protection as NaOH can be much worse to your skin than HCl -is.

[gcol]

I have made some cells using Al, Cu, NaCl, and NaOH. To each 2litre electrolyte capacity cell I occasionally add 5ml of NaOH at 10% concentration to depolarise the Al and boost the voltage from about 600mv to 1,25v (at a steady 40ma per cell for about 50% voltage drop) to charge nicads. A fair amount of hydrogen is produced, depending on the current draw. I was considering collecting the hydrogen as an energy by-product, but the additional "engineering" is rather fiddly.

 

If I work the cells with no NaOH, I still generate apreciable hydrogen, so NaOH is not strictly required.

 

When the cell needs "rejuvenating", a white gell that hardens in air forms on the aluminium. A little NaOH removes this, a white precipitate falls to the bottom of the cell, and away we go again.

 

As a matter of interest, not all aluminium is pure. Drink cans for example, and some aluminium food trays, are alloys and produce varying colours and types of precipitates and flocculants that settle out at different rates.

[zking786]

Could you post the reaction equation for the Al + HCl + CuSO4, for clarity. The balanced equations make the reactions seem so much simpler.

 

So, is the murky solution and the black-coated aluminum the NaAlO2 and AlCl3 from the reactions?

[jdurg]

NaOH + Al doesent make sense to me..

Aluminum metal is a VERY reactive metal. Much moreso than most people think. (As we see it used all the time in outdoor structures, soda cans, baking, etc.). Many people don't realize that aluminum metal is covered by a very tightly bonding oxide coating which protects the metal from further reaction. This oxide layer is insoluble in water so you don't think of aluminum reacting with water.

 

The thing is, aluminum is up there with sodium and potassium in terms of reactivity with H2O. You just need to remove the oxide layer. Sodium hydroxide is able to remove the oxide layer given enough of an induction time. Now, the aluminum metal is readily available for reaction with water and you get copious amounts of hydrogen gas forming.

[jdurg]

Oh yes, one more thing. Be VERY careful with NaOH on your skin. It is MUCH more nasty than HCL, or most other acids are. The reasoning is that NaOH will readily saponify the fats just benath the layer of dead skin cells on the surface of your skin. You really won't even feel this happening all that painfully. It will typically just be a slight warming and tingling sensation, but later on it will REALLY begin to hurt.

[woelen]

Could you post the reaction equation for the Al + HCl + CuSO4, for clarity. The balanced equations make the reactions seem so much simpler.

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.

 

So, is the murky solution and the black-coated aluminum the NaAlO2 and AlCl3 from the reactions?

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.