Electrochemical cell thread

[vrus]

I did a practical in school 2day about electrochemical cells, using a variety of metals and salt solution. I decided to open a thread on how they can be made more efficient, different designs, anamolous finds, etc.

 

I come to understand that the larger the difference between the electrodes, the larger the potential difference/ voltage. So we used a Magnesium strip and a graphite rod, giving a voltmeter reading of 1.4 V. I was surprised, as I didn't know it was this easy...

 

But when I subbed the voltmeter with a filament bulb, there was hardly any effect, except for a very,very, dim glow...

 

I think the reason for this was a very low current. So how to increase current ? Decrease Resistance ? How to decrease resistance ? Use a paralell circuit ? Can someone clarify this ?

 

My teacher also said that the surface area of the electrode in contact with the electrolyte won't affect the voltage. How is this true? I think this should allow more ions to dissolve, resulting in a larger voltage...

 

Would more than one of these cells in series or paralell give a better result ?

What would be an ideal electrolyte commonly available at home other than aqueous sodium chloride ?

[YT2095]

have you seen this thread also?

 

http://www.scienceforums.net/forums/showthread.php?t=2863

 

might be worth a read for a few ideas

[jdurg]

Remember that in electricity there is a lot more than volts that you need to remember. A good analogy is that voltage is a measure of how far something will fall. A high voltage is like having an object high up on a shelf falling down to the ground, while a low voltage is like having the same object fall from a much lower shelf.

 

The amperage defines how many 'objects' are 'falling' across that voltage. If you have very low amps, it's like you have a very tiny object falling down. If it falls from a high enough level (has a high enough voltage), even the small objects can cause some harm. A high amperage is like having a MASSIVE object falling down. With a high amperage, you don't need a lot of volts (room to fall) in order to cause harm.

 

The power of something is the combination of the voltage and amperage of a circuit. If you have a 60 watt light bulb being used and you're running on a 110 Volt line, you're using 60/110 = 0.545 amps.

 

When you put a light bulb into your electrolytic cell, you're putting across aproximately 1.4 volts, though the real number is far less. In order to light the lightbulb up to it's maximum capacity (assuming you're using a 60 watt bulb), your circuit would need to generate 42.9 amps! That's not going to happen. As a result, your bulb will seem quite dim.

 

The whole volts times amps equation is also why we don't get hurt from static electricity. Static Electricity is on the order of many, many, many thousands of volts. The amperage, however, is almost nothing so when we get a shock it's just annoying and not deadly. On the other hand, an electrical socket in your wall only has about 110 or 120 volts in it, but a LOT more amperage. Therefore, putting your finger in a socket can cause serious injuries. A 1 amp 'jolt' at 100 volts is the same strength as a 0.01 amp 'jolt' at 10,000 volts.

[YT2095]

a good peice of "test kit" for experimenting with such home-made cells, are these cheap digital watches or calculators that use watch batteries, there are "Water Powered" items such as these for sale too, although the term water powered isn`t strictly accurate, and it`s down to a large Zinc electrode that corrodes away over time (about 3 years or so) it serves as a good demonstration how you can get something Usefull out of your cell

[vrus]

I encounetered a problem recently. I used a strong salt solution and magnesium and graphite as electrodes and got the faint glow with the same bulb described before. But then I used Aluminium instead of magnesium and nothing happened. I was expecting it to get brighter, as the difference in reactivity is made larger. Is this because of the Al's oxide layer ?

 

I then used a solution of salt, vinegar and some bleach with the same electrodes. But neither worked. Even my LED didn't light up! So I split the volume to make two cells; one with Al and graphite and the Mg and Cu. Still no result...

 

Can someone provide an explanation as to why this is not working and a solution to it ? Great;y appreciate any help in these difficult days !

 

(That was my 100th post !!!)

[woelen]

Aluminium metal actually is useless as electrode material. The oxide layer prohibits acceptable currents.

 

Your potential may be high, but you have a huge internal resistance in your 'cell'. As soon as you connect a load to the cell, the voltage drops, due to the high internal resistance. Oxidizing solutions do not help you with this. Strongly acidic solutions (like HCl) may help somewhat, but these quickly dissolve the aluminium after an initial transient. I would suggest you to take zinc metal instead.

[vrus]

Thnx for that Woelen, but what should I use with Zinc, i.e as the other electrode ? Can vinegar substitute for Hcl, as I'm sure I mentioned this somewhere before, it is impossible to obtain any chemical supplies here...

[YT2095]

Aluminium metal actually is useless as electrode material. The oxide layer prohibits acceptable currents.

 

True for Some electrolytes yes, but an Alkaline electrolyte such as KOH or NaOH has no problem with it at all, I`ve used quite a bit of it in the past and never encountered a problem

[woelen]

Aluminium can be used for electrolysis, but it is not very useful as an electrode for producing a current in a cell. What vrus attempts to do is not electrolysis, but make a cell, which produces some current.

 

@vrus: Your electrolyte must have sufficient conductivity. Vinegar only is a weak acid and hardly conducts electricity. The internal resistance of your cell will become very large and make it useless.

 

Can't you even get dilute HCl? If you can get that, then you can make a nice cell as follows:

 

• Dissolve as much as possible of zinc metal in HCl. As a substitute you may simply try a solution of NaCl instead of zinc, dissolved in HCl. That is even more simple and also will do.
  
• Dissolve as much as possible of copper metal in a HCl/H2O2 mix. Heat the mix for some time to get rid of excess HCl and H2O2.
  
• Put both solutions in separate beakers.
  
• Take a flexible tube, fill this with concentrated salt-water and close both ends with cotton-wool (which will be soaked with the salt-solutions). Immerse one end in the beaker with copper-solution and immerse the other end in the beaker with zinc solution.
  
• Dip a copper plate in the copper solution and dip a zinc plate in the zinc solution. Between the copper and zinc plates you will have a voltage with low internal resistance and that makes your cell nicely powerful.
  

 

Try to go to a hardware store and see if you can find 10% HCl. I hardly can imagine that even such dilute acid cannot be obtained. A solution with 3 to 10% H2O2 should also be available.

 

Easy to obtain chemicals might be copper sulfate and zinc oxide for you. They are available at pottery and ceramics stores. With these at hand your copper half-cell can simply be made by dissolving the copper-salt in water. The ZnO can easily be dissolved in dil. HCl.

As an alternative for HCl you could try to find dilute H2SO4 as the acid in car batteries. With some luck you can obtain that at auto parts suppliers. Yet another nice alternative for HCl is NaHSO4, which is present in many toilet cleaners and also available as pH-minus for swimming pools. You should be capable to find one of these chems as your acid.

[YT2095]

alu and copper in a NaOH electrolyte will give enough power to light an LED, I`ve done it.

Magnalium works equaly well also.

[woelen]

alu and copper in a NaOH electrolyte will give enough power to light an LED' date=' I`ve done it.

Magnalium works equaly well also.[/quote']

I'm never too old to learn .

 

So, if I understand well, what you did is take a single beaker with NaOH-solution, a copper plate and an aluminium plate and you connect a LED between the two plates?

 

This is a nice experiment to try. What do you get at the copper in this case? I assume the aluminium slowly dissolves, forming aluminate, but do you get hydrogen at the copper plate?

 

Al --> Al(3+) + 3e

 

The electrons flow to the copper electrode. Over there, what do these electrons do? I do not understand, because there is nothing which can accept these electrons, besides the water, which then would form hydroxide and hydrogen gas. Howver, if that is the reaction, then I see no reason why not any other metal would do equally well and I see no reason why electrons would flow .

 

The cell I know, has copper ions around the copper plate and what you see then is that at the copper plate, more copper is plated out of solution:

 

Cu(2+) + 2e --> Cu

 

In that case, the reaction can be perfectly understood, because there is a driving force for electropositive aluminium or zinc to dissolve and the more noble copper to plate out.

[YT2095]

actualy the copper I used in my cell remained unaffected, only the Alu corroded over time (giving off Hydrogen bubbles). I used a fairly weak soln of NaOH too, too strong and your alu doesn`t last 5 minutes and the whole lot gets quite hot.

 

in post #2 the link there will show pictures of my cell(s) working, amgnallium was used in this instance, but I`ve done the same with plain Alu and it worked just as well

I considered using Iron in place of the copper also, I`ve not yet got around to testing this though.

and interesting effect with Iron and Alu as electrodes is that they change polarity depending on the PH of the electrolyte too

 

edit: actualy, Why don`t You have a go at this challenge too, you`de be great at it I`m sure

[vrus]

Aluminium can be used for electrolysis' date=' but it is not very useful as an electrode for producing a current in a cell. What vrus attempts to do is not electrolysis, but make a cell, which produces some current.

 

@vrus: Your electrolyte must have sufficient conductivity. Vinegar only is a weak acid and hardly conducts electricity. The internal resistance of your cell will become very large and make it useless.

 

Can't you even get dilute HCl? If you can get that, then you can make a nice cell as follows:

 

[list']

[*]Dissolve as much as possible of zinc metal in HCl. As a substitute you may simply try a solution of NaCl instead of zinc, dissolved in HCl. That is even more simple and also will do.

[*]Dissolve as much as possible of copper metal in a HCl/H2O2 mix. Heat the mix for some time to get rid of excess HCl and H2O2.

[*]Put both solutions in separate beakers.

[*]Take a flexible tube, fill this with concentrated salt-water and close both ends with cotton-wool (which will be soaked with the salt-solutions). Immerse one end in the beaker with copper-solution and immerse the other end in the beaker with zinc solution.

[*]Dip a copper plate in the copper solution and dip a zinc plate in the zinc solution. Between the copper and zinc plates you will have a voltage with low internal resistance and that makes your cell nicely powerful.

 

Try to go to a hardware store and see if you can find 10% HCl. I hardly can imagine that even such dilute acid cannot be obtained. A solution with 3 to 10% H2O2 should also be available.

 

Easy to obtain chemicals might be copper sulfate and zinc oxide for you. They are available at pottery and ceramics stores. With these at hand your copper half-cell can simply be made by dissolving the copper-salt in water. The ZnO can easily be dissolved in dil. HCl.

As an alternative for HCl you could try to find dilute H2SO4 as the acid in car batteries. With some luck you can obtain that at auto parts suppliers. Yet another nice alternative for HCl is NaHSO4, which is present in many toilet cleaners and also available as pH-minus for swimming pools. You should be capable to find one of these chems as your acid.

 

 

Can I use Na2CO3 instead of NaOH ? Oh and yeah I can get H2O2 @ 6%

 

I'll check for HCl again...

[YT2095]

sodium carbonate won`t work, it has to be the hydroxide.

[jdurg]

HCl can be found in a grocery store if you look at the right place. Many of these Calcium/Lime/Rust removers contain a great deal of HCl in there. If you really want to concentrate it, just heat the CLR so that the HCl is driven off and make sure you direct the hydrogen chloride gas into another container of distilled water. You should be able to make some very concentrated HCl if you have enough of the CLR. Also, you can go to a pool chemicals store and get HCl in something upwards of a 10-gallon container.

[YT2095]

or a Brick and Masonary yard, they sell Brick cleaner 30% HCl(aq) 5 litres for about £3. that`s where I got mine from

[woelen]

Jdurg and YT, this is very true for you, but I'm afraid vrus is in a country, where things are totally different. It really is remarkable, how difficult it can be to find even the most basic chemicals in certain parts of the world.

[vrus]

YT and jdurg, in case you're killing urself with curiosity as to which country this is ..... I live in Kuwait.

But don't worry, im not kuwaiti...