On Tue, 1 Feb 2005 22:00:22 -0000, "Brian Reay"
wrote:

"Reg Edwards" wrote in message
...

It later transpired in the laboratory that when water is under relatively
high pressure, such as at the bottom of the North Sea, when in contact
with
a thick polyethylene membrane it dissasociates into hydrogen and oxygen.

The very light element diffuses through leaving heavy oxygen on the
outside.
Thus, after a few years, the air-space on the inside becomes filled with
high pressure hydrogen.

What caused this "disassociation", and where did it happen?

Water dissociates naturally to a small extent. Think of how the pH
scale is derived.

Just, I'd expect
the hydrogen to bubble off PDQ, assuming this process did occur. Also,
diffusion is the movement of something from a high to a low concentration,
assuming the mechanism is correct, I wonder how long before the
concentration would equalise (after all, the hydrogen around the cable must
have been in pretty low concentration.

It all sounds a bit like Maxwell's 'demons' but my half-educated guess
is that the polyethylene was acting as a semi-permeable membrane,
allowing only the much smaller hydrogen atoms (ions?) to pass through
under the action of the pressure differential.

"Custos Custodum" wrote in message
...
On Tue, 1 Feb 2005 22:00:22 -0000, "Brian Reay"
wrote:

"Reg Edwards" wrote in message
...

It later transpired in the laboratory that when water is under
relatively
high pressure, such as at the bottom of the North Sea, when in contact
with
a thick polyethylene membrane it dissasociates into hydrogen and
oxygen.

The very light element diffuses through leaving heavy oxygen on the
outside.
Thus, after a few years, the air-space on the inside becomes filled
with
high pressure hydrogen.

What caused this "disassociation", and where did it happen?

Water dissociates naturally to a small extent. Think of how the pH
scale is derived.

I thought the pH scale came from "per Hydronium"- H30+ ?

If the 'extra' H came from the water, then there would also be OH- to
neutralise it.


Just, I'd expect
the hydrogen to bubble off PDQ, assuming this process did occur. Also,
diffusion is the movement of something from a high to a low
concentration,
assuming the mechanism is correct, I wonder how long before the
concentration would equalise (after all, the hydrogen around the cable
must
have been in pretty low concentration.

It all sounds a bit like Maxwell's 'demons' but my half-educated guess
is that the polyethylene was acting as a semi-permeable membrane,

Semi-permeable membranes feature in osmosis, rather than diffusion (although
I have heard osmosis related to diffusion in via the concept of the solvent
diffusing ).

allowing only the much smaller hydrogen atoms (ions?) to pass through
under the action of the pressure differential.

As I recall, a hydrogen ion doesn't stay 'free' for long.

Long time since I did Chemistry, is Dr Boris not about?
--
Brian Reay
www.g8osn.org.uk
www.amateurradiotraining.org.uk
FP#898

On Wed, 2 Feb 2005 15:46:58 -0000, "Brian Reay"
wrote:

I thought the pH scale came from "per Hydronium"- H30+ ?

If the 'extra' H came from the water, then there would also be OH- to
neutralise it.

pH is defined as the negative of the logarithm of the hydrogen ion
concentration.

In pure water the product of [H+][OH-] is very close to 10exp-14,
where square brackets indicate concentrations.

Hence in pure water pH = 7 because the concetrations of the two
species are equal.

An acid solution, where [H+] is greater than that in water, has [H+]7

There is a more exact definition involving hydrogen ion activity.
--
from
Aero Spike

"Spike" wrote in message
...
On Wed, 2 Feb 2005 15:46:58 -0000, "Brian Reay"
wrote:

I thought the pH scale came from "per Hydronium"- H30+ ?

If the 'extra' H came from the water, then there would also be OH- to
neutralise it.

pH is defined as the negative of the logarithm of the hydrogen ion
concentration.

In pure water the product of [H+][OH-] is very close to 10exp-14,
where square brackets indicate concentrations.

So, if the water was being 'split', the concentrations would be the same.

Hence in pure water pH = 7 because the concetrations of the two
species are equal.

An acid solution, where [H+] is greater than that in water, has [H+]7


Ah, that sounds familar!

There is a more exact definition involving hydrogen ion activity.

That I don't recall, maybe it was beyond A level ;-)

--
Brian Reay
www.g8osn.org.uk
www.amateurradiotraining.org.uk
FP#898