EDTA 2Na (disodium salt) - adding to developer, neutralising acid with base

[kozesluk]

although I don't have problems with hard tap water at home I tried to add it to my favourite developer in concentration of 5 g/l of working solution. Well, the negative came out underdeveloped, so I researched more and came to a conclusion, that EDTA and EDTA-2Na are mildly acidic.
As I'm not a chemist in any way and have a very bad knowledge of the pH stuff & so on (and I don't have means of measuring pH in any way)...

well, suppose I want to add EDTA-2Na into a bucket of water and since it is acidic I will put there, say, NaOH to neutralize it - or is this a completely wrong idea?

EDTA-2Na can be written as C10H14N2Na2O8 . 2H2O so the reaction can be written in a this way (1 mol of both substances)

C10H14N2Na2O8 + NaOH + (n)H2O --> C10H13N2Na3O8 + (n+1)H2O

C10H13N2Na3O8 is EDTA-3Na - a trisodium salt which should be pH neutral in solution (depending on its chemical purity I suppose).

can anybody here who understands chemistry better than me help me please?

 

[john_s]

5g in a Litre of working solution seems like a lot. Is your developer working solution a rather dilute one (in which case might be sensitive to the EDTA) or a stronger solution which might be expected to not be so sensitive?

 

[kozesluk]

Koblic MPB - sodium sulphite 16 g/l, borax 8 g/l. weakly buffered, I know (suggested pH around 8,5).
but still - if EDTA.Na2 is acid - can it be neutralized with hydroxide then or not?

 

[Gerald C Koch]

EDTA is an expensive way to sequester calcium in hard water. A cheaper solution would be one of the condensed polyphosphates such as sodium tripolyphosphate, sodium tetraphosphate, or sodium hexametaphosphate (Calgon). These are all close to neutral in pH and work well. Kodal used to sell the latter as Kodak Anticalcium #1.

 

[kozesluk]

well, accidentally, I have a bottle of this stuff at home and it cost me nothing, so...

 

[Роберт]

EDTA you can use to sequester Calcium in hard water (and some other metal ions too) but in most formulaes it's limited till max. 5g/ltr. EDTA-2Na 1% has a pH of approx. 4,5.

EDTA-4Na (Fotoplex 1) 1% (10g/ltr.) has a pH of approx. 11,8. Recommended is normally 2g/ltr.

Best regards,

Роберт

(Reference: Sammlung Fotografischer Rezepte, U. Raffay)