Does anyone know what these chems are?

vjuliano · May 26, 2021

In the 1982 BJP Annual, for E6 it lists

disodium hydrogen orthophosphate (12H20)
monosodium dihydrogen orthophosphate

as components of the bleach and fix. Does anyone know what these are? Have a CAS number for them? Google doesnt really turn anything up, and Mike Johnson of Artcraft doesnt seem to know what they are either.

I have been struggling with some color issues in my home made E6 attempts so I would like to try the BJP version as they have it written before I try swapping in my own Potassium Ferricyanide bleach or something.

Thanks for any help.

AgX · May 26, 2021

vjuliano said:
disodium hydrogen orthophosphate (12H20)
monosodium dihydrogen orthophosphate.

-) Na2HPO4
-) NaH2PO4

vjuliano · May 26, 2021

So Disodium Phosphate and Monosodium Phosphate. I already have disodium phosphate, so thats good.

Any idea why they used these obscure names instead of the ones se all know and recognize?

GLS · May 26, 2021

vjuliano said:
Any idea why they used these obscure names instead of the ones se all know and recognize?

There can be several reasons. Often it is just historical, or it can be to distinguish it from other isomeric forms of the compound, etc. In this case the prefix "ortho" explicitly distinguishes it from "pyro" forms (i.e. containing a phosphonic anhydride) if you don't have a formula or molecular mass on the label. There are yet more ways it can be referred to; for example depending on the number of metal ions the salt contains it can be monobasic, dibasic or tribasic. And so on.

All part of the wonderful world of chemical nomenclature.

Donald Qualls · May 26, 2021

The hydrogen and dihydrogen phosphates aren't necessarily the same as the phosphates -- just as sodium hydrogen carbonate (more commonly called sodium bicarbonate or baking soda) isn't the same as sodium carbonate (soda ash or washing soda). Typically a difference in pH, buffering capacity, and reactivity.

AgX · May 26, 2021

As GLS already hinted at, what seemingly puzzles the OP is not the Mono- versus Di-Sodium thing (what you very well describe), but that "Ortho" thing.

Donald Qualls · May 26, 2021

Ah. It appears that orthophosphate is a single phosphorus compound, as opposed to polyphosphates that contain more than one phosphorus atom. What we usually think of as sodium phosphates are all orthophosphates, but a chemical vendor might specify this to ensure buyers are confident what they're getting.

vjuliano · May 26, 2021

just to be sure, these are infact Disodium Phosphate and Monosodium Phosphate? I am having enough E6 issues without ordering the wrong chems

Nicholas Lindan · May 26, 2021

And don't forget TSP - Tri Sodium Phosphate. Available at hardware and paint stores for cleaning the grease off kitchen walls and ceilings before repainting.

TSP is a mixture of mono, di and tri forms, with the tri predominating.

I worked for a firm that produced huge optical crystals of KDP - potassium di-hydrogen phospate. https://www.photonics.com/Articles/Cleveland_Crystals_Small_Firm_with_a_Big_Role_in/a30633

AgX · May 26, 2021

vjuliano said:
just to be sure, these are infact Disodium Phosphate and Monosodium Phosphate?

Yes.

Does anyone know what these chems are?

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