# Modern Rodinal Substitutes

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• 08-29-2009, 09:30 AM
Kirk Keyes
Quote:

Originally Posted by gainer
A pinch? I thought that was against your religion. How many milligrams in a pinch?:p

I take the pinch out of the rest of the sulfite that I measured with my precise balance. ;^)
• 08-29-2009, 09:32 AM
Kirk Keyes
Quote:

Originally Posted by gainer
If I add anything before the metol, it will be a little ascorbic acid. That is to assure that any oxidized Metol that might be in my supply will be regenerated before I add the sulfite.

I suspect that you can add ascorbate to water to remove dissolved oxygen just like you can sulfite. Ascorbate is often used in the lab setting to remove other stronger oxidizers like chlorine.
• 08-29-2009, 09:44 AM
Kirk Keyes
Quote:

Originally Posted by Sean
fyi- I've had to edit some bickering out of this thread and get it back on topic.

Sean

WOW - I made it without any deletions this time!
• 08-29-2009, 09:47 AM
gainer
Quote:

Originally Posted by Kirk Keyes
Bill - are you saying you are suprised that a 3% solution of potassium hydroxide has a pH of 14? If so, here's the way to calculate it.

A 3% solution is about 0.53M KOH.
Calculate pOH first:
pOH = -log10[OH-]
pOH = -log10[0.53M]
pOH = 0.276
Then calculate pH:
pH = 14 - pOH
pH = 14 - 0.276
pH = 13.72

A 0.53M KOH solution should have a pH of about 13.7. That's close enough to pH 14 for my book.

If that's not what you are saying, then don't worry, it's my mistake...

The MSDS, of course, only mentions what you will find by analysis of the product, not what is put into the product. A considerable amount of KOH goes into the formation of the potassium aminophenolate. I do not know the pH of a solution that originally contained only enough KOH to make the p-aminophenol base soluble as the phenolate, but my attempts to make such a solution have measured in the 12-13 region. The 3% spec is surely an excess, not the total amount put in.

One can make a solution of KOH from K2CO3 and Ca(OH)2 in water. A slight excess of Ca(OH)2 would assure no carbonate in the solution, but perhaps a little of the calcium hydroxide. Any comment?
• 08-29-2009, 09:47 AM
Kirk Keyes
Quote:

Originally Posted by Ian Grant
Shows how much chemistry (& Biochemistry) I've forgotten, I'd just use a pH meter these days :D

Ian

Well, there's a problem there, as it's really hard to measure pH accurately when it gets much above 12.5 or so. You have to start getting special electrodes and the like.

But for MSDS work, it doesn't have to be too precise.
• 08-29-2009, 09:57 AM
Kirk Keyes
Quote:

Originally Posted by gainer
One can make a solution of KOH from K2CO3 and Ca(OH)2 in water. A slight excess of Ca(OH)2 would assure no carbonate in the solution, but perhaps a little of the calcium hydroxide. Any comment?

Well, if you are on desert island or you don't mind calcium in your potassium hydroxide, that's one way.

Industrially, my Hawley's Condensed Chemical Dictionary states that potassium hydroxide is manufactured by the electrolysis of potassium chloride. Then residual sulfur compounds can then be removed by the addition of potassium nitrate to the fused caustic. It can then be further purified by solution in alcohol, filtration, and finally evaporation.
• 08-29-2009, 10:02 AM
Kirk Keyes
Quote:

Originally Posted by gainer
The 3% spec is surely an excess, not the total amount put in.

That's certainly true, as some reacts. And we can calculate how much reacts and how much is excess and figure the sum.
• 08-29-2009, 05:07 PM
Kirk Keyes
As this thread is getting a bit long in the tooth, a new thread with a fresh start has begun at:
http://www.apug.org/forums/forum223/...s-part-ii.html

It would be appreciated if further discussion from this thread continue in Part II.
Thanks!
• 08-29-2009, 05:21 PM
AgX
I already got lost and probably need extra tuition.
• 08-29-2009, 06:00 PM
billtroop
>Bill - are you saying you are suprised that a 3% solution of potassium hydroxide has a pH of 14? If so, here's the way to calculate it.

No, what I mean is that I recall having seen in the past Rodinal packaging which maintained that the pH of the solution was a few units lower, which would indicate a substantially different formula from anything being discussed here. I remember pH 9.8 or something like that ? ? ? It's just something that stuck in my head and could easily be wrong.
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