First, the semantic question: electrons are called negative, so a positive ion is missing one or more electrons.
Second, the hydrolysis question. Whatever gas forms will consist of
neutral molecules. I'm no sure what you mean by 'hydroxide' gas. I
suppose there could be a tiny amount of hydrogen peroxide, H2O2, but
it's less stable than a water- O2 combination, so you shouldn't get
much. You'd have to look up some redox potentials or ask somebody more
competent whether in the presence of high Cl- concentrations (e.g. from
NaCl) you might get Cl2 rather than O2. If you use a basic solution,
with the main negative ion being OH-, that won't be a problem. At the
other electrode, you should only get H2 gas, because most of the
typical positive ions that might be around (Na+, etc ) would plate out
as solids, not gases. At any rate, the common experience with
reasonably pure water is that you get H2 at one electrode and O2 at the
other.
Mike W.
Sodium plating on an electrode immersed in water won't happen
because metallic sodium reacts instantly with the water to form sodium
ions, hydroxide ions (which stay in solution), and hydrogen gas, which
may bubble off (it's the same electrode the hydrogen bubbles off of
anyway so you wouldn't notice a difference with the salt present on
that side. I can't say much about the chlorine -- it might dissolve in
the water). Hydrogen peroxide also is fairly soluble in water, so I
wouldn't imagine much of that would come off as a gas.
Tom
(published on 10/22/2007)
