What causes this color change?
gamincat
biology/environmental science teacher. I have a lab where we make ozone
detectors using potassium iodide added to a gel of corn starch and
water. When exposed to ozone, the reaction produces potassium
hydroxide, oxygen and iodine - the iodine reacts with the corn starch
to produce a blue/purple color.
I have noticed when I wash the potassium iodide gel under tap water, a
pink color often develops. Does anyone know what causes this reaction?
By the way, the directions for this ozone detector are on
www.howstuffworks.com
Thanks.
Janet Levy
SFF
Uzytkownik "gamincat" <ga...@corecomm.net> napisal w wiadomosci
news:1147797283.6...@i39g2000cwa.googlegroups.com...
>
> I have noticed when I wash the potassium iodide gel under tap water, a
> pink color often develops. Does anyone know what causes this reaction?
tap water may be ozonized or treated with gaseous chlorine
Wojtek
Salmon Egg
<any...@anycompany.com> wrote:
>> I have noticed when I wash the potassium iodide gel under tap water, a
>> pink color often develops. Does anyone know what causes this reaction?
>
> tap water may be ozonized or treated with gaseous chlorine
Then what?
Bill
-- Ferme le Bush
Madalch
the iodide, giving a small amount of iodine, which turns the starch a
pale purple, which looks pink?
Madalch
Strike that- a small amount of iodide would turn the starch blue, not
pink.
Unless it's female starch...
SFF
Uzytkownik "Madalch" <tres...@gmail.com> napisal w wiadomosci
news:1147812420....@g10g2000cwb.googlegroups.com...
> Strike that- a small amount of iodide would turn the starch blue, not
> pink.
to be exact, depends on temperature
in hot tap water there will be no blue complex formation, but free iodine
may cause purple coloration
W.
Madalch
> may cause purple coloration
But iodine is yellow in aqueous solution, either free or as triiodide
ion.
Simon Dobbs
(in article <1147797283.6...@i39g2000cwa.googlegroups.com>):
> I have noticed when I wash the potassium iodide gel under tap water, a
> pink color often develops. Does anyone know what causes this reaction?
chlorine in warm tap water displaces tiny amounts of elemental iodine which
is pink- appears black in bulk crystalline solid, but vapour shows it to be
purple.
dlzc1 D:cox T:net@nospam.com N:dlzc D:aol T:com (dlzc)
"gamincat" <ga...@corecomm.net> wrote in message
news:1147797283.6...@i39g2000cwa.googlegroups.com...
...
> I have noticed when I wash the potassium iodide gel
> under tap water, a pink color often develops. Does
> anyone know what causes this reaction?
Pink color can come from the oxidation of manganese (in whatever
state) to permangante ion. If your gel contains manganese, the
chlorine in the tap water might be doing that. Hopefully the
manganese isn't already in your water, or the pink color would be
there nevertheless. And it is wild stretch that it isn't just
the iodide being oxidized...
Try "washing the potassium iodide gel" using bottled or distilled
(or filtered through a carbon filter) water. If the pink color
goes away, it could be the chlorine in the water as the trigger.
Assuming you get no color with water without chlorine, you could
add a quarter cup of household bleach to the water (per gallon,
say), and see if you get a different color change...
David A. Smith
Farooq W
N:dlzc D:aol T:com (dlzc) wrote:
> Dear gamincat:
>
> "gamincat" <ga...@corecomm.net> wrote in message
> news:1147797283.6...@i39g2000cwa.googlegroups.com...
> ...
> > I have noticed when I wash the potassium iodide gel
> > under tap water, a pink color often develops. Does
> > anyone know what causes this reaction?
>
> Pink color can come from the oxidation of manganese (in whatever
> state) to permangante ion. If your gel contains manganese, the
> chlorine in the tap water might be doing that. Hopefully the
> manganese isn't already in your water, or the pink color would be
> there nevertheless.
I think this is not true. Chlorine concentration in water is too small
to oxidize manganese to permanganate. Secondly permanganate is a much
stronger oxidizing agent than chlorine It is the other way round, MnO4
(-) can oxidize chloride ion to chlorine.
I think that iodine has a sufficient vapor pressure. If the OP oxidizes
KI to iodine with ozone, the iodine may exist as a triiodie ion, some
of which is bound to starch. When he dilutes the solution in the sink,
triiodide ion converts back to free iodine and iodide ion. Iodine
having purple/pink vapor makes the water look pinkish.
A friend recently emailed Humphry Davy's article (1814) when he was
experimenting iodine The title was interesting "Some experiments on
subject and observations on a substance which becomes violet colored
gas by heat" ..."A new and a very curious substance that has recently
occupied the attention of chemists in Paris".
Most likely this mystery pink is iodine vapor. Otherwise the OP might
be discovering a new reaction in sink, recall an important discovery in
a laboratory sink was the concept of EDTA titration indicators!
> Assuming you get no color with water without chlorine, you could
> add a quarter cup of household bleach to the water (per gallon,
> say), and see if you get a different color change...
Yes hypochlorite could oxidize Mn species to MnO4(-) under severe
conditions (boiling).
M. Farooq
dlzc1 D:cox T:net@nospam.com N:dlzc D:aol T:com (dlzc)
"Farooq W" <faro...@gmail.com> wrote in message
news:1147834384.0...@38g2000cwa.googlegroups.com...
>
> N:dlzc D:aol T:com (dlzc) wrote:
>> Dear gamincat:
>>
>> "gamincat" <ga...@corecomm.net> wrote in message
>> news:1147797283.6...@i39g2000cwa.googlegroups.com...
>> ...
>> > I have noticed when I wash the potassium iodide gel
>> > under tap water, a pink color often develops. Does
>> > anyone know what causes this reaction?
>>
>> Pink color can come from the oxidation of manganese
>> (in whatever state) to permangante ion. If your gel
>> contains manganese, the chlorine in the tap water might
>> be doing that. Hopefully the manganese isn't already in
>> your water, or the pink color would be there nevertheless.
>
> I think this is not true.
With free chlorine (which is what I was thinking too) you are
correct. Where does the oxygen come from?
> Chlorine concentration in water is too small to oxidize
> manganese to permanganate. Secondly permanganate is
> a much stronger oxidizing agent than chlorine It is the
> other way round, MnO4 (-) can oxidize chloride ion to
> chlorine.
Some municipalities use chlorine dioxide as a primary
disinfectant. Chlorine dioxide can form permanganate. And is
really a side issue, since we don't know if his "gel" contains
manganese.
> I think that iodine has a sufficient vapor pressure. If
> the OP oxidizes KI to iodine with ozone, the iodine
> may exist as a triiodie ion, some of which is bound to
> starch. When he dilutes the solution in the sink,
> triiodide ion converts back to free iodine and iodide
> ion. Iodine having purple/pink vapor makes the water
> look pinkish.
Sounds reasonable. Also, if his gel spends a variable amount of
time being exposed to air (and its variable ozone load), he would
potentially get the "once in a while" pink coloration.
> A friend recently emailed Humphry Davy's article
> (1814) when he was experimenting iodine The title
> was interesting "Some experiments on subject and
> observations on a substance which becomes violet
> colored gas by heat" ..."A new and a very curious
> substance that has recently occupied the attention
> of chemists in Paris".
>
> Most likely this mystery pink is iodine vapor.
> Otherwise the OP might be discovering a new
> reaction in sink, recall an important discovery in
> a laboratory sink was the concept of EDTA titration
> indicators!
>
>
>> Assuming you get no color with water without
>> chlorine, you could add a quarter cup of household
>> bleach to the water (per gallon, say), and see if
>> you get a different color change...
>
> Yes hypochlorite could oxidize Mn species to
> MnO4(-) under severe conditions (boiling).
The hypochlorite wouldn't last too long...
Thanks for catching my glaring errors!
David A. Smith
dlzc1 D:cox T:net@nospam.com N:dlzc D:aol T:com (dlzc)
"Farooq W" <faro...@gmail.com> wrote in message
news:1147834384.0...@38g2000cwa.googlegroups.com...
I find reference to a "pink" result on page 3 of this pdf, bullet
point #4, as the "non-desired" result...
http://www.pubmedcentral.gov/picrender.fcgi?artid=1259473&blobtype=pdf
... and here, second paragraph
http://www.novozymes.com/library/Publications/Biotimes_Sprog/Biotimes_2005/3-05/GB_colour.pdf
Quite a few more using Google with all the words:
iodine starch color pink
David A. Smith