Sodium Bisulfite > Sodium Metabisulfite

[Bruce Osgood]

I'm mixing a formula that contains 5g sodium bisulfite as a buffer to hydroquione. I don't have bisulfite but I do have metabisulfite. Is this apples and oranges or is there a conversion?

 

[Lowell Huff]

They are the same thing.

 

[juan]

I've used the metabisulfite as a direct gram to gram substitute with no problem. Maybe a chemist can tell us the real story.
juan

 

[Bruce Osgood]

I've used the metabisulfite as a direct gram to gram substitute with no problem. Maybe a chemist can tell us the real story.
juan

Thanks Juan,
I'll go with 1 to 1 until I hear otherwise. Thank you,

 

[Robert Hall]

They are not the same and the ph is different. I would ask Gerald Koch about this.

 

[Ryuji]

Why do you say that? When dissolved in water, metabisulfite forms bisulfite ion and they are the same thing. In amateur darkroom formulae I doubt anyone ever used pure sodium bisulfite in dry form as an ingredient; it's a misnomer.

 

[Ole]

In solution, they're identical.

There's a difference in the crystal structure, but that doesn't matter at all as soon as it's dissolved.

 

[Robert Hall]

Thank you for the clarification. It was my understanding that Metabisulfite had a lower ph, is this not true?

thx

 

[Gerald Koch]

When Kodak sold chemicals a mixture of sodium bisulfite and sodium metabisulfite was sold as sodium bisulfite. If you look at the MSDS for sodium bisulfite it is listed as 58 - 99% sodium bisulfite and 0 - 42% sodium metabisulfite. Pure sodium bisulfite is sold as a 40 - 45% solution rather than as a solid.

Kodak recommended using the same amount regardless of which chemical the formula mentioned.

 

[Bruce Osgood]

..............

Kodak recommended using the same amount regardless of which chemical the formula mentioned.

Works for me. Thanks to all who contributed.

 

[dancqu]

It was my understanding that Metabisulfite
had a lower ph, is this not true?

There is no metabisulfite in solution. None we be
brewing. At crystallization two bisulfites join loosing
a molecule of water; so the meta. In solution the meta
joins with water; so two bisufites. The meta is more
concentrated by one molecule of water.

Likely there is a source for one and/or the other.
The ph in solution is that of the bisulfite. Dan

 

[Ryuji]

There is no metabisulfite in solution.

Not that it matters a lot in terms of darkroom mixology, but this is simply untrue. In concentrated solution of sodium bisulfite, metabisulfite is present.

 

[dancqu]

Not that it matters ... but this is simply untrue.
In concentrated solution of sodium bisulfite,
metabisulfite is present.

"None we be brewing" I did qualify my statement.
Besides you and I know better. Concentrated
solution or not, as a species metabisulfite
will exist at ten to the minus who knows
how many zeros. Dan