Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: Nick Meyer on 09/06/2006 18:03:01
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I am watching a 13.8v at 4-6Amp power supply is this good for electralysis? How about 13.8 at 3Amps?
Thanks for the help guys[8D]
Nick
If its not illegal... It's legal!
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Please help me!!!!!!!!!!!!
Nick
If its not illegal... It's legal!
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I would... but im not well educated in that area yet... sorry
Post it in a forum at you might have to be patient.
you could also google it.
E=MC2... m=deg/360 X C... C= PiD
therefore E=deg/360 X 2(PiD)
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What are you electrolyzing? It depends on how much and what compounds you are electrolizing. The amperage only governs how fast the reaction takes place, but the voltage governs what you can electrolize. If you're using pretty standard materials (you're not trying to oxidize gold I hope) then around 3 V should be enough. The standard oxidation potential for Au --> Au+ + e- isn't even on my chart. I'd imagine you need quite a bit of voltage for that.
"His mind is the ultimate weapon!"-MacGyver television series
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Is it bad to have higher voltage?
Nick
If its not illegal... It's legal!
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quote:
Originally posted by Nick Meyer
Is it bad to have higher voltage?
quote:
The immense variety of reactions that one can perform via electrolysis makes it a useful tool not only for classroom demonstrations, but also in countless types of industry.
In electrolysis, the anode is the positive electrode, meaning it has a deficit of electrons; species in contact with the anode can be stripped of electrons (i.e., they are oxidized). The cathode is the negative electrode, meaning it has a surplus of electrons. Species in contact with the cathode tend to gain electrons (i.e., they are reduced).
A higher current flow (amperage) through the cell means it will be passing more electrons through it at any given time. This means a faster rate of reduction at the cathode and a faster rate of oxidation at the anode. This corresponds to a greater number of moles of product. The amount of current that passes depends on the conductance of the electrodes and electrolyte, though it also depends on how much current the power source itself can generate.
Current also makes a difference in that it can shift chemical equilibria by sheer mass action. The processes in an electrolytic cell with just two or three reactants can become very, very complex. Most of the time it's best to search the literature to see what current density works best for a desired process. For instance, metals plated at a certain current density might form a durable and shiny coating on the substrate, while some other current density might form an excessively grainy, dull coating.
A higher potential difference (voltage) applied to the cell means the cathode will have more energy to bring about reduction, and the anode will have more energy to bring about oxidation. Higher potential difference enables the electrolytic cell to oxidize and reduce energetically more "difficult" compounds. This can drastically change what products will form in a given experiment. On a practical level, both current and voltage determine what will form in a cell.
So, what happens in an electrochemical cell? In practice, things aren't as simple as one might plan. There can be side reactions. These can become intractably complex unless one has studied electrochemistry for many years. In many cases it becomes a matter of experience -- or exploring the existing literature. Electroplaters, for example, generally know what conditions work best for a given type of plating: current, voltage, electrode material, electrode shape, etc.
When determining what will happen when current passes through the electrolytic cell, five of the most important variables are:
1. Electrode composition
2. Electrolyte composition
3. Voltage and Current levels
4. Temperature of the system
5. Partition, if any (i.e., do the anode and cathode solutions mix freely, or are they separated by a membrane or salt bridge?)
If the electrolyte contains chemical species that will be reduced at the cathode or oxidized at the anode (or both), that means chemical change. The electrolyte can form one or more compounds that weren't in there before.
A given compound could form at one electrode but diffuse back over to the other electrode where it promptly breaks back up into its reactants.
If the electrolyte does not participate in any reaction(s), it will just act as a conductor of electricity. The same goes for the electrodes. Some materials will react but will not produce anything obvious (gases, precipitates, or color changes). Others will not react at all under the specific combinations of voltage and current.
With appropriate metals as the electrodes, electrolysis brings about a very useful process:
The anode is consumed as its metal is oxidized, turning the metal into positive ions which go into solution.
The cathode is plated with freshly-reduced metal ions that come out of solution.
Some metals, such as platinum, don't usually participate in electrolysis reactions, at least not directly. Among other things, this means that the anode will not disintegrate over time, which in turn means the set of electrodes can last years (just don't put them in aqua regia!).
Cautious electrolysis of NaCl solution with the Brownlee apparatus will produce hydrogen plus aqueous NaOCl if the experiment is carried out in a single, unpartitioned jar (such as the one provided) with stirring. What happens first is that hydrogen, chlorine, and NaOH are produced, and the aqueous chlorine and NaOH then react to form NaOCl. Higher temperature tends to produce ClO3- (aq.) instead of OCl- (aq.).
DON'T electrolyse a solution where aqueous Cl2 or Cl- is present with aqueous ammonia or NH4+, unless you know PRECISELY what you are doing. There are a couple different things that could form and poison you, cause an explosion, or both.
Some chlorine will undoubtedly escape the hypochlorite cell and go into the air without being consumed, so this whole operation should be done in a fume hood.
Running the electrodes in two separate partitions will produce chlorine (poisonous!) and hydrogen gases, plus aqueous NaOH.
The odor of chlorine is sharp enough that, if there's a leak, you should have sufficient warning to shut off the voltage and get out of the area before there's any injury. Regardless, use a fume hood if collecting chlorine gas. Use a fume hood if you think there even might be chlorine gas or any other toxic surprises.
Another, similar experiment is the electrolysis of a concentrated NaBr or KBr solution. This will produce hydrogen at the cathode and bromine at the anode. The latter is corrosive and very poisonous. When the bromine reaches saturation in the water, guess where it will go next? Into the air. (This experiment must be performed in a fume hood and with an emergency shower nearby in case of accidents.) Bromine in any appreciable amount will also begin to attack the platinum electrodes (!), so a modified apparatus using graphite electrodes would have to be used.
It can be very dangerous to experiment wantonly with electrolysis of chemical solutions- you may produce an unexpected or even lethal result.
A regulated DC voltage source is preferable to ordinary batteries. Use a supply with built-in current limiting- this is a feature of almost any decent power supply, but double-check just to be safe. You can start the source out at its lowest voltage setting and gradually increase the voltage until a steady, controlled electrolysis reaction is taking place. Electrolysis can force many chemical reactions to go against their "normal" (spontaneous) direction; this will occur when a certain electric potential (i.e., applied voltage) is reached. For example, an electric current can cause Pb++ ions in water to form PbO2 (solid) and H+ (aq.), a reaction which normally proceeds the other way.
Electrolysis of water will begin around a minimum of 1.2 volts and will increase in rate as the voltage is increased. Typically, the electrolysis is carried out around 6 volts. You can slowly increase the voltage as high as 10 or 12 if the reaction is proceeding slowly. That's for water only, with perhaps a bit of H2SO4 electrolyte.
Don't experiment with different voltages using other electrolytes if you don't know what will be produced. Be careful with car batteries or other storage batteries. For these you should build a resistor and a low-amperage fuse into the circuit so it doesn't let too much current flow. A car battery holds a great deal of power and can produce dangerous levels of current. Generally speaking: the higher the ionic strength of a solution, the greater the magnitude of current that can flow.
If the voltage across your cell is 12 volts and you want 2 amperes to flow, the total resistance of the circuit should be 6 ohms. Keep in mind that the resistance of the electrolytic cell often changes as the reaction progresses. For safety and consistency, you'll need a rheostat and a way to monitor the current. A decent lab power supply has both features built in.
Also, it is undesirable to generate gases so quickly that your gas-collection tubes are overflowing. This is especially true if chlorine or other noxious gas is involved. A very popular electrolysis experiment involves measurement of approximate gas volumes and estimation of relative moles of gas produced, so overflowing tubes would spoil the results anyway.
One more caution, even though this may be obvious to the reader: the Brownlee electrolysis apparatus is designed for Direct Current (DC) only! DO NOT attempt to use AC (alternating current) for electrolysis. Because the "cathode" and "anode" are constantly switching places, alternating current produces explosive mixtures of hydrogen and oxygen. Many instructors like to perform combustion experiments with the H2 and O2 in their respective tubes, but a mixture of both gases isn't something to ignite in a glass container...
George