semi off-topic: how to clean ferrichloride stains

[JosephKK]

PH per se is a separate issue from redox.

It is, but they are all equilibria. ;-)

Since we're going to invoke chemistry, I'm just going to go overboard and
rattle off some stuff here: ;-)

Hydroxy:
Fe(OH)3 <--> Fe(3+) + 3 OH- pKs = 38.8
Fe(3+) + H2O <--> FeOH(2+) + H+ pKa = 2.19
Fe(OH)(2+) + H2O <--> Fe(OH)2(+) + H+ pKa = 2.41
Fe(OH)2(+) + H2O <--> Fe(OH)3(aq) + H+ pKa = 7.97
(Note this doesn't include the solubility of the Fe(OH)3 species.)
Chelates:
Fe(3+) + EDTA(4-) <--> [FeEDTA]- pKf = -25.1
Chlorides:
Fe(3+) + Cl- <--> FeCl(2+) pKf1 = -1.48
FeCl(2+) + Cl- <--> FeCl2(+) pKf2 = -0.65
FeCl2(+) + Cl- <--> FeCl3(aq) pKf3 = 1.00
Oxalates:
Fe(3+) + C2O4(2-) <--> [FeC2O4]+ pKf1 = -7.54
[FeC2O4]+ + C2O4(2-) <--> [Fe(C2O4)2)]- pKf2 = -7.05
[Fe(C2O4)2]- + C2O4(2-) <--> [Fe(C2O4)3)](3-) pKf3 = -5.41
(So total pKf = 20.00.)
Citrate:
Fe(3+) + Cit(3-) <--> [FeCit](aq) pKf = -11.8
Redox:
Fe(3+) + e- <--> Fe(2+) Eo = 0.771 V
SO4(2-) + H2O + 2e- <--> SO3(2-) + 2OH- Eo = -0.936 V
(Hmm, that's in alkali.)

So: Fe(OH)3 is damned insoluble; Fe(3+) is pretty acidic (as aqueous ions
go); FeCl3 is somewhat more soluble, but it still takes a lot of chloride
and acid to overcome the insolubility of Fe(OH)3; chelates like EDTA, et
al., oxalate, citrate, etc. grab on real tight, solvating iron well; and a
variety of reducing agents will suffice, but only if you get the iron into
solution to react with it.

Tim

I don't suppose that you would consider trying to analyze the impact
of sodium bismuthate and sodium bisulfite on the ferrous chloride /
ferric chloride / cuprous chloride / cupric chloride / ferric
hydroxide solutions.

Yes there is usually all those species and more when ferric chloride
is used as a copper echant.

 

[The Phantom]

PH per se is a separate issue from redox.

It is, but they are all equilibria. ;-)

Since we're going to invoke chemistry, I'm just going to go overboard and
rattle off some stuff here: ;-)

Hydroxy:
Fe(OH)3 <--> Fe(3+) + 3 OH- pKs = 38.8
Fe(3+) + H2O <--> FeOH(2+) + H+ pKa = 2.19
Fe(OH)(2+) + H2O <--> Fe(OH)2(+) + H+ pKa = 2.41
Fe(OH)2(+) + H2O <--> Fe(OH)3(aq) + H+ pKa = 7.97
(Note this doesn't include the solubility of the Fe(OH)3 species.)
Chelates:
Fe(3+) + EDTA(4-) <--> [FeEDTA]- pKf = -25.1
Chlorides:
Fe(3+) + Cl- <--> FeCl(2+) pKf1 = -1.48
FeCl(2+) + Cl- <--> FeCl2(+) pKf2 = -0.65
FeCl2(+) + Cl- <--> FeCl3(aq) pKf3 = 1.00
Oxalates:
Fe(3+) + C2O4(2-) <--> [FeC2O4]+ pKf1 = -7.54
[FeC2O4]+ + C2O4(2-) <--> [Fe(C2O4)2)]- pKf2 = -7.05
[Fe(C2O4)2]- + C2O4(2-) <--> [Fe(C2O4)3)](3-) pKf3 = -5.41
(So total pKf = 20.00.)
Citrate:
Fe(3+) + Cit(3-) <--> [FeCit](aq) pKf = -11.8
Redox:
Fe(3+) + e- <--> Fe(2+) Eo = 0.771 V
SO4(2-) + H2O + 2e- <--> SO3(2-) + 2OH- Eo = -0.936 V
(Hmm, that's in alkali.)

So: Fe(OH)3 is damned insoluble; Fe(3+) is pretty acidic (as aqueous ions
go); FeCl3 is somewhat more soluble, but it still takes a lot of chloride
and acid to overcome the insolubility of Fe(OH)3; chelates like EDTA, et
al., oxalate, citrate, etc. grab on real tight, solvating iron well; and a
variety of reducing agents will suffice, but only if you get the iron into
solution to react with it.

Tim

I don't suppose that you would consider trying to analyze the impact
of sodium bismuthate and sodium bisulfite on the ferrous chloride /
ferric chloride / cuprous chloride / cupric chloride / ferric

You must mean something else other than sodium bismuthate for a reducing
agent. It's a very strong oxidizing agent. See:
http://www.newi.ac.uk/buckleyc/titrat.htm

Maybe you're thinking of something like sodium dithionite.

 

[The Phantom]

Well how about that. I misremember ed after 30 or 40 years.

You have that problem too?

I thought I remembered right, but I looked it up in my old Semimicro
Quantitative Analysis book to be sure!

Turns out sodium bismuthate is the reagent used to detect manganese. It
can oxidize maganese to permanganate ion, which is the detected by its
purple color. One normally thinks of (potassium) permanganate as a
powerful oxidizer, but bismuthate can oxidize manganese in a low oxidation
state all the way to permanganate.

 

[Tim Williams]

Turns out sodium bismuthate is the reagent used to detect manganese. It
can oxidize maganese to permanganate ion, which is the detected by its
purple color. One normally thinks of (potassium) permanganate as a
powerful oxidizer, but bismuthate can oxidize manganese in a low oxidation
state all the way to permanganate.

Bleach (hypochlorite) too. In fact, bleach is a suprisingly strong
oxidizer, not something you'd expect for off-the-shelf products!

Tim

 

[The Phantom]

Bleach (hypochlorite) too. In fact, bleach is a suprisingly strong
oxidizer, not something you'd expect for off-the-shelf products!

Are you saying that hypochlorite can oxidize manganous to permanganate?

I gave it a try, and under both alkaline and acidic conditions I didn't see
any purple color (using Clorox for the hypochlorite). But I did get a
definite purple with bismuthate. Is some special condition needed?

By the way, have you noticed that Clorox currently on the store shelves is
6.00%, but I'm sure it used to be 5.25%? Is this a comment on the state of
our culture? Things are dirtier now, and need a more powerful bleach?

And, speaking of products available off-the-shelf--hydrogen peroxide in the
35% food grade concentration. That stuff is dangerous.

Furthermore, I noticed that Home Depot is selling gallon jugs of
concentrated sulfuric acid as a drain opener!

 

[Jim Thompson]

Are you saying that hypochlorite can oxidize manganous to permanganate?

I gave it a try, and under both alkaline and acidic conditions I didn't see
any purple color (using Clorox for the hypochlorite). But I did get a
definite purple with bismuthate. Is some special condition needed?

By the way, have you noticed that Clorox currently on the store shelves is
6.00%, but I'm sure it used to be 5.25%? Is this a comment on the state of
our culture? Things are dirtier now, and need a more powerful bleach?

And, speaking of products available off-the-shelf--hydrogen peroxide in the
35% food grade concentration. That stuff is dangerous.

Furthermore, I noticed that Home Depot is selling gallon jugs of
concentrated sulfuric acid as a drain opener!

Ha! Just look at Ace Hardware for all the interesting things you can
buy by the gallon ;-)

...Jim Thompson

 

[Tim Williams]

Are you saying that hypochlorite can oxidize manganous to permanganate?

I gave it a try, and under both alkaline and acidic conditions I didn't see
any purple color (using Clorox for the hypochlorite). But I did get a
definite purple with bismuthate. Is some special condition needed?

Alkaline should do it; manganate (rather than permanganate) may be
necessary (i.e. hell ass damn alkaline). Yields suck nard, but it can turn
color.

By the way, have you noticed that Clorox currently on the store shelves is
6.00%, but I'm sure it used to be 5.25%? Is this a comment on the state of
our culture? Things are dirtier now, and need a more powerful bleach?

Heh...who knows.

And, speaking of products available off-the-shelf--hydrogen peroxide in the
35% food grade concentration. That stuff is dangerous.

I haven't seen it around, just at random anyway. Another excellent
oxidizer for sure, and good for some coordination chemistry (blue
peroxychromate, red peroxytitanate, etc.).

Furthermore, I noticed that Home Depot is selling gallon jugs of
concentrated sulfuric acid as a drain opener!

I get the red bottle stuff, Liquid Fire, from Ace Hardware. I think they
recently reformulated; the stuff I bought last month came sealed in a
plastic bag (heh, I wonder if they were having too many accidents..) and is
darker in color. I don't have large enough Pyrex glassware (..or balls..)
to boil it out, so I use it as-is. Still works fine.

Tim

 

[JosephKK]

You have that problem too?

I have started noticing recently.

I thought I remembered right, but I looked it up in my old Semimicro
Quantitative Analysis book to be sure!

Turns out sodium bismuthate is the reagent used to detect manganese. It
can oxidize maganese to permanganate ion, which is the detected by its
purple color. One normally thinks of (potassium) permanganate as a
powerful oxidizer, but bismuthate can oxidize manganese in a low oxidation
state all the way to permanganate.

Oh, Yeah. That is one powerful oxidizer. In pure form it is a bit
yellowish as well.