Question:
I'm sorry for posting this to two groups but I was not sure
which area this falls better into. 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?
Answer:
Okay, I'm getting the concept of the reaction of e- plus H2O with NaCl.
To make sure, what you're saying is that the H2O + e- produces H2 and
also OH-. Cl- is attracted from the NaCl leaving some Na+ floating
around which binds (not sure that's the correct chemistry term) with
OH- forming NaOH in the solution, Cl- at the (presumably) positive
electrode, and H2 at the (presumably) negative terminal?
This leaves me with a couple of questions. 1) I thought the purpose of
electrolysis of water was to generate O2 and H2, but my experiment (if
you can call something so simple as what I did an "experiment") shows
me that it's actually, with NaCl as the electrolyte, producing Cl- and
H2, not what I wanted or expected. When I studied this stuff in high
school it was preached to produce H2 and O2, under what circumstances
can that happen? It seems that the electrolyte is playing a part in
the chemical changes and is contributing some parts to it (hence the
Cl- gas), so it would seem that even using baking soda would still
produce something other than H2 and O2, as you suggest ("not sure if it
produces O2..."). 2) if I can't get O2 from the sodium chloride
electrolyte solution (which isn't a big deal since I can get it from
the atmosphere), what can I do with a bunch of NaOH water? What is
sodium hydroxide and what good is it? More importantly, is it harmful?
If I'm splitting out a bunch of salt water to H2 and Cl- gasses and
I'm left with gallons of NaOH water, what can I do with it? Is there a
process that I could use to reapply the Cl- to the water and re-join
the Cl- to the Na of the NaOH and get NaCl again?
