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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Electrolysis of water as a science fair project
Q. I am working on a water electrolysis project, and I need some information. How much hydrogen and oxygen are in a cubic meter of water. How many watts are required to convert this much water. After the hydrogen and oxygen are re-combusted how much water is there? how many btu's in this much hydrogen and oxygen.
John R [last name deleted for privacy by Editor]- Sudbury, Ontario, Canada
2002
A. John, the readers are more than willing to help students with their science projects, but we try to balance this with the constant pleas from teachers who ask us to please just tell the students to do their own homework.
So ... all of the calculations will be worked from the weight (or mass) of the water. So, first, what is the mass of that volume of water? What is the molecular formula for water? What are the atomic masses of hydrogen, oxygen, and water? Got the answer for your first question now?
Your second question is the hard one. If you were provided with the factors you needed, how would you begin to approach it? I'd start with Faraday's Law.
If you don't know the answer to your third question, you've never heard of the law of conservation of mass -- return to general science :-)
The fourth question is simply a matter of applying a conversion factor, right, because Watt-hours and BTU's are a measure of the same thing. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002
Q. I am trying to do a school science fair project proving that water is indeed 2 parts hydrogen to 1 part oxygen. I am using two 6V batteries, a large glass beaker [beakers on eBay or Amazon [affil links] , insulated copper wires, two glass test tubes, two graphite pencils, distilled water, and baking soda [in bulk on eBay or Amazon [affil links] . I have gotten my electrolyte solution correct so that my ratio is the 2:1 that it should be so I have shown what I set out to do. My problem is that one of the rules of my Science Fair is I must have variables listed in my project. What would they be, if any? I can't think of what they would be.
Torger T. [last name deleted for privacy by Editor]Student - Tennessee, USA
2006
A. I enjoyed your question, Torger; it is quite thought provoking. And I'm glad to see that you had the insight to appreciate your quandary. Here's the problem:
The structure of your project and hypothesis allows no variables. It's a yes/no, go/no-go thing. Is water comprised of two parts hydrogen and one part oxygen? Yes. Done. You demonstrated ('proved' might be too strong a word) that water is two parts hydrogen, not one or three no matter what you vary.
You could change your experiment, altering either the voltage or the baking soda concentration to make it into a "rate" experiment. Or, better, you could find a voltage below which no electrolysis occurs, then the variable would be voltage. But frankly, the 'rules' are the problem, not your excellent experiment.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I am actually performing electrolysis on salt water for my science fair demonstration. I have removed graphite rods from a battery, secured them to a lantern battery and then inserted them into saltwater covered with test tubes filled with water. I get hydrogen, no problem, but oxygen is proving tough.
The first time I had real erosion problems and the water turned blue. So, I removed the copper wiring attaching the graphite rod to the positive batter cable and changed to a "silver" wire. Now, I am getting a white, milky substance instead of oxygen. What am I doing wrong?
Jr. High Student - Sparta, New Jersey
2007
Q. While performing electrolysis of water by adding sulfuric acid in it and using graphite electrodes it was seen that at anode black powder sort of material was precipitated and at cathode maroonish coloured layer formed on graphite rod!
what is the black substance? is it carbon? can I titrate the solution?
and what is the maroon layer and by what mechanism it is formed?
hobbyist - Indore, MP, India
June 15, 2009
How can science teacher make the electrolysis of water go faster?
My name is Josephine Demerre. I'm a science teacher at PSJA High School in Hidalgo County, Texas. I'm trying to design an electrolysis of water experiment for my students. I tried to combine and modify several procedures that I have come across. I ended up using stainless steel fishing lines as electrodes which I covered with insulators that contract when heated. I mixed NaOH solution to the water and used 9 V battery. The result is not as fast as I want it to be. I also noticed a lot of froth forming. Can you suggest how to improve the setup?
Josephine Demerreteacher - Pharr, Texas, USA
May 12, 2010
A. Good Moooooorninggg Miss Demerre (sorry I had a flashback there).
Try putting two batteries in parallel (same 9 volts, twice as much available current). Faraday's Law of Electrolysis applies here, and the amount of water hydrolized is directly proportional to the current. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 12, 2010
A. More current is going to depend on the spacing of the anode to the cathode, the size of each, the conductivity of the water and the voltage applied.
I would personally use a very dilute solution of sulfuric acid as it is completely ionized and has nothing that would induce frothing.
Table salt is cheaper and safer, but you will get chlorine evolving off of the anode as soon as you exceed the minimum voltage for the chlorine to come off.
One problem is that your anode and cathode are too small to generate a reasonable amount of gas. I would run insulated copper wire to alligator clips and then clip it to the blade portion of stainless steel knives that I get at the dollar store.
James Watts
- Navarre, Florida
May 13, 2010
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