Question:
I'm just a layman and I'm trying to
do some very simple (I think it is/should be) chemistry/physics of
creating H2 and O2 from water with an electric current (electrolysis)
and I'm having some problems.
First and foremost is that I am only lightly versed in chemistry and
physics so I'm just playing with someone else's toys here; I don't
understand all the stuff that makes this happen which means I'm pretty
much in the dark about a bunch of things about electrolysis of water,
so I'm sorry for the base need of information and, in advance, my poor
initial understanding of any high-level explanations.
The Problem: I took some warm tapwater (which has some salt (sodium
chloride, but I'll use "salt" from here on) in it already due to water
"softening" by replacing unwanted minerals from "hard" water with salt
ions) and added a splash of salt (out of a cylindrical, pour-spout
container; maybe 1 tablespoon of salt (not iodized) in about 12 oz of
water) and stirred it in. Then I took two pieces of graphite
(presumably graphite, they were the "lead" from a couple of Home Depot
carpenters' pencils (the wide, flat kind)) and made electrical
connection to them via a pair of alligator test leads. I then applied
approximately 5 volts DC from a variable power supply and notice
bubbles at both electrodes.
That is what I expected, here are the major problems I have:
First, the bubbles from neither lead produced flame when a flame was
applied to the surface area of the water in the vicinity of the
bubbles. Perhaps my amounts of H2 (I tested both leads in case I was
wrong about which lead was producing H2 and which was producing O2)
were too small to burn or burn consistently, however, I seem to
remember from 15 or so years ago from high school, that it would flame.
Second, the water started turning lightly brown, but this may have been
due to the fact that one of my alligator lead clips was in contact with
the water and, subsequently, turned brown as if (and I think it did) it
rusted.
Finally, and this really is driving me nuts, I noticed a distinct smell
of chlorine from the glass of water. It was so strong, in fact, that
after only a few minutes of running my experiment (maybe 5 minutes) my
girlfriend in the other room (20 or so feet away) commented on the
odor.
In summation, what I seem to have is A) the ability to pass electric
current through a salt-water and no produce hydrogen, B) the ability to
taint the water and cause it to turn brown (perhaps the rusting of the
alligator clip), and C) the ability to produced chlorine gas (or
similar-smelling gas) from salt water when subjected to electrolysis.
All I wanted was some O2 and some H2. I thought this was some really
basic chemistry/physics stuff. I did this stuff when I was much
younger (maybe 15 or 20 years ago) and made little flames out of the
gases produced. Any clues what I'm doing wrong from my description?
Am I just misunderstanding my results or am I doing something wrong
from the get-go?
Thank you for your time, knowledge, help, and mostly for tolerating
someone who's way out of his depth but wants to learn.
Answer:
Question: however, I seem to
remember from 15 or so years ago from high school, that it would flame. Answer: Maybe you were producing hydrogen more quickly then.
Question: Second, the water started turning lightly brown, but this may have been
due to the fact that one of my alligator lead clips was in contact with
the water and, subsequently, turned brown as if (and I think it did) it
rusted. Answer: If you have metal (represented below by M) at the positive electrode
exposed to the solution, you'll get a reaction like:
M -> M++ + 2 e-
2 H20 + 2 e- -> 2 OH- + H2
Or something similar, depending on the valence of the metal. For a lot
of metals, the resulting metal ions will precipitate out of solution in
the form of insoluble metal oxides, which will discolor the water.
Question: Finally, and this really is driving me nuts, I noticed a distinct smell
of chlorine from the glass of water. It was so strong, in fact, that
after only a few minutes of running my experiment (maybe 5 minutes) my
girlfriend in the other room (20 or so feet away) commented on the
odor.
In summation, what I seem to have is A) the ability to pass electric
current through a salt-water and no produce hydrogen, B) the ability to
taint the water and cause it to turn brown (perhaps the rusting of the
alligator clip), and C) the ability to produced chlorine gas (or
similar-smelling gas) from salt water when subjected to electrolysis. Answer: It's chlorine. It comes from the salt (sodium chloride). The reaction
goes like:
2 H20 + 2 e- -> 2 OH- + H2
2 Cl- -> 2 e- + Cl2
And leaves sodium hydroxide (NaOH) in the solution.
When I was doing this sort of stuff at home while I was in high school,
I used baking soda (sodium bicarbonate, NaHCO3) instead of salt as the
electrolyte whenever I was doing stuff inside. I'm not sure whether it
produces oxygen at the positive terminal, but at least it didn't
produce chlorine. It was slower than the salt, though.
