Sodium Carbonate replacement

I'm re-examining many of my long time assumptions:

When using Arm & Hammer washing soda in place of Sodium carbonate is it used as a mono-hydrate or anhydrous?

TIA,

anyhydrous

i think.

Wayne said:

i think.

Click to expand...

OOP'S, you're in the same boat as I am....

Everything I've been able to find online indicates that the monohydrate is the most stable form---the others tend to change into it over time in normal storage conditions. You can get it in the anhydrous form (e.g., from the Formulary), but in a cardboard washing-soda box it would pick up water molecules from the air and turn into monohydrate even if it didn't start that way.

Disclaimer: I'm repeating what I've read, so I'm only as sure as my trust in my sources (which, however, include some of the Actual Chemists here on APUG).

-NT

This states that Arm & Hammer Washing Soda is 85% sodium carbonate, 15% water, so it’s probably not anhydrous.

http://hpd.nlm.nih.gov/cgi-bin/household/brands?tbl=brands&id=3005022

The monohydrate form has a mass of about 124g/mol, while the anhydrous form is about 106g/mol.

(106g/mol)/(124g/mol) = 0.85, which is about the stated percentage of sodium carbonate in Arm & Hammer Washing Soda.

Based on this, my estimate is that it’s the monohydrate form.

Perhaps one of our experienced chemists will contribute an authoritative answer.

i suppose you could force out some of the water
by heating it up in your oven on a cookie sheet
the same way you would "convert" baking soda into
sodium carbonate.

It is the monohydrate form and is essentially technical grade and contains a small amount of sodium chloride and a smaller amount of iron. It is good enough for paper developers but not for ascorbate developers where the iron may be a problem.

A purer form can be obtained by heating Arm & Hammer Bicarbonate of Soda which is USP grade. I would recommend doing this for developers such as Xtol substitutes and for the Beutler formula.