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Author Topic: Why does electricity flow in this experiment?  (Read 11093 times)

Offline sorin cezar

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Why does electricity flow in this experiment?
« on: 29/10/2013 10:21:21 »
A simple circuit consisting in a 1,5 V battery, an electrolytic cell and an ammeter  is built up using simple materials. For electrolytic cell, two graphite electrodes recovered from a pen is the simplest solution.  The experiment performs fine with a single battery, but in case more batteries are used, the arrangement must be in parallel in order to have a potential lower then 1.7 V,  avoiding water electrolysis.
At beginning pure water (distilled or better deionised water) is poured into the electrolytic cell and the electric current in circuit is measured. As far pure water is a poor electric conductor, the experiment starts with a zero intensity indication on the common ammeter scale (there is a small current which can be detected switching the ammeter on micro domain, but this current is irrelevant for the experiment). 
Now a quantity of few grams of reagent grade NaCl is added to the electrolytic cell. Without any agitation, without changing the position of electrodes, an electric current appears in circuit and after about one minute the value indicated is about 9 mA. In other repetitions and using more batteries in parallel the current can arrive to 500 mA.  Of course the value of this current is dependent on a large categories of factors like distance between electrodes, quantity of salt added, geometry of electrodes and cell, agitation, source power, etc. This current can run an indefinite time through circuit if we provide a stabilized source of current; with a common battery, electric current is going to decrease slowly in time (usually hours)  because the battery gets exhausted.
What? Did my instrument really indicate such values?  How is this possible? Why do we have an electric current into circuit?
It is accepted that salt solution permits to electric current to pass through, and this is due to the ions which travel toward electrodes and chemical reactions take place at electrode-solution interface. But what’s happened if the ions have not the possibility to react at electrodes and to change the electrons? From electrochemistry we know that for water electrolysis are necessary more then 1.7 Volts, and for NaCl electrolysis approx. 4 Volts. In our last experiment the voltage is lower than value necessary for electrode reactions and for electron transfer. In this case according to actual physics the ions must migrate to electrodes and at beginning the intensity must be great due to the movement of charges in solution; in short time,  charged regions are formed around electrodes (fig 6.) and intensity of electric current must decrease like in fig 7, admitting a constant velocity of ions in solution. After a short time interval the intensity of electric current must became zero and the solution transforms in a capacitor in this conditions.
The reality is opposite; the current passes through solution a whole night at the same intensity when a stabilized source of current was used.
Of course there was a consume of electricity in this process.
How can we further interpret the Faraday laws of electrolysis? The power dissipated during the night was more then necessary to consume all the liquid in cell, but no volume modification is observed.
You can perform the experiment home using tap water and kitchen NaCl. Of course in this case you will have a background current of about 1 mA, and a boost up when salt is added to the water.
« Last Edit: 01/11/2013 22:20:52 by chris »


 

Offline chiralSPO

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I calculate that 500 mA for 24 hours is enough to electrolyze about 2.0 mL of water, assuming 100% Faradaic yield. I assume your cell was larger than this?

If there really is no reaction going on then you have a capacitor with mobile charges inside. (1g NaCl has about 5.15x1021 Na+ ions and the same for Cl. Each Na+ ion has 1.60x10–19 C of charge (and each Cl has equal but opposite charge). This amounts to a total of 824 C of mobile charge per gram of NaCl (at 500 mA, this would give current for about half an hour per gram of NaCl).

My guess is that there is still an electrochemical reaction going on. My hypothesis is that you are reducing oxygen from the air at the cathode and oxidizing water to oxygen at the anode. Are you able to run the experiment under oxygen-free conditions? (under nitrogen or argon or helium etc.--and make sure to sparge your electrolyte with said gas for 30 minutes before running the experiment. If this results in a closed circuit, then you know the air had something to do with the current.
 

Offline sorin cezar

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Dear chiralspo,
The experiment has the purpose to show a strange situation in electricity and not to increase my bill for electricity.
As far I want to be sure that such effect has indeed place, the electrodes were at  more then 10 cm distance each other, and of course I suppose you know the electric current in this case decrease dramatically in solution.
As far all are fan of quantum tunneling I did not want to get an answer.. it is a particular case ... it can be interpreted with a little bit of attention like a particular situation etc.
Therefore I was interested in the fact that an current is increasing much then an impurity can explain or other default experimental conditions.
Of course it can be arranged to pass a current of few Amps or even bigger and this does not change the conclusion. 

If you do not feel that you are ridiculous with oxygen reactions again and again ... please continue like that...
Maybe in the last 50 years in electrochemistry all wat was achieved was oxigen reactions coming from oxigen dissolved into water ...

At a current of 500 mA, in a normal electrolysis cell with naked eyes you can  see how gases evolves at electrodes...
But probably they becomes soluble in water again ...

« Last Edit: 29/10/2013 13:49:03 by sorin cezar »
 

Offline SimpleEngineer

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I don't get what you are coming from , the salt solution reacts within itself giving the flow of charge, copper doesnt change when you pass electric current through it, why should any other conductor?

It seems your beef with electrochemistry is wild and undirected as now you are just mucking about with saline solution and wondering why nothing happens... nothing happens because there is nothing to happen, things can carry a charge without being affected in any significant way that is what conductance is about. 
 

Offline alancalverd

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Quote
the current passes through solution a whole night at the same intensity when a stabilized source of current was used.

Do you really mean that? A constant current source will increase its output voltage to whatever is required to generate the set current (up to the design limit of the source), so the concentration and dispersal of electrolyte is irrelevant and eventually  the voltage will rise enough to electrolyse the water.
 

Offline sorin cezar

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Do you really mean that? A constant current source will increase its output voltage to whatever is required to generate the set current (up to the design limit of the source), so the concentration and dispersal of electrolyte is irrelevant and eventually  the voltage will rise enough to electrolyse the water.

After this judgement, the voltage of any source increase by itself up to ... what limit...?
In reality if I apply a voltage of 1,5 V on a water solution the voltage cannot be higher then this. There is no water electrolyse in the experiment ...

I don't get what you are coming from , the salt solution reacts within itself giving the flow of charge, copper doesnt change when you pass electric current through it, why should any other conductor?

It seems your beef with electrochemistry is wild and undirected as now you are just mucking about with saline solution and wondering why nothing happens... nothing happens because there is nothing to happen, things can carry a charge without being affected in any significant way that is what conductance is about. 

Your english is too abstract for a common reader... therefore I will explain you the situation in clearer ideas...
The salt solution react within itself? With whom?
In water salts undergo only dissociation and not chemical reaction ...
There is no copper in the experiment .. so please read it again ...

The idea of experiment is:

Have you ever asked what is happen when an electric current is applied to an electrolytic cell and no reactions take place at electrodes?
Have you ever asked why and how an electric current passes through a solution in such conditions?

 

Offline SimpleEngineer

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OK I will repeat hopefully in plainer english.

Dissociation IS a chemical reaction.. trying to argue its not is quite simply ludicrous and shows VERY little understanding of even the very basics of chemistry.

I compared the salty water (conductor) to copper (conductor) to show that just because something conducts a current it doesn't necessarily change.

For me you are incredibly confused about the experiments regarding the GENERATION of current to the CONDUCTANCE of current. During generation the electrodes will change due to the energy 'generated' through the chemical reactions, during conductance there are typically local changes, but the entire is unaffected overtime. The act of hydrolysis is NOT part of conductance, It is the use of the current to break the bonds of water molecules. (think of it like burning an infinite fuse out, you can run x amount of current through it until it begins to melt, keep applying the current and it keeps melting.. reduce the current and it stops melting)

I dont know how much simpler to put it.. and the answer to your two questions..

1. Either it does electrolyse or it doesnt (a fuse either melts or doesnt) a quick look on wikipedia states exactly this
"An electrolytic cell has three component parts: an electrolyte and two electrodes (a cathode and an anode). The electrolyte is usually a solution of water or other solvents in which ions are dissolved. Molten salts such as sodium chloride are also electrolytes. When driven by an external voltage applied to the electrodes, the electrolyte provides ions that flow to and from the electrodes, where charge-transferring (also called faradaic or redox) reactions can take place. Only for an external electrical potential (i.e. voltage) of correct polarity and sufficient magnitude can an electrolytic cell decompose a normally stable, or inert chemical compound in the solution. The electrical energy provided undoes the effect of spontaneous chemical reactions."

2. The solution is a conductor.. have you ever asked how electricity goes through other conductors? again from wikipedia
"In metals such as copper or aluminum, the movable charged particles are electrons. Positive charges may also be mobile, such as the cationic electrolyte(s) of a battery, or the mobile protons of the proton conductor of a fuel cell." The movable charged particle sin this case are the dissociated ions.

and btw if you do try to perform electrolysis on salty water be prepared for more than you expect (2 NaCl(aq) + 2 H2O(l) → 2 NaOH(aq) + H2(g) + Cl2(g))
 

Offline Bored chemist

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OK, this thread is wrong from the start.
This
" the arrangement must be in parallel in order to have a potential lower then 1.7 V,  avoiding water electrolysis. "
shows a lack of understanding of electrode potentials.
Water will be electrolysed at lower voltages.
And this proves it
 "(there is a small current which can be detected switching the ammeter on micro domain, but this current is irrelevant for the experiment).  "

Al this
"From electrochemistry we know that for water electrolysis are necessary more then 1.7 Volts, and for NaCl electrolysis approx. 4 Volts." is also simply wrong, it's the sort of thing that's written by someone who repeatedly refuses to accept that he needs to learn.

" After a short time interval the intensity of electric current must became zero and the solution transforms in a capacitor in this conditions."
Actually, it's as likely to have turned into a cell as a capacitor.
Go and learn some electrochemistry and come back when you have learned there's nothing special about 1.7 volts.
 

Offline sorin cezar

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OK I will repeat hopefully in plainer english.

Dissociation IS a chemical reaction.. trying to argue its not is quite simply ludicrous and shows VERY little understanding of even the very basics of chemistry.


2. The solution is a conductor.. have you ever asked how electricity goes through other conductors? again from wikipedia
"In metals such as copper or aluminum, the movable charged particles are electrons. Positive charges may also be mobile, such as the cationic electrolyte(s) of a battery, or the mobile protons of the proton conductor of a fuel cell." The movable charged particle sin this case are the dissociated ions.

and btw if you do try to perform electrolysis on salty water be prepared for more than you expect (2 NaCl(aq) + 2 H2O(l) → 2 NaOH(aq) + H2(g) + Cl2(g))


Can you present me what new compunds are obtained in a reaction of  disssociation?
A chemical reaction supposes new species are formed... in a dissociation process the ions are surrounded by water molecules and nothings more.

I do not see the relevance of the entire post for the experiement preformed. Can you answer in simple words which is more convenient for you:

A current must not pass through a solution at potential lower then elctrode reaction  and in this case the up experiment prove this is possible

A current can pass through a solution at potential lower then eelctrode reactions and in this case we consume electricity and no processes take place at electrodes; in this case we have to visit again the faradays laws.
Your posting explanation from wiki, does not works for  this experiment ... because the potential difference applied to the elctrolytic cell is lower then necessary for water ot NaCl electrolysis.


OK, this thread is wrong from the start.
This
" the arrangement must be in parallel in order to have a potential lower then 1.7 V,  avoiding water electrolysis. "
shows a lack of understanding of electrode potentials.
Water will be electrolysed at lower voltages.
And this proves it
 "(there is a small current which can be detected switching the ammeter on micro domain, but this current is irrelevant for the experiment).  "

Al this
"From electrochemistry we know that for water electrolysis are necessary more then 1.7 Volts, and for NaCl electrolysis approx. 4 Volts." is also simply wrong, it's the sort of thing that's written by someone who repeatedly refuses to accept that he needs to learn.

" After a short time interval the intensity of electric current must became zero and the solution transforms in a capacitor in this conditions."
Actually, it's as likely to have turned into a cell as a capacitor.
Go and learn some electrochemistry and come back when you have learned there's nothing special about 1.7 volts.

The explanation is very clear and it is in conformity with all accepted manuals of physics...When I have more batteries in parallel, the voltage is the same like for a single battery and intensity of electric current is the sum of individual currents given by each battery...
Therefore in our case there will be a voltage of 1,5 V ... and an increasing current as more bateries are added to the circuit ....

Water is not electrolised at lower then 1,7 potential  difference ...
The  topic of background current and water electrolysis is not the subject of the post... and I will come back with another subject about this fact ...
The topic is how do an electric current pass through a solution when charges are not allowed to discharge at electrodes.

 
« Last Edit: 31/10/2013 12:02:30 by sorin cezar »
 

Offline SimpleEngineer

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Okay from EUPAC definition of chemical reaction
"A process that results in the interconversion of chemical species. Chemical reactions may be elementary reactions or stepwise reactions (It should be noted that this definition includes experimentally observable interconversions of conformers.) Detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. 'microscopic chemical events')."

The chemical reactions involved in dissociation of NaCl in H2O are:

NaCl <=> Na+ + Cl-
H2O <=> H+  + OH-
Na+ + OH- <=> NaOH
Cl- + H+ <=> HCl
NaOH + HCl <=> H2O + NaCl

The presence of the ions floating all around mean there are mobile charge particles willing to carry charge. REGARDLESS of any interpretation of the hydrolysis of water.. most metals carry charge and don't electrolyse.. so why would something NEED to undergo a direct forced reaction to be conductive?

You are really getting messed up over the hydrolysis and conductance.. 1.7V might be what it takes to hydrolyse water but water will conduct electricity at any p.d.

You may as well put fingers in plug sockets and say "I don't conduct electricity unless the volts are above what it takes to kill me" (don't pick out that its amps that kill, because that IS the essence of what YOU are saying)

 

Offline sorin cezar

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Dear simple engineer,
When you want to give me lessons of chemistry please go to the essence and not to what you like to interprete...
When sodium chloride dissolves in water there is no proper reaction because there is no process of interconversion of ,,chemical species”.
Both substances remain in quite the same states (of course there is a interaction between them in solution).
Sodium is present as cation in solid cristal and also in solution. Chlorine is present as anion both in cristal and solution. So... the fact you ommited, with or without intention, to write the charges for the solid NaCl .... does not mean they are reacting...
Please stop writing nonsens like NaOH ...HCl

But, by a physical process (like simple evaporation, or for those who work gentler a under vaccum freezing evaporation,) I can take out the water out  from ssolution... and I remain with solid NaCl as initial .
This means putting sodium chloride into water is a ,,physical process” and not a chemical one ...
When after putting NaCl into water you will be able to recover another ,,chemical species” then I will be the first  to recognise I am wrong.
For the moment none was able to do such thing. I do not comment what is happen in solution ....because  we suppose only ...

I repeat again ... the topic of the experiment ...
If an electric current pass through a solution and no reaction take place at electrodes, it means the electrolysis laws are overrulled ...
It is not worth to give you the references related to the quantity of electricity passing through solution and the mass of substance transformed at electrodes.
On the other hand, if you admit that reaction takes place at electrodes at those potential (1,5 V), and therefore there is an increase for the electric current in circuit,  it means at least the electrochemical series of reduction and oxidation need to be changed...
Again choose what is more pleasent for you ... both means something is wrong in what is written in the books ..
 
I did not get messed up with anything... NaCl added to water increase the conductibility, increase the so called ionic strength, increase the ability of the solution to carry an current .. etc

I am sorry but as far I live on the continent I do not have the ,,ability to taste your british  houmor ..”...


 
 

Offline Bored chemist

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Why do you say "Water is not electrolised at lower then 1,7 potential  difference ..."
when even your own experiments show clearly that it is?

Re.
"If an electric current pass through a solution and no reaction take place at electrodes, it means the electrolysis laws are overrulled"
What evidence do you have that no reaction takes place?

Go and learn some electrochemistry and come back when you have learned there's nothing special about 1.7 volts.
 

Offline SimpleEngineer

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Dear simple engineer,
When you want to give me lessons of chemistry please go to the essence and not to what you like to interprete...
When sodium chloride dissolves in water there is no proper reaction because there is no process of interconversion of ,,chemical species”.
Both substances remain in quite the same states (of course there is a interaction between them in solution).
Sodium is present as cation in solid cristal and also in solution. Chlorine is present as anion both in cristal and solution. So... the fact you ommited, with or without intention, to write the charges for the solid NaCl .... does not mean they are reacting...
Please stop writing nonsens like NaOH ...HCl

But, by a physical process (like simple evaporation, or for those who work gentler a under vaccum freezing evaporation,) I can take out the water out  from ssolution... and I remain with solid NaCl as initial .
This means putting sodium chloride into water is a ,,physical process” and not a chemical one ...
When after putting NaCl into water you will be able to recover another ,,chemical species” then I will be the first  to recognise I am wrong.
For the moment none was able to do such thing. I do not comment what is happen in solution ....because  we suppose only ...

I repeat again ... the topic of the experiment ...
If an electric current pass through a solution and no reaction take place at electrodes, it means the electrolysis laws are overrulled ...
It is not worth to give you the references related to the quantity of electricity passing through solution and the mass of substance transformed at electrodes.
On the other hand, if you admit that reaction takes place at electrodes at those potential (1,5 V), and therefore there is an increase for the electric current in circuit,  it means at least the electrochemical series of reduction and oxidation need to be changed...
Again choose what is more pleasent for you ... both means something is wrong in what is written in the books ..
 
I did not get messed up with anything... NaCl added to water increase the conductibility, increase the so called ionic strength, increase the ability of the solution to carry an current .. etc

I am sorry but as far I live on the continent I do not have the ,,ability to taste your british  houmor ..”...

I really think you need to back to school, you have no understanding of chemistry, you have no understanding of electrical systems at all, you don't even recognise the FACT of dissociation in solutions. If what you said were true, us engineers would have a very very simple time of things, salt water wouldn't corrode stainless steel, boilers would be able to boil salt water etc.

I quoted (mostly) reversible reactions, all of which happen in a saline solution, equilibrium points exist for all of them. Yet even at equilibrium there is STILL reactions going on at set rates (which equal each other). Take a 5 minute glance at any reaction engineering course book and it may enlighten you. (and the boiling off the water thing is either a poor joke or shows how truly ignorant you are)

a quote from wikipedia again

"If a water-soluble electrolyte is added, the conductivity of the water rises considerably. The electrolyte disassociates into cations and anions; the anions rush towards the anode and neutralize the buildup of positively charged H+ there; similarly, the cations rush towards the cathode and neutralize the buildup of negatively charged OH− there. This allows the continued flow of electricity"

This states that the conductivity of the water will inhibit the electrolysis reaction. I don't even have to go to detailed scholarly sources to prove you are ignorant of even the basic premises.
 

Offline sorin cezar

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Re: Why does electricity flow in this experiment?
« Reply #13 on: 05/11/2013 10:34:05 »
Give me a single case where NaCl added to water generate NaOH and HCl...

The quote from wikipedia express a reality and I do not contest this reality ... adding NaCl to water increase solution conductibility ....
But this does not explain the experiment ..... at a potential lower then that necessary for electrode reaction, there should be no increase in the current flowing through solution.
Electrons are not jumping from an electrode to another... and ions do not react at electrodes...
This is what I am pointing out ... 
 

Offline SimpleEngineer

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Re: Why does electricity flow in this experiment?
« Reply #14 on: 05/11/2013 11:32:48 »
Every case.. Think of the reversible reaction.. what happens if you put NaOH and HCl together? (I would suggest doing it aqueously)

You still dont get conductivity.. think of the conductor (salty water) being like any other conductor (copper wire) and you may grasp a little understanding.. Its not fully truthful, but its close enough to begin learning with.

 
 

Offline sorin cezar

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Re: Why does electricity flow in this experiment?
« Reply #15 on: 03/12/2013 09:50:09 »
Every case.. Think of the reversible reaction.. what happens if you put NaOH and HCl together? (I would suggest doing it aqueously)

You still dont get conductivity.. think of the conductor (salty water) being like any other conductor (copper wire) and you may grasp a little understanding.. Its not fully truthful, but its close enough to begin learning with.
 
What a care from an enginner toward a chemist.....

Your suggestion has nothing to do with the experiment. The fact NaOH react with HCl and give NaCl and water does not mean you get the same compounds when you put NaCl In water. This is well known from low level chemistry ...
And imagine you eat NaCl and this salt becomes part of your celular body fluid...

 

Offline chiralSPO

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Re: Why does electricity flow in this experiment?
« Reply #16 on: 04/11/2014 15:21:58 »
The thermodynamic potential at which water will be split into hydrogen and oxygen is 1.229 V (I don't know where 1.7 came from). Usually one must apply a slightly greater voltage to overcome inefficiencies, but with steel electrodes in a solution of sodium hydroxide there is definitely measurable current at 1.6 V.

As to whether dissolution is a physical or chemical transformation is somewhat of a matter of semantics. However, I would whole-heartedly argue that it is a chemical reaction (though I would also argue that the "simple physical" transformations are also chemical, and not so simple)

Dear simple engineer,
When you want to give me lessons of chemistry please go to the essence and not to what you like to interprete...
When sodium chloride dissolves in water there is no proper reaction because there is no process of interconversion of ,,chemical species”.
Both substances remain in quite the same states (of course there is a interaction between them in solution).
Sodium is present as cation in solid cristal and also in solution. Chlorine is present as anion both in cristal and solution. So... the fact you ommited, with or without intention, to write the charges for the solid NaCl .... does not mean they are reacting...
Please stop writing nonsens like NaOH ...HCl

But, by a physical process (like simple evaporation, or for those who work gentler a under vaccum freezing evaporation,) I can take out the water out  from ssolution... and I remain with solid NaCl as initial .
This means putting sodium chloride into water is a ,,physical process” and not a chemical one ...
When after putting NaCl into water you will be able to recover another ,,chemical species” then I will be the first  to recognise I am wrong.
For the moment none was able to do such thing. I do not comment what is happen in solution ....because  we suppose only ...

The fact that the sodium retains it's cationic nature in solution, and that NaCl can be recovered afterwards is not enough to say that the dissolution is not a chemical reaction. We can use infrared spectroscopy to observe the structure of water and solutions of things in water--there is definitely a change in this structure when NaCl is added.
 

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Re: Why does electricity flow in this experiment?
« Reply #16 on: 04/11/2014 15:21:58 »

 

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