Rodinal ph?

[jmcd]

Does anybody know the approximate ph of a solution of Rodinal at dilution 1:25, and 1:50? Just curious.

 

[Jerevan]

I think Ian Grant has said something to the effect that the Ph of undiluted Rodinal is 14, while diluted is should be a bit over 11. If you say "Rodinal" around here, sometimes things get really crazy. Drop Ian a pm.

 

[jmcd]

Thanks, Jerevan. And thanks for the warning about saying, "Rodinal."

Ian Grant wrote:

The pH is around 14 sure, but the actual requirement is the pH of the working dilute solution rather than the concentrate which is given elsewhere as pH 11.55, which I commented on in the first post of the thread.

From this thread: (there was a url link here which no longer exists)

 

[brianmquinn]

If it uses NaOH as the base and it starts at pH14 undiluted then
A 1:10 dilution will be pH13
A 1:100 dilution will be pH12
But why do you care?

 

[jmcd]

brianmquinn wrote: But why do you care?

Well, I said, "just curious." But more specifically, I am curious as how to bring it further towards neutral Ph for disposal, as the "corrosive" warning on the label got me to thinking...

 

[Athiril]

depends on the Rodinal, some would use KOH iirc.

Neverr thought to test it. But I got a pH meter here, and next time I use it I'll give it a measure.

At such dilutions the water pH might influence? The water at my new place is pH ~8.5

Well, I said, "just curious." But more specifically, I am curious as how to bring it further towards neutral Ph for disposal, as the "corrosive" warning on the label got me to thinking...

Well it's aminophenol, sulphite and the NaOH or KOH. Which are used as drain cleaners at far stronger strengths than rodinal dilutions.

 

[hrst]

Well, I said, "just curious." But more specifically, I am curious as how to bring it further towards neutral Ph for disposal, as the "corrosive" warning on the label got me to thinking...

Drain opener uses NaOH or KOH at 5x higher concentration than Rodinal concentrate, having pH at 14 or more, and is meant to be poured into drain. These alkalis are corrosive to skin and some metals such as aluminium, but are not corrosive to materials used in drains.

It's more important to neutralize your stop baths. You can use the developer to do that.

 

[Ian Grant]

If it uses NaOH as the base and it starts at pH14 undiluted then
A 1:10 dilution will be pH13
A 1:100 dilution will be pH12
But why do you care?

The inherent pH comes from the high Potassium Sulphite level as well as a small amount of Hydroxide. This is why the Calbe version R09 with no free Hyrdoxide has a pH of 11.8

This means it's far less corrosive once dilute and should;t cause any problems.

Ian

 

[Gerald C Koch]

If it uses NaOH as the base and it starts at pH14 undiluted then
A 1:10 dilution will be pH13
A 1:100 dilution will be pH12
But why do you care?

This is not really correct. Classic Rodinal contained no free potassium hydroxide. It was conbined with the p-aminophenol to form a phenylate salt. This would lower the pH below that of pure potassium hydroxide. For all intents and purposes the pH of sodium and potassium hydroxide are comparable.

 

[Ian Grant]

This is not really correct. Classic Rodinal contained no free potassium hydroxide. It was conbined with the p-aminophenol to form a phenylate salt. This would lower the pH below that of pure potassium hydroxide. For all intents and purposes the pH of sodium and potassium hydroxide are comparable.

The pre-1964 versions of Rodinal from both Agfa & Orwo contained no free Hydroxide, Calbe (formerly part of Orwo) still make that version R09, although in the last year or two at a slightly higher concentration.

However Agfa changed the formula when they merged with Gevaert and dropped the p-aminophenol level, compensating bu raising the pH with free Hydroxide.

Ian

 

[Gerald C Koch]

The pre-1964 versions of Rodinal from both Agfa & Orwo contained no free Hydroxide, Calbe (formerly part of Orwo) still make that version R09, although in the last year or two at a slightly higher concentration.

However Agfa changed the formula when they merged with Gevaert and dropped the p-aminophenol level, compensating bu raising the pH with free Hydroxide.

Ian

It's difficult to calculate the pH of a solution containing more than one component. As the number of components increases so does the complexity. If we can make assumptions about some of the components then we can reduce the complexity of the calculation. For present day Rodinal with excess potassium hydroxide the pH is determined mainly by the amount of the excess hydroxide.

Hence my use of the term "classic Rodinal". This would yield the simplest case to calculate. Here the phenolate salt is producing the pH. The potassium sulfite present would produce a much lower pH and can be eliminated from the calculation.