Hi,
i recently constructed a hofmann apparatus at home out of pvc and had some trouble with it. Basically, once it is set up, i only get gas from one electrode, the other does nothing. H2SO4 is used as the electrolyte, and the is 12 volts at 4 amps being put through it, DC. are there any simple flaws i am over looking as i just want to keep the oxygen and hydrogen separate.
thanks, your help is greatly appreciated.
http://en.wikipedia.org/wiki/Hofmann_voltameter
As I interpret the above reference, a Hoffman apparatus requires platinum electrodes if it is to generate hydrogen. Otherwise metal from one electrode will plate on the other.
Are you using platinum electrodes?
no, both electrodes are made of copper and the electrodes shouldn't matter, as long as they conduct
I stand by my previous answer. See
http://www.qsinano.com/news/releases/2006_06_08.php
There are acceptable substitutes for platinum in H2O electrolysis to produce H2, but copper is not one of them.
You can successfully use mechanical pencil leads as electrodes in a demonstration apparatus, but the clay/carbon "lead" is not a good conductor and the amount of gas produced is not high.
would you be able to explain why for me?
why can't copper be used? why does this result in none of one the gases being given off?
The metal composition of the electrodes doesn't matter as far as generating H2 and O2 gases initially. However, it is desirable for the composition of the two electrodes to remain constant so that their performance will not change during electrolysis. Platinum works very well but it is expensive.
If the water is made conductive by adding a little sulfuric acid, H2SO4, lead electrodes (yes, LEAD) would work well for a while. An even better cheap choice is lead solder wire. A copper anode would dissolve gradually forming a copper salt in solution.
Just to add my 2 cent's worth:
You also could use graphite or carbon rods such as those from old worn out flashlight cells, specifically such as those that come from D or C cells. The why it won't work, at the anode, it is easier for Cu to go into solution (Cu ==> Cu+2 + 2e for which Eo = -.34 volts than it is to oxidize water
2H2O ==> O2 + 4H^+ + 4e for which Eo = -1.23 volts. Of course using Eo means 1 M solutions an all that stuff and there is overvoltage to consider. In the real world you probably get some of several reactions going on at the same time or at least in short sequences, as GK as suggested,
thanks, that pointed it all out
Hi there! I would be happy to help you troubleshoot your Hofmann apparatus. It sounds like you're experiencing an issue where only one electrode is producing gas while the other one is not. There could be a few reasons for this, so let's go through some of the most common ones:
1. Electrode placement and orientation: Make sure that the electrodes are properly placed within the electrolyte solution. The gas-producing electrode (cathode) should be positioned near the hydrogen outlet, and the non-gas producing electrode (anode) should be positioned away from it.
2. Electrode material: Check that both electrodes are made of suitable materials for the experiment. In the case of electrolysis, typically platinum or graphite electrodes are used due to their stability and resistance to corrosion.
3. Electrode size: Ensure that both electrodes are of similar size and surface area. If one electrode is significantly larger, it can cause an imbalance in the current distribution and result in only one electrode producing gas.
4. Electrolyte concentration: Check the concentration of your H2SO4 electrolyte solution. If it is too dilute, there may not be enough ions present to support gas production at both electrodes. Try increasing the concentration slightly, but be cautious not to exceed safe limits.
5. Electrolyte level: Make sure that the electrolyte solution covers both electrodes completely. If the level is too low, it may not allow for sufficient contact between the electrodes and the electrolyte, leading to inadequate gas production.
6. Power supply issues: Verify that the power supply is functioning correctly. Check the connections, wires, and ensure that the voltage and current settings are suitable for your experiment. Additionally, double-check the polarity (positive and negative terminals) of the power supply to ensure it is connected correctly to the electrodes.
By considering these potential issues, you should be able to identify and resolve the problem with your Hofmann apparatus. If you have followed these steps and are still facing difficulties, please provide more details so that I can assist you further.