Not-so-simple Electrolysis

[zking786]

I was trying to perform electrolysis using a smart charger and a battery eliminator in series (generating about 12V 1A). The EMF setup was connected to two aluminum electrodes which were submersed in brine solution. The intent of the exeriment was to obtain pure hyrdogen gas and a residue of an oxide of aluminum. I got something quite different...

 

I found that the gases weren't flamable and thus couldn't be oxygen or hydrogen. A light-bluish/white precipitate was formed slowly at the surface. Over the course of the experiment, some of the solution must have mistakely spilled (due to my handling, since there wasn't any rapid bubbling). This water, when cleaned off the clear-coated table, left a faint blue residue on the otherwise dark wooden surface. Finally, the aluminum electrodes were barely worn (1 cm diameter was unchanged), and I ran the electrolysis for about an hour.

 

The results have posed the following questions:

1. What could the gases that were produced be?

 

2. What could the precipitate formed be?

 

3. How can I remove the barely-noticable light blue stain from the table? Interestingly, it isn't some sort of crust on the surface, it seems like it has actually stained the clear coat.

 

4. What can I do differently to produce hydrogen? Why doesn't this apparatus produce hydrogen?

 

 

Any help will be greatly appreciated.

 

Thanks!

[woelen]

The gas you obtained definitely must be hydrogen. Probably you did something wrong with testing its flammability (letting the gas escape into the air, before you made it burn).

 

The precipitate most likely is Al(OH)3. At the anode, aluminium dissolves, giving Al(3+) ions. With hydroxide, formed at the cathode, this forms Al(OH)3.

 

The light blue stain you have also most likely is finely dispersed Al(OH)3, which is absorbed by the wood somewhat. The spilled liquid contained water, NaCl and Al(OH)3. It may have been absorbed somewhat by the wood and fine particles of Al(OH)3 may now be inside the wood. This is not a good thing. It will be hard to get it out. Using chemical means like dilute hydrochloric acid may help getting the insoluble Al(OH)3 out, but I'm not sure what it does with the wood and the laquer on the wood. To me, that does not sound as a good thing.

 

Very finely dispersed white flocculent solid, such as the Al(OH)3 may have a somewhat bluish appearance. Think of cigarette smoke, which by no means is blue, but with certain light conditions, it looks blue. This effect also causes the very light blue color of the precipitate and the color of the stain on the table.

[zking786]

So the Na+ and Cl- ions aren't oxidized or reduced?

 

Also, in retrospect, the precipitate wasn't really blue. It was a white foam. Does this change anything?

[woelen]

Indeed, the Na(+) ions and Cl(-) ions are not oxidized or reduced. You can oxidize the Cl(-) ions when you use a graphite anode.

 

The precipitate IS white, but sometimes it looks a little blue, just as cigarette smoke sometimes looks blue, while in reality is not blue. So, nothing changes with my story.

[zking786]

Thanks for the help!

 

What about if I want to produce hydrogen gas only (no chlorine gas or oxygen, just hydrogen). I thought using aluminum electrodes would allow me to create an oxide of aluminum and hydrogen gas only.

 

How do you know which gases are created at the electrodes? Is there a chart you're using?

 

Thanks for the answers.

[woelen]

How do I know this? Because I read some books about this subject and I studied it . This is very basic chemistry.

 

At the cathode you usually obtain hydrogen gas and at the anode the reaction products strongly depend on the electrode material and on the electrolyte (the dissolved salt). Metal anodes dissolve, giving the metal salt, except for the very noble metals and for niobium and tantalum. With graphite anodes (and also noble metal anodes like platinum, iridium, osmium) you obtain oxygen at the anode, or free halogen, when an halogenide is used as electrolyte.

[zking786]

That's interesting, I heard that if you use a carbon electrode (the type used for welding) you can create CO2 gas and H2 gas. Anyway, what other inexpensive electrode combinations would you recommend if I'm trying to produce hydrogen only (no other gases)?

 

On a side note, woelen, you seem to be fairly experienced in inorganic chemistry. I was wondering if you know what type of alloy or compound I could deposit in water to safely produce lots of hydrogen inexpensively. I've heard of a nickel and sodium based solution, but I can't remember the name. I've seen an experiment where a guy dropped a pelet of some alloy into a container of water (not electrolyte solution) to produce lots of hydrogen. He had said that the alloy was really cheap--I just can't remember the name! Any ideas?

[woelen]

If you want to make hydrogen in a safe and inexpensive way, then I would go for dissolving aluminium foil in dilute hydrochloric acid (appr. 10% HCl works fine), to which a small amount of a copper salt is added.

 

The following procedure makes hydrogen gas nicely and safely and requires no other chemicals than those available everywhere at low cost.

 

1) Take 100 ml of dilute hydrochloric acid (10% HCl), do not take the concentrated stuff.

2) Take two copper wires (electricity wire is OK) and perform electrolysis of the hydrochloric acid with these at a few volts. At the negative pole some hydrogen gas is formed, the positive pole dissolves. Don't bother getting the hydrogen gas of the negative pole, this is not why we want this electrolysis. We want this electrolysis because of the copper salt, which dissolves in the hydrochloric acid. Perform the electrolysis, until the liquid has a nice green color.

3) Add some aluminium foil to the green solution. You will have instant evolution of a lot of hydrogen gas and heating up of the liquid.

 

If you have access to copper sulfate or copper chloride, then you can skip the electrolysis step. Then dissolve a few spatulas full of copper sulfate or copper chloride in the acid and then add the aluminium foil.

 

------------------------------------------------------------------------------------

 

I also know some alloys, which give instant hydrogen production, when added to water, but, although these are not expensive (speaking industrially), these by no means are OTC materials for individuals. These alloys are based on sodium metal and that is not a material you can easily find. The method, described above can be done by everyone.

[zking786]

I'll try the HCl method you recommended. Could you also tell me about the alloy-based methods? I'll be going to a large chemical supply store and can probably either purchase or create the alloys. Also, what do you mean by OTC?

[YT2095]

OTC = Over The Counter.

[zking786]

For some reason the described experiment didn't work. I used two different copper wires and plenty of EMF, but still didn't get a green solution. When I added Al, I didn't even get a reaction. I did, however, find bubbles at the cathode. A black coating formed at the cathode and a white/clear one formed at the anode. What happened?

[YT2095]

after reading this, I set the same up myself, I`m using 12.3% HCl at 2 volts, there`s No black color on any wire, there are bubbles at the cathode, and a white(ish) material flowing down the anode (that`ll be the copper salts).

 

nothing Blackened though?

 

edit, I just cranked up the power to 5.5volts, plenty of Bubbles (still nothing black or dark) the anode discoloration (like smoke falling) has a slight grey/green tinge.

 

EDIT:::: Stop the Press::::

 

he`s perfectly right, as soon as that "Smoke" like liquid migrates from the anode to the cathode along the bottom of the vessel, the cathode does indeed turn black, and the soln isn`t what I`de call green either in all honesty, I`ll leave it to run and see what happens anyway, but yes, Zking786, I`ll confirm your observations on those happenings also

[zking786]

Thanks for the confirmation, YT2095.

 

For clarification, I've been using a 12V charger (gives about 17-18V pd). Maybe that's why I didn't notice the smoke-like liquid migrating from the cathode to the anode -- it just happened too quickly.

 

Any idea what's going on? If a copper salt is formed, why doesn't the copper chloride solution produce hydrogen at the addition of Al?

[woelen]

Electrolysis is quite a slow process, if you wait long enough, then the liquid will turn green (or light green/blue). The white material most likely is CuCl, formed at the anode. This is white. It dissolves in the HCl and will be oxidized quickly by oxygen from the air to a copper (II) compound. Once your solution is greenish, you'll have lots of H2 almost at once from your Al-foil.

 

The black coating at the cathode must be copper metal, in the form of a spongy mass. In that way, it looks very dark.

 

Try to avoid as much as possible that the white material from the anode reaches the cathode. What you can do is wrap a paper tissue very loosely around the cathode, such that there is no free flow of liquid around the cathode, but still with sufficient room around it, to let all bubbles escape.

 

Your outcome surprises me, I've done electrolysis of HCl quite some times myself with copper electrodes and it worked like a charm. I must admit, however, that I used concentrated HCl, which I diluted after the electrolysis.

 

YT, do you have some CuSO4 or CuCl2? If you have that, add a pinch of this to some dilute HCl (10-15% is OK), dissolve this, such that you get a green solution and then add the Al-foil. The result is really stunning! If you do the same without the copper salt, then the Al only reacts after a long induction time.

Even stronger, this experiment even works with plain NaCl instead of HCl, if some copper salt is dissolved in the NaCl as well! The Al dissolves in the solution of NaCl with a lot of hissing, evolution of a lot of heat and formation of a lot of hydrogen gas! I'm not kidding, this really is true!

 

http://woelen.scheikunde.net/science/chem/exps/cu+al/index.html

[zking786]

About how many hours do I need to run the setup? Say I'm pumping in .75A at 17V, how many hours till I will get the green solution you speak of?

 

While I have Dilute N/10 HCL, what other cool experiments can I perform?

[woelen]

While I have Dilute N/10 HCL, what other cool experiments can I perform?

You only use an N/10 solution? I was speaking about 10% by weight. N/10 is VERY dilute (only appr. 0.35%).

 

With a 10% HCl solution and a current of 0.75A you should have a nice green solution within an hour or so.

 

HCl can be used to make carbon dioxide in large quantities with baking soda. With chlorine bleach you can make green chlorine gas, but beware, the latter experiment MUST be done outside on a windy day, with wind from behind. Chlorine gas is very toxic. The experiment, however, is very nice and chlorine gas can be used for many other interesting experiments (such as burning iron wool, or fine copper wire with yellow/brown smoke).

[vanillity]

fill a water balloon with hydrogen and throw it at the ground, you'll get some cool effects, the balloon feels like a regular air filled balloon but when it hits the ground it ripples. (worked for me)

[jdurg]

fill a water balloon with hydrogen and throw it at the ground, you'll get some cool effects, the balloon feels like a regular air filled balloon but when it hits the ground it ripples. (worked for me)

You realize that hydrogen is a gas, and that a water balloon is a balloon filled with water. If you displace the water in the balloon with hydrogen you will have a balloon that will float up and away. So what you've said really makes no sense at all.

[akcapr]

wwwhat the heck is he talking about