Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: aarothepharo on July 10, 2008, 09:34:02 PM
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I know many of you are tired of seeing all these posts about the electrolysis of water so lets talk about catalysis.
I have been expirementing with electrolysis of water lately just for a fun cheap project.
Using stainless steel electrodes and water from the tap (perhaps I should have used distilled ;D) I used a power supply to start divding molecules of water.
Using common table salt as a catalysis (helps the water conduct eletricity)..the water over time turns a nasty charcoal color.
Using sodium bicarb as a catalysis...the water over time deveopes a thick layer of white foam that floats on top of the water.
Is there any catalysis I can use to keep the water in its normal state? something hopefully easy to obtain. one person told me sulfuric acid but I rather not use that.
Please Help,
Aaron
PS when using the salt I never did see any oxygen bubbles rising from the + side. I only saw them in the bicarb reaction.
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Salts are not catalysts, they are just there to decrease solution resistance. NaCl will slowly loose chlorine (electrolysed out from the solution together with oxygen) and you will be left with the solution of mostly NaOH, if it contact with air this will probably adsorb CO2 and you will get some mixture of carbonate/bicarbonate or NaOH/carbonate. Using bicarbonate you don't risk Cl2 evolution.
You may try to start with water acdified with sulfuric acid, or with water with NaOH, although the latter will sooner or later become just some combination of base/bicarbonate/carbonate.
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Ok so I need to review my chemistry terms... so am I understanding right?
the NaCl (salt) is losing the Cl but the sodium is combining with O and H. Is that right?
so I have NaOH.....H2O.....and....Cl2 ?
Is the Cl2 in the form of a gas?
in the Bakinging soda reaction the bi carb is completely dissolved so where does the foam come from?
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There are three reactions that go on. Two competing on anode:
2Cl- -> Cl2(g) + 2e-
4OH- -> 2H2O + O2(g) + 4e-
(they are nor exactly competing, it is more complex, but we may start with explanation that as long as chlorides are present in a reasonably high concetration chlorine will evolve together with oxygen).
One on cathode:
2H+ + 2e- -> H2(g)
No idea about the foam. My first idea is contaminants/surfactants.
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Ok I think I get it but where is the Na going from the salt I see where the clorine went?
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No idea about the foam. My first idea is contaminants/surfactants.
It's CO2 caused by the reaction of localised hydronium ions (caused by the reaction of ferric ions with water) at the anode with the bicarb.
Aside from the anodic processes you mention, with a steel electrode, and depending on both your cell geometry and reaction velocity, the applied potential can cause the iron to oxidise to ferric ion (as I discuss on another thread).
I'm only a newcomer to this forum myself, but the plethora of people (and threads) now talking about this same subject is becoming a little tedious.
Mostly they are newcomers, and mostly they know almost no chemistry. They call electrolytes catalysts, ask questions about ridiculous electrolytes such as bicarb, and don't understand answers when they are given.
Anyone who is involved with any automotive forums will know that these threads are now legion. Everyone, it seems, is interested in saving money by bolting an electrolysis cell onto their engine. Anyone who understands the science behind this idea that questions the testimonies that accompany these claims, is shot down in flames, with arguments that usually boil down to
1. We haven't heard about this because big oil has stopped it (usually with an accompanying story about an inventor who was mysteriously murdered by Big Oil)
2. The laws of thermodynamics are made to be broken (I kid you not) :P
3. You don't know if you don't try. Those of us with a formal science education are "stuck in our thinking" and don't know how to try new ideas.
4. Anything that's on the internet must be true. Anyone who doesn't believe in the existence of molecules such as HHO and monatomic hydrogen (at STP) has been brainwashed by their formal education.
And so, what is happening is that now some people who have believed that they can knock up in their garage a device that will produce results that the combined efforts of the world's best automotive engineers cannot, have actually tried some of these devices.
And, now that they have discovered that they don't work, they think "oh - I know - I'll ask some scientists - they'll be able to answer all my questions."
So, to anyone in this category, let me give you a hand. It won't work. I have a PhD in electrochemistry, and I can tell you that the design of electrolysis cells is a hideously complex science, with concepts such as overvoltage, junction potentials, ionic mobilites and diffusion coefficients, Butler-Volmer equilibria, interfacial electron transfer kinetics, electrode resistivity and potential gradients, etc., etc.
But you don't need to understand any of this to know that it won't work. I'd have thought that the complete absence of this technology on any car currently being built or proposed would make it obvious to anyone whose IQ was greater than that of an apricot that it won't work.
To come onto this forum and to expect to be able to ask how to build one of these devices with a few tips is like a kindergarten child asking for tips on how to build a space shuttle.
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No idea about the foam. My first idea is contaminants/surfactants.
It's CO2 caused by the reaction of localised hydronium ions (caused by the reaction of ferric ions with water) at the anode with the bicarb.
Are you trying to tell us that evolving CO2 makes foam, but evolving hydrogen and oxygen don't? I am not aware of any reason why this is going to happen. Foam is created when the water surface tension is low enough (hence surfactans contamination), in general it doesn't matter what gas evolves.
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Okay Mr. Mark Imisides
I feel we agree on some aspects and then disagree on some.
I do agree that that the big oil companys distroy all ideas to save money or get off of gas completely. I also agree in a couple more aspects.
But
1. If you where to read my first post you will see that I said I'm only doing this as a fun project. I have no motive to bolt this thing to my car. Even if you are posting that to anyone else who may see it, why in the world did you put it in my thread. You had to shoot down my post about a fun little project to stop others from building a HOD (Hydrogen on demand) system for there car? Post your comment in someones thread who actually says they are building one.
2. Also I know a medium-high amout of chemistry I just post here to double check some of my observations. I felt like in your post you were shooting down my knowledge of chemistry. Being a PhD of electrochemistry you probably know more about the subject than I. However, that does not give you the right to crack upon people for not knowing as much chemistry as you. For say, when you said "Mostly they are newcomers, and mostly they know almost no chemistry".
I Understand I called the NaCl and the Sodium bicarb a catalysts. It was late when I was posting my first post so My head called it a catalysts and not an electrolyte.
Now I understand that everyone is getting a little tired of hearing all these posts about the electrolysis of water. I see myself that a lot of people are posting this very subject, but in my first post the first line I wrote was "I know many of you are tired of seeing all these posts about the electrolysis of water "
If a PhD is going to make you do this, you might as well give it back.
Now if you would like to help me in my simple little project feel free to help.
Aarothepharo
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I agree with him ;D
No one said he was trying to use it on his car, so if you aren't here to help him with his experiment keep your negative, no it all PhD attitude out of this particular thread!
<3
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As a Citizen Scientist, I take offense at some of Mark Imisides New Member remarks. Obviously he is ranting, but he did it on the wrong thread. Although this thread may have been put in the wrong forum. I thought that typical entries here are for people asking questions for their general chemistry course (college implied), but we do not discourage other posts.
I have to agree that many of the hydrogen claims are bogus. But a Ph.D. discouraging experimentation for knowledge sake is abysmal. I hope he apologizes. By the way, I can point him many threads he should have put his post on.
I wish for Mark Imisides New Member to answer Borek surfactant reply to his post.
Aarothepharo - although based on some of your post my opinion of your chemistry knowledge is not the same as yours, please keep trying. Also I am sorry to have slightly hijacked your thread.
Some additional notes - I would try different electrodes than ones with iron in them. The most common one seen on responsible web sites are carbon based from batteries.
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ok back to the post...what is a good electrolyte to use? Something that will greatly reduce the resistance of the water.
I can support up to 5 amps at 12V (its a car battery charger). Also some of you have said that stainless steel is not the way to go because it oxidizes. But I thought Stainless steel will never rust!!! Ok so Carbon electrodes? Like maybee Graphite? Remember Graphite has a resistance to electricty.
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The most common one seen on responsible web sites are carbon based from batteries.
The handbook on chemistry and physics has tables involving potassium and other chemicals. I always thought commercial systems used sodium, but I could be wrong. Also, if I remember correctly, there is a limit to the amount of electricity that will produce a good result.
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Whoa!!!!!!!!!!!! Potassium and Sodium
Those are alkali metals Mr. They dont mix with water so well...so carbon rods in batteries are good for the electrodes?
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I am sorry, I misspoke. The potassium and sodium are in compounds such as potassium hydroxide and sodium hydroxide.
Yes, carbon rods – like I said do a search here or Google to see what they do
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Ill look into the carbon.
Sodium hydroxide is caustic soda or lye...a little dangerous. But "The Works" toilet bowl cleaner is 20% NaOH so ill mix some in and hope for the best. The extra 80% is the problem. They might be bad contaminates.
KOH is another form of lye....I dont know where to get it as easily as the NaOH
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Check out the sources used by people who make soap as a hobby.
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No idea about the foam. My first idea is contaminants/surfactants.
It's CO2 caused by the reaction of localised hydronium ions (caused by the reaction of ferric ions with water) at the anode with the bicarb.
Are you trying to tell us that evolving CO2 makes foam, but evolving hydrogen and oxygen don't?
Correct. The reason is that the former is a homogenous reaction whereas the latter is a heterogenous reaction.
One of the many points about electrolysis that most people on this thread don't appreciate is that the formation of gases at a solid electrode from an aqueous reactant is a hideously slow and inefficient process. The overvoltage for the these processes is huge. For a typical electrolysis reaction the potential difference between the E0 and the potential at which electrolysis occurs is of the order of 300-500 mV. For hydrogen evolution, dependent on the substrate that is used, it is of the order of 700-800 mV.
In the early days of electrolysis, this was referred to as a "bubble overvoltage", and interpreted in terms of the work required to form the bubbles. In recent itmes, however, it is explained in terms of interfacial reaction kinetics, specifically the rate at which electrons transfer across the heterogenous interface. Thus, overvoltage is related to the equilibrium current exchange density.
Bottom line is this - formation of bubbles at electrode interfaces is such a slow process, and influenced by so many variables, that calculations of reaction rates (or Faraday's law) are extremely complex.
The reaction between the H+(aq) and bicarb ions, on the other hand, is an extremely fast process that produces a great deal of effervescence. One of the qualitative tests for carbonate or bicarbonate ions, as I'm sure you're aware, is the addition of a small amount of acid - instantaneous effervescence being the result.
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One other thing - the bubbles formed by a heterogenous process are big - they don't dislodge from the electrode surface until their buoyancy overcomes their adsorptive attraction to the electrode which, depending on the surface energy of the electrode, can be quite large. The outcome of this is that bubbles formed at an electrode surface are usually large enough to actually see.
Bubbles formed by a homogenous reaction on the other hand, are so small that all you see is the foam that they produce (the result of the massive surface area of the air/liquid interface)
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Sorry, but your explanation to the foam creation doesn't make sense to me. First of all, OP told us:
Using sodium bicarb as a catalysis...the water over time deveopes a thick layer of white foam that floats on top of the water.
Over time, so it is building up, it is not a thing present all the time, it is not a thing that appears at the very beginning. It is not kind of a short lasting foam you are probably referring to (at least that's what I can guess form your description).
Second, amount of bicarbonate in the solution is limited, so (assuming it is a simple acid base reaction) it will be a problem only at the very beginning. Again, from the description it is not.
Third, overvoltage has to be taken into account when designing cell and calculating its parameters, no doubts about it, but we are talking about using voltages that should be easily able to overcome the problem. That means that the main limiting factor is the solution resistance which limits current we can use.
Finally, you suggest that H+ is produced by the reaction of Fe3+ with water:
It's CO2 caused by the reaction of localised hydronium ions (caused by the reaction of ferric ions with water) at the anode with the bicarb.
While it is very likely that electrode corrodes, it is not a fast process, so amount of H+ produced will be low, for sure not high enough to make bicarbonate react as fast as you seem to suggest. We have several processes taking place, let's concentrate on two of them. On the anode dissolution of iron, followed by the carbon dioxide evolution:
Fe -> Fe3+ + 3e- (not necesarilly one step, but it doesn't matter for our calculations)
Fe3+ + 3H2O -> Fe(OH)3 + 3H+ (probably much more complicated, as there are many complexes involved)
3H+ + 3HCO3- -> 3H2O + 3CO2
bottom line is - 1 electron used for corrosion, one molecule of carbon dioxide.
On the cathode:
2H+ + 2e- -> H2
2 electrons, one molecule of evolving gas.
Even assuming that there are no other reactions but iron dissolution occuring on the anode, amount of carbon dioxide evolving will be only twice larger than the amount of hydrogen evolving. This is not as huge difference in speed as you suggest, and that's only assuming there is no oxygen evolving at the anode at all. There is oxygen evolving and anode corrosion is a slow process, so amount of carbon dioxide evelving should be much, much lower.
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Mark Imisides New Member -- Do you have examples of gas or liquid electrodes that are currently being used for this process?
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Ill look into the carbon.
Sodium hydroxide is caustic soda or lye...a little dangerous. But "The Works" toilet bowl cleaner is 20% NaOH so ill mix some in and hope for the best. The extra 80% is the problem. They might be bad contaminates.
KOH is another form of lye....I dont know where to get it as easily as the NaOH
No no no. 'The Works' is Muriatic Acid, 20% by weight HCl in aqueous solution - no contaminants. Just a heads up.
And I believe KOH is in stump remover, not positive though.
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Some types of drain cleaners are NaOH based. Either H2SO4 or NaOH in these things, both can be used as an electrolyte in water electrolysis.
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I have never made soap from scratch except in a class laboratory.
But, there are many hobbits that do make soap.
I Googled "soap making sodium hydroxide" and selected this site.
Potassium hydroxide is known as caustic potash
Sodium hydroxide is known as caustic soda
http://www.thesoapdish.com/caustics.htm
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i wonder is a hobby or craft store carries NaOH.
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possibly, but NaOH = oven cleaner.
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nj_bartel
how pure or is that even important
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TO EVERYONE READING THIS POST...Im going to switch to carbon rods for electrodes so we dont have to worry about IronOxide. Is carbon rods ok with everybody?
If you are still actively participating in this thread please post a list, in your opinion, of electrolyts that you think may be a good choice. I will pick the most popular answer and try it.
Ill run the expirement again when I get the Carbon rods. Unless anyone has an objection to the carbon.
Please everybody submit a list.
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nj_bartel
how pure or is that even important
Pretty sure some of them come as pure as you can make it, while others come with scouring agents.
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This guy used carbon rods
See how he got them from old batteries
http://sci-toys.com/scitoys/scitoys/echem/echem.html
I take it you did not search this forum or the web as I suggested
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When I was young, I used graphite rods from two dynamos as electrodes for electrolysis of salt water. But for some reason the graphite rods dissolved. Huh, how curious is that?
I also tried tin and even nails. But they made stinking soup of something.
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Even assuming that there are no other reactions but iron dissolution occuring on the anode, amount of carbon dioxide evolving will be only twice larger than the amount of hydrogen evolving. This is not as huge difference in speed as you suggest, and that's only assuming there is no oxygen evolving at the anode at all. There is oxygen evolving and anode corrosion is a slow process, so amount of carbon dioxide evelving should be much, much lower.
That's right - but the point is that being a homogenous reaction it forms much, much smaller bubbles, so while the amount that evolves is much smaller, the fact that the size of the bubbles that form is also much smaller means that you get lots and lots of bubbles - hence the effervescence that is such a widely used qualitative test for carbonates.
IU'm not suggesting that's the only reaction - just that it is a contributor.
Mark Imisides New Member -- Do you have examples of gas or liquid electrodes that are currently being used for this process?
I don't understand your question - what is a "gas or liquid electrode?"
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I still don't feel convinced. No matter what their size is such bubbles are short lived - when they get to the surface, they pop. They don't create a stable foam.
Besides, unless the electrode is highly polished, it is much easier to start bubble creation on the surface, than inside of the solution. That's no different from using boiling chips. No idea why you think homgenous reaction gives many small bubles - quite the contrary, activation energy required to create a bubble is very high in the bulk, so once the bubble is created its grow is favored over new bubble creation. That leads to small number of large bubbles, not large number of small ones. On the rough surface of electrode situation is opposite, nucleation being a key word.
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Is the foam a solid stabilised foam caused by bubbles of hydrogen, oxygen or carbon dioxide stabilised by the insoluble carbonates
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stabilised by the insoluble carbonates
Honestly, you were faster by several hours. Few hours ago I have seen some precipitate on the surface of water I am using to water my plants and something clicked... but I forgot to look for this thread and add a comment.
If that's the case, just using distilled (DI, RO) water should stop foam creation.
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I still don't feel convinced. No matter what their size is such bubbles are short lived - when they get to the surface, they pop. They don't create a stable foam.
Besides, unless the electrode is highly polished, it is much easier to start bubble creation on the surface, than inside of the solution.
Correct - but the size of a bubble is determined by when it stops growing, not how easily it starts growing.