| Author |
Message |
Mike Monett
Guest
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 Posted:
Wed Jul 13, 2005 12:35 am Post subject:
Re: OH- spread more than H+ ions? |
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Aubrey McIntosh, Ph.D. wrote:
[...]
| Quote: | Not all antifreeze use this same dye, but in principle, yes. As an
aside, when ethylene glycol (of antifreeze) oxidizes it can make oxalic
acid. Oxalic acid and iron can proceed to make "greensalt" which is
almost the same color as antifreeze with the disodium fluorescein.
Most pH indictors are discussed in the context of either H+ or Na+ (OH-
in water, with Na+ as a spectator ion) If metals that are not in the
first two columns are used, you results have a lot more nuance than the
standard language provides. For example, when I cook cabbage in an
aluminum container, the color is off, and the container shows signs that
some aluminum oxide is removed. I assume that the Al+3 is being
complexed by the dye in the cabbage, but this is anecdotal -- I haven't
collected data.
One easy dye to obtain is the broth from cooking red cabbage. It is red
when acidic, blue when basic, and lavender in betwixt.
Bromthymol blue is another easy to obtain pH indicator. It is sold in
aquarium shops as a treatment for "ick."
Litmus paper itself uses the juice from lichens. It sticks in my mind
that the Scientific American "Connections" column attributes Litmus
paper to a McIntosh in Scotland.
Beet juice is mentioned at http://www.purchon.com/chemistry/ph.htm but I
have not tried it. I do know that when beets are cut into 1/4" cubes
and cooked while protected from air in a pressure cooker, the juice is a
dayglow red. I speculate that this is pH sensitive, I just haven't had
the desire to add lye or battery acid to my beets.
Other foods: cranberry, elderberry, tumeric, grape, and blueberry are
mentioned at http://www.vanderbilt.edu/vsvs/
lesson_plans/NaturalIndicators.doc
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Thanks for the good info. Incidentally, red cabbage turns very deep
purple when exposed to OH(-) ions, and very faint white with AG(+) ions.
Mike Monett
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John Beardmore
Guest
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| Posted:
Wed Jul 13, 2005 12:35 am Post subject:
Re: OH- spread more than H+ ions? |
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In message <1121012726.743338.221040@g47g2000cwa.googlegroups.com>,
WAYNEL <mail@wlawson.com> writes
| Quote: | I've conducted a simple experiment on a glass sample that has two clean
copper electrodes biased with 20v DC. Between the two electrodes I
have placed a drop of de-ionised water with Universal Indicator added.
Over a period of time the electrodes changes colour, as expected, with
the cathode going purple (OH-) and the anode going red (H+).
After a longer period of time the colours start to spread out toward
the opposing electrodes, pH gradient. However, the amount the purple
(OH-)spreads is apx three times greater that that of the red (H+).
I have repeated this 10 times in random positions and I get the same
results.
I would have thought that the H+ ions would have more mobility than the
OH- ions and thus I would have expected the opposite to happen.
Can anyone help and through some light on this phenomena, or have I
missed something?
|
What is the effect of the charge gradient on the constituents of the
indicator itself ?
Cheers, J/.
--
John Beardmore |
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Rich Grise
Guest
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| Posted:
Wed Jul 13, 2005 10:20 pm Post subject:
Re: OH- spread more than H+ ions? |
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On Sun, 10 Jul 2005 09:25:26 -0700, WAYNEL wrote:
| Quote: | I've conducted a simple experiment on a glass sample that has two clean
copper electrodes biased with 20v DC. Between the two electrodes I
have placed a drop of de-ionised water with Universal Indicator added.
Over a period of time the electrodes changes colour, as expected, with
the cathode going purple (OH-) and the anode going red (H+).
After a longer period of time the colours start to spread out toward
the opposing electrodes, pH gradient. However, the amount the purple
(OH-)spreads is apx three times greater that that of the red (H+).
I have repeated this 10 times in random positions and I get the same
results.
I would have thought that the H+ ions would have more mobility than the
OH- ions and thus I would have expected the opposite to happen.
Can anyone help and through some light on this phenomena, or have I
missed something?
|
I suspect you've got some dissolved copper in there, in some
form. What happens if you use gold-plated electrodes, like wire-wrap
pins?
Thanks,
Rich
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Marvin
Guest
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| Posted:
Wed Jul 13, 2005 10:33 pm Post subject:
Re: OH- spread more than H+ ions? |
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John Beardmore wrote:
| Quote: | In message <1121012726.743338.221040@g47g2000cwa.googlegroups.com>,
WAYNEL <mail@wlawson.com> writes
I've conducted a simple experiment on a glass sample that has two clean
copper electrodes biased with 20v DC. Between the two electrodes I
have placed a drop of de-ionised water with Universal Indicator added.
Over a period of time the electrodes changes colour, as expected, with
the cathode going purple (OH-) and the anode going red (H+).
After a longer period of time the colours start to spread out toward
the opposing electrodes, pH gradient. However, the amount the purple
(OH-)spreads is apx three times greater that that of the red (H+).
I have repeated this 10 times in random positions and I get the same
results.
I would have thought that the H+ ions would have more mobility than the
OH- ions and thus I would have expected the opposite to happen.
Can anyone help and through some light on this phenomena, or have I
missed something?
What is the effect of the charge gradient on the constituents of the
indicator itself ?
|
If they are charged, they will migrate in a direction and at a rate depending on the gradient.
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Rich Grise
Guest
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| Posted:
Wed Jul 13, 2005 10:48 pm Post subject:
Re: OH- spread more than H+ ions? |
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On Tue, 12 Jul 2005 10:58:31 -0400, Mike Monett wrote:
| Quote: | Aubrey McIntosh, Ph.D. wrote:
[...]
Another indicator that might be interesting is disodium fluorescein.
This is the stuff that makes antifreeze the dayglow green color. It is
safe enough to inject into blood or pour into rivers for tracing.
It changes from an extreemly efficient fluorescent dye to colorless and
non-fluorescent when it gets protonated.
Interesting. You mean I can go out to my car, drain some antifreeze, and
get a ph indicator? That would be nice.
I'm not sure what you mean by the word protenate in this context. Does it
mean the indicator responds only to hydronium ions, or would any
postive ion such as metal work?
Any other suggestions for cheap sensitive indicators, preferably ones you
can find in a grocery store or pharmacy on a weekend?
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Do you mean besides red cabbage juice? That's almost free, and I saw a
demo on some TV show - either the science segment of some variety show,
or something like that Newton's Apple. Anyway, they juiced a cabbage,
and had about seven containers, where they put stuff like vinegar, and
drain cleaner, and ammonia, and various things, with different pH, and
that cabbage juice turned about seven different colors!
But then you have the same problem with all kinds of chemical compounds -
I think the indicator is called a "confounder".
Is there any such thing as a noninvasive pH meter?
Thanks,
Rich |
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Rich Grise, but drunk
Guest
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| Posted:
Thu Jul 14, 2005 12:35 am Post subject:
Re: OH- spread more than H+ ions? |
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On Wed, 13 Jul 2005 13:33:22 -0400, Marvin wrote:
| Quote: | John Beardmore wrote:
In message <1121012726.743338.221040@g47g2000cwa.googlegroups.com>,
WAYNEL <mail@wlawson.com> writes
I've conducted a simple experiment on a glass sample that has two clean
copper electrodes biased with 20v DC. Between the two electrodes I
have placed a drop of de-ionised water with Universal Indicator added.
Over a period of time the electrodes changes colour, as expected, with
the cathode going purple (OH-) and the anode going red (H+).
After a longer period of time the colours start to spread out toward
the opposing electrodes, pH gradient. However, the amount the purple
(OH-)spreads is apx three times greater that that of the red (H+).
I have repeated this 10 times in random positions and I get the same
results.
I would have thought that the H+ ions would have more mobility than the
OH- ions and thus I would have expected the opposite to happen.
Can anyone help and through some light on this phenomena, or have I
missed something?
What is the effect of the charge gradient on the constituents of the
indicator itself ?
If they are charged, they will migrate in a direction and at a rate depending on the gradient.
|
Would viscosity have anything to do in this equation?
Thanks,
Rich |
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Roger Johansson
Guest
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| Posted:
Thu Jul 14, 2005 6:12 am Post subject:
Re: OH- spread more than H+ ions? |
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Rich Grise, but drunk wrote:
| Quote: | What is the effect of the charge gradient on the constituents of
the >> indicator itself ?
If they are charged, they will migrate in a direction and at a rate
depending on the gradient.
Would viscosity have anything to do in this equation?
|
Just an idea about indicator in the liquid.
It is possible to remove small samples of the liquid to test it, so
the indicator does not compromise the experiment.
One way of doing it is to put the liquid in long tubes or ditches, so
any change has to move along a certain path.
Then we can take up a few milli-liters at certain locations at certain
points in time and add a pH indicator to each test sample.
--
Roger J. |
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Herman Family
Guest
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| Posted:
Thu Jul 14, 2005 6:58 am Post subject:
Re: OH- spread more than H+ ions? |
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"Roger Johansson" <no-email@no.invalid> wrote in message
news:xn0e4q4jwh2c8lu000@news.sunsite.dk...
| Quote: | Rich Grise, but drunk wrote:
What is the effect of the charge gradient on the constituents of
the >> indicator itself ?
If they are charged, they will migrate in a direction and at a rate
depending on the gradient.
Would viscosity have anything to do in this equation?
Just an idea about indicator in the liquid.
It is possible to remove small samples of the liquid to test it, so
the indicator does not compromise the experiment.
One way of doing it is to put the liquid in long tubes or ditches, so
any change has to move along a certain path.
Then we can take up a few milli-liters at certain locations at certain
points in time and add a pH indicator to each test sample.
--
Roger J.
|
You might see some sort of an effect due to the seventeen fold difference in
mass of the two ions.
Michael |
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John Savage
Guest
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| Posted:
Fri Jul 15, 2005 12:35 am Post subject:
Re: OH- spread more than H+ ions? |
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Mike Monett <no@spam.today> writes:
| Quote: | Any other suggestions for cheap sensitive indicators, preferably ones you
can find in a grocery store or pharmacy on a weekend?
|
When I was a high school student I discovered I could make a pH indicator
from the juice of inkweed berries. It remained purple at one end of the
scale and changed to green at the other. Inkweed is found growing in rocky
waste ground such as around a heap of illegally dumped builder's brick
rubble. :-)
I presume that inkweed is a European weed introduced here (Australia),
but to describe it just picture a small dock plant with glossy fruit that
looks like a mulberry and undergoes the same red-->black colour transition
as it matures but instead of being spherical the fruit is cylindrical
about 5 cm in length.
ObElectronics: I have previously posted on my experiments with the
fascinating electrolytic rectifer: a beaker of sodium bicarbonate solution
and two metal electrodes--this might interest experimenters.
--
John Savage (my news address is not valid for email) |
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WAYNEL
Guest
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| Posted:
Fri Jul 15, 2005 3:33 pm Post subject:
Re: OH- spread more than H+ ions? |
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I thought that cation have grater mobility than anions?
WayneL |
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