Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: sorin cezar on 24/10/2013 15:47:59
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A simple experiment is proposed below:
The ,,positive” electrode is formed by a Cu piece inserted into a glass of water (or a CuSO4 solution). The ,,negative” electrode is formed by a Zn piece inserted into water or into an acid solution (vinegar, citric or sulfuric acid). Vinegar and citric acid are commonly used in food preparation so it is not a big deal to find them. For a more spectacular visual effect, a solution of sulfuric acid, 3 up to 5M can be used in Zn electrode chamber.
Common tap water can be used. Of course for more elaborated experiments or for the skeptics deionised water is necessary; for home experiments this can be bought from a car shop.
As salt bridge, a covalent compound (graphite) or a metal which does not react with electrolytes (Pt, Au) is used. For graphite, it is possible to arrange a geometrical form in a U shape only from graphite components, or to use two pieces of graphite connected with a metallic conductor. For the simplest setup, two graphite electrodes recovered from used batteries are used. Two graphite pieces recovered from a pen are another available option.
With this set up, an electric current of about 30 μA is counted on the ammeter when in the Zn electrode chamber, water is used. After long time of working, the Zn electrode is consumed, and at Cu electrode no visual modifications are observed.
An electric current of about 50 μA is counted on the ammeter, when in the Zn electrode chamber, vinegar is used as electrolyte. After shorter time of working, the Zn electrode is consumed, and at Cu electrode no visual modifications are observed. Bubbles of hydrogen develop on Zn electrode.
An electric current from 50 μA up to 5 mA is counted on the ammeter, when in the Zn electrode chamber, a sulfuric acid on growing concentration is used as electrolyte.
When sulfuric acid is used, at Zn electrode it can be clearly observed the release of hydrogen gas simultaneously with rapid Zn electrode consume. Formed ZnSO4 gives opalescence in the compartment and starts to sediment when quantity produced is greater then its solubility. At Cu electrode no visual effects are observed.
As can be observed in this simple battery, both ,,oxidation” and ,,reduction” phenomena take place at the same electrode (Zn electrode), and, in the same time, a electric current is counted in external circuit.
Secondary, a non ionic salt bridge is used so again, the ions movement from salt bridge as explanation for charge equilibration does not need any comment.
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[diagram=696_0]
Clever, but unfortunately, your setup is two electrochemical cells connected in series. You have a copper electrode (A) and and graphite electrode (B) in one cell, and another graphite electrode (C) and a zinc electrode (D) in another. Electrons flow from B to C and from D to A. The reduction or oxidation half reactions at each electrode could be:
(A) 2Cu2+ + 4e– --> 2Cu
(B) C + 2H2O --> CO2 + 4H+ + 4e–
(B alt oxidation) 2H2O --> O2 + 4H+ + 4e–
(C) 4H+ +4e– --> 2H2
(D) 2Zn --> 2Zn2+ + 4e–
Do you see gas evolved at either (or both) of the graphite electrodes? Production of CO2 would probably not be observed as bubbles because of its high solubility in water.
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I also want to point out that you are doing some great experiments. Keep it up. Skepticism and experimentalism are the foundation of science. However, you also do have to trust, to some level, the knowledge that has been gained by others using the scientific process. If you think your experiment disproves a belief widely held by the scientific community, understand that it must be held to a higher burden of proof.
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Dear Chiral,
Do you really think that such explanation work?
Even with naked eyes one can see that hydrogen develops on Zn electrode!!!!
Why should electrons make that circulation on and off? Only to fit with your description?
High solubility of Co2 in water ? What are you dreaming... in that container(about 25 ml liquid) I do not think more then few microliters of CO2 are solved in water ...
And the cherise on the tort... graphite do not react in these condition with any of the system component. If this will be the case, you have to propose a new explanation for actual commercial batteries where after few hours the rod of graphite is consumed....
So even for a neofit your explanation is a fake ...
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You certainly have a high opinion of yourself don't you.
"High solubility of Co2 in water ? What are you dreaming... in that container(about 25 ml liquid) I do not think more then few microliters of CO2 are solved in water ..."
Well, that's because you are wrong.
This
http://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html
shows that the solubility of C)2 in water at room temp is about 0.15%w/w
So, your 25 ml of water would dissolve about 0.04 grams of CO2
That's about 20 ml so you are simply wrong by about a factor of a thousand.
Actually, it doesn't matter very much. The oxidation of graphite will take place in alkaline conditions, but in neutral ones the production of oxygen is more likely.
However, rather than being silly, perhaps you should calculate the rate of gas production at 1 mA- how many ml of gas would be produced each minute?
We have covered this "Even with naked eyes one can see that hydrogen develops on Zn electrode!!!!" before - though you didn't understand it. It's called "local action"
"graphite do not react in these condition with any of the system component."
Graphite will react with oxygen, produced at the anode so you are just plain wrong again.
In commercial batteries the gas produced at the graphite electrode would be hydrogen with which it won't react.
You really need to stop this "I am always right" attitude- it makes you look childish.
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Bored chemist,
There is a Spanish saying: Who wants to trick the devil, must wake up early in the morning.
It seems you woke up a little bit late ….
The value of CO2 solubility indicated in the link is true for certain conditions: pure water, degassed water, etc and I agree with that value in specified conditions.
In real word the situation is a little bit different, or at least for the conditions the experiment was performed in …
As far in the experiment there tap water was used, in this water you have already mainly the gases which constitute the atmosphere solved (CO2, O2, N2), besides mineral salts, contaminants etc .
Therefore the value of ,,theoretical CO2” solubility for the water in battery is irrelevant.
This water has already a mixture of gases in it and there is equilibrium between gases in water an atmosphere.
If I come with a bit more gas in water, only the excess added by me will leave the water and not the entire CO2 from water.
Therefore if there is a CO2 generation this have to be observed immediately so I am not wrong with anything.
Beside this if you stick to the chiral explanation, you will see that I do not have Cu2+ in solution, therefore there is no reduction at Cu electrode. Has 25 ml potable water so much copper to maintain an electric current generation?
In potable water by definition the Cu content is less then few mg per L, this means micrograms for the volume of liquid taken into study …
Let us be a bit reasonable ….Chemistry is a science of measurements …..
If you justfy a possible secondary cell for potable water and low intensity current, this is not working for pure water or when sulphuric acid is used in the experiment. It is impossible to atribute a current of 5 mA, as being generated by a inexistent Cu2+
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"There is a Spanish saying: Who wants to trick the devil, must wake up early in the morning."
That's mildly interesting.
But irrelevant.
"It seems you woke up a little bit late …."
No, they changed the clocks to daylight saving time last night so I woke up early.
"In real word the situation is a little bit different" Probably more of a "little bit" than you think.
"As far in the experiment there tap water was used, in this water you have already mainly the gases which constitute the atmosphere solved (CO2, O2, N2),"
Yes, and the atmospheric concentration of CO2 is about 400 ppm, while that concentration at which it will out gas at the solubility limit is about 1000000 ppm.
If you can explain how the presence of a trace of dissolved O2 or N2 in the water will materially affect the solubility of CO2 then I'm interested because the presence of other gases usually doesn't affect the equilibrium solubility more than slightly.
But if you are just making a baseless assertion (and I think you are) then you will look silly (again).
The presence of minerals makes it more interesting because there might be enough of them to make a difference.
In particular, if there are carbonates present in the water (which is quite common) then they will increase the solubility of the CO2 by reaction to form bicarbonate.
So, you are now more than a thousandfold wrong.
"Beside this if you stick to the chiral explanation, you will see that I do not have Cu2+ in solution"
Actually, if you look you will see that the surface of the copper is a bit oxidised and as soon as you put that in water you will dissolve some- not a lot.
What you have is more like the Ag/AgCl electrode or the Sb/ Sb2O3 electrod sometimes used to measure pH where a low but nearly constant concentration of a metal ion is maintained by the presence of a salt or oxide with a fairly low solubility.
But the copper is a bit of a red herring anyway.
There is, as you say, oxygen in the water.
It's likely that a lot of the current is carried by the reduction of dissolved oxygen at the copper electrode.
Perhaps you should have got up a bit earlier and read some electrochemistry.
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A current of 5 mA = 0.005 C/s = 0.0000000518 moles of electrons/second
= 0.55 mg of graphite oxidized per hour at 5 mA
This means that you would have to run this cell for several hours to observe corrosion of the electrode or CO2 bubbles (even if the water CO2 concentration is initially in equilibrium with the atmosphere, it is far from saturated--think how much CO2 remains in "flat" Coca Cola.)
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As far I have enough experience in laboratory work, I will not argue at infinite here about small things...
If you want to repeat the experiment, you ll see that your predictions have nothing to do with the experimental reality.
I made the experiment using platinum recovered from some broken electrodes as bridge and I am sure that nor CO2, nor Cu is involved into the general reaction and in the specified conditions of experiment.
As far I have other in working experiments it is no use to discuss about hypothesis.
I have posted 2 new experiments about chaige displacement and electric curent in physics section.
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So, you didn't understand this bit of what I wrote then.
"There is, as you say, oxygen in the water.
It's likely that a lot of the current is carried by the reduction of dissolved oxygen at the copper electrode."
Face it, you have no real idea what you are talking about.
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Bored chemist,
I think the first think which worth to be detailed are the ,,reactions in the circuit".
If you stick to the reactions presented by chiral :
(A) 2Cu2+ + 4e– --> 2Cu
(B) C + 2H2O --> CO2 + 4H+ + 4e–
(B alt oxidation) 2H2O --> O2 + 4H+ + 4e–
(C) 4H+ +4e– --> 2H2
(D) 2Zn --> 2Zn2+ + 4e–
I do not have Cu2+ into circuit so ...as far the second cell has a wrong semireaction, it is not worth to further detail about the topic.
As far you did not posted a explanation and only advanced ideas... please formulate a bit chemistry ...
After that I will detail why your explanation is or isnt credible ....
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Sorin, perhaps you would like to tell us what you think is going on...
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Dear Chiral,
Now, I am writing the text for a new fundamental effect in nature... in fact it is a new way of generating an electric current.
You may think the time when with a magnet and a conductor Faraday discovered the magnetic induction has passed ... I was thinking the same ...
But sometimes as Edison said..... something is 99 % perspiration and 1 % inspiration ....so I had a bit luck and I found something...
I do not know what are the implication of this thing.. and I have other things to do instead of continuing this line of research ... but I suppose there will be some interesting application in the future ..
So stay tuned....
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By the way ... the experiment is consistent with another simpler experiment made with molten NaCL...
If I melt NaCl and I put a 1,5V battery and a ammeter ... when NaCL melts the current into circuit increases from 0 to 50 mA. Of course again the current is dependent on the distance between electrodes and if you repeat the experiment you can find a different value.....
The problem is none can accept that electrode reaction take place at 1,5 V, when electrolysis of molten NaCL starts at 4,1V.
How the hack an electric current pass through ionic solution?
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"electrolysis of molten NaCL starts at 4,1V"
No it doesn't, and you say you proved it.
You need to understand that there is more to electrolysis than adding electrode potentials.
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Correct me if i am wrong... Graphite (although being covalent) is an electrical conductor...
The answer to your posts question is.. yes.. the salt bridge experiment actually was formed to show how ionic substances conduct electricity without the need for reactions.. and is now used in practice to separate incompatible substances or where the interactions between the substances would create interference with the experiment.
So any conductor would do, as long as it does not react with either of the solutions.
give definate solution and electrode material and we can all take it in turns to tell you what is happening as I am seriously doubting you have the understanding to work it out for yourself.
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Graphite is a conductor (semiconductor to be more precise) and it is acceepted that its conduction is by electrons.
I used this material as salt bridge to show that something is not consistent with how we immagine the charge equilibration for a battery containing such bridge works.
According with what is written in any low level chemistry book such battery (with a semiconductor or metallic bridge) must not work because there is now way to equilibrate the charges...
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I dont know what 'low level' books you have read, but the means of balancing the charges is through the conductor. .. I dont know how to phrase that the system works with the bridge but not without the bridge.
Like the bridge is a switch for the circuit.. if its not there, the circuit is broken and there is no flow so no electrochemistry happening, if it is there then there is flow of charge from one to the other and so the circuit works.
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As with all your other experiments, the chemical reactions between the electrodes and electrolytes are irrelevant. The driving voltage is due to the difference in electronegativity between zinc and copper and the current is the quotient of voltage divided by total circuit resistance.
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"I used this material as salt bridge to show that something is not consistent with how we immagine"
http://en.wikipedia.org/wiki/Royal_we
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Alancalverd in what century have you learned chemistry?
Any commercial cell is powered by a chemical reaction...
In the proposed experiment, where Bored chemist dared to bet his house, there si indeed a new possibility of getting an electric current in absence of a chemical reaction ...
But, you have to supply a mechanical action in order to get an useful current.
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Read what I wrote. The reactions are irrelevant to the cell voltage.
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In the proposed experiment, where Bored chemist dared to bet his house, there si indeed a new possibility of getting an electric current in absence of a chemical reaction ...
But, you have to supply a mechanical action in order to get an useful current.
What proposed experiment?