Potassium carbonate monohydrate?

[kenneth_bruno]

Greetings,

 

Is potassium monohydrate still produced??? Older glycin film developer

formulas call for monohydrate and it is next to impossible to find. Hubl

paste and FX-2 call for sesquihydrate which can be found though quite

expensive. Question: will using potassium carbonate anhydrous have an impact

on the performance of these developers?

 

My best,

Ken

[patric_dahl_n]

"hydrate" means that the chemical is crystalized with water. "Anhydrous" means that the chemical is water free.

 

It doesn't matter if you use monohydrate or anhydrous Potassium Carbonate. You just have to use less of the anhydrous.

 

If the forumula says "45g Potassium Carbonare Monohydrate", multiply with 0.855 = 38.5g Potassium Carbonate Anhydrous.

[patrick_gainer]

Why would you want to pay more for water you can add yourself? The molecular weight of potassium carbonate is 138.2. 1 molecule of water adds 18. For every 156.2 grams of the monohydrate called for, use 138.2 grams of the anhydrous.

 

My CRC Handbook of Chemistry and Physics does not list a monohydrate, but does list a dihydrate. The trihydrate molecule has 2 molecules of K2CO3 + 3 molecules of water. I don't see a sesquihydrate listed as such, but "sesqui" means 1 1/2, so that must be what is listed as the trihydrate, as it has 1 1/2 molecules of water for each molecule of the carbonate. There is no need to pay extra for that water, either. Its MW is 332.4, of which 276.4 is anhydrous K2CO3, so use 0.832 as much monohydrate as the amount of the sesquicarbonate called for.

[kenneth_bruno]

I do understand that there are water molecules attached in each case (except anyhydrous). My concern is if there will be a difference in the performace of the developer when using the anhydrous form. Huble paste, for example, calls for crystal (sesquihydrate) and the amount needed would cost a small fortune on top of the glycin, so the anhydrous form is obviously much less costly. My understanding is that the crystal form is needed for buffering.

 

Wouldn't the anhydrous eventually pick up water molecules anyway?

 

My best,

Ken

[patrick_gainer]

Exactly so. Which form of hydrated carbonate you start with will make no difference when you disslve it in water. You wind up with potassium, carbonate, H and OH ions. The same number of potassium and carbonate ions can be obtained from any of the forms as shown above. The number of H and OH ions will depend on the size of the container you dissolve them in.