electrolysis

[brianmay27]

ok i can guess that this will be answered in a few seconts . But for years i have tryed electrolysis with water but all i ot was little bubbles. i think it is the source i use. i use a 9 V battery. What voltage and amprage should be ok to get max h2 and o2 production. Thx

[YT2095]

ordinary water doesn`t conduct electricity doesn`t conduct electricity very well, in fact pure water doesn`t conduct at all.

you need a few ions in there to get it going, sulphuric acid is usualy the most common electrolyte used.

[woelen]

You also need a good set of electrodes. The anode must be a graphite rod. Metal wires dissolve and are corroded very quickly.

 

The power supply must be a decent power supply, capable of delivering several amperes of current. A small 9V battery is totally useless.

 

The voltage to be used should not be too high, unless you use a set of resistors to limit the current. A very good method is using a modified PC power supply, with a set of resistors for current limiting.

 

http://woelen.scheikunde.net/science/chem/misc/psu.html

[John Cuthber]

"ordinary water doesn`t conduct electricity doesn`t conduct electricity very well, in fact pure water doesn`t conduct at all."

Oh yes it does. The H+ and OH- generated by self ionisation mean that it has a lagre but finite resistivity. This depends on temerpature but near room temp it's about 20MOhm cm

 

The rate of production of H2 and O2 depends solely on the current. Once you have a high enough voltage to decompose the water, raising the voltage just reduces efficiency and generates waste heat. On the other hand, to get more current you need to raise the voltage or get bigger electrodes, put them closer together and make sure the material between them is a good conductor (like dilute acid rather than water).

[YT2095]

so if his electrodes are 1 inch appart (and probably were) he`d need 50 million volts just to draw 1 amp!

 

he`s using a 9V rail, I don`t think ANY of that comes into it do you?

[woelen]

Theoretically I have to agree with John. Even distilled water conducts some current (it self ionizes a little to hydrated OH(-) and hydrated H(+), the product of the concentration of these ions being 10^(-14) mol2/l2 under standard conditions).

 

Practically, however, that conductivity is very low and with voltages of 9 V, IIRC the current will be in the order of microamperes.

[brianmay27]

Thanks. looked at the site Looks just like i need (since i have 2 extra power supplys). I have a question. where can i find a graphite rod? i heard somewhere that 9v batterys have it but where would you think

[woelen]

The 9V batteries are useless for this. You need a BIG battery, with good electrodes. Use a lantern battery, 6 V, type 4R25.

 

 

Be careful to select a zinc/carbon type. This type of batteries has 4 beautiful large rods in it. It is quite a mess, however, to remove them, but it is worth the effort. These batteries also are cheap, around $5, so the price of the rods will be just $1 to $1.50 each. Batteries like this can be purchased in hardware stores, they are not present in the average supermarket or photography shop.

[John Cuthber]

It's probably worth adding that the carbon rods are still there in perfect working order after the battery is flat so if you know someone who uses these batteries the carbons are free.

 

BTW, my point was not that pure water is particularly useful as a conductor but that what was put forward as a "fact" simply wasn't true.

I doubt that he was using ultrapure water and ensuring that the air didn't add CO2 to it so I don't think talking about 50MV is relevant. It also fails to account for the area of the electrodes as well as their separation. Even then there would still be the fact the the insulation of the water would break down at that sort of voltage (or anything close to it).

[bob000555]

Indeed: http://www.powerlabs.org/waterarc.htm

[YT2095]

when you consider that Air is a much better conductor than pure water, I think you`ll find you`re being needlessly pedantic to the guy with his 9V battery!

 

don`t you?

 

for all intents and purposes take in the context of this thread Water doesn`t conduct at all well! and requires motile ions for his experiment to work.