Sodium Metaborate from Borax and Lye
I'm looking to make Sodium Metaborate from Borax and Lye but am confused as to the amounts to be used. The Darkroom Cookbook states that 100g of Sodium Metaborate = 9.5g Lye + 45.5g Borax while I find other references on the Internet that state that 100g of Sodium Metaborate = 14.5g Lye + 69g Borax. So with myself being a non-chemist and just a recipe follower, which one is right?
Practical, not theoretical apporach
I am pretty sure that I saved this from a Pat Gainer post.
Anyways - away we go...
The biggest problem I have faced when mixing metaborate is how pure is the hydroxide? It will absorb humidity and carbonic gas, so it's weight/activity will change as it ages. So, when one mixes the traditional borax/hydroxide formula, the results may vary significantly.
After lots of experimentation, I've devised the following to be able to mix it without the help of a pH meter: The trick is to make a concentrated solution, and mix it in a clear glass container (the concentrate will give visual clues).
25% metaborate solution (as per Michael Gudzinowicz tetrahydrate formula):
Water (room temp - some 20C/68F) - 400cc
Sodium hydroxide - 19g (pour slowly, stirring; usual precautions apply)
Borax - 90g (pour slowly, stir until dissolved, may take a couple of minutes).
Two things may happen:
-If the hydroxide is pure, there will be no borax left and the solution will be clear when stirred. And there will be no metaborate (transparent) crystals in the bottom.
-If the hydroxide is not pure (my case), there will be borax left, the solution will be cloudy when stirred, due to being a mix of dissolved metaborate and un-dissolved borax.
Start to add hydroxide slowly, stirring, 1g a time (or the equivalent in cc of an 20~50% hydroxide solution, easier) until the solution clears
When standing and there are just some borax crystals in the bottom of the solution when not stirred. DO NOT OVERDO.
If the crystals loose the borax whitish look and become kind of transparent (metaborate crystals), you've overdone the hydroxide, and the solution pH will be higher than it should be.
This is like a titration in which borax is the indicator. Let it stand for a couple of minutes (decant) and slowly pour the liquid in another container. Do not pour the crystals that are at the bottom.
Add water to 500cc.
This 25% solution has been mixed more than once, and it passes the basic (ouch!) test - dilute it to 1% and pH is 11.1 (within my pH meter precision). I've frozen it to 0C/32F and left it stand for 2 days at room temp and no crystallization.
Or, you just buy metaborate. It's pretty inexpensive.
I used to make Rodinal, et al, with sod. hydroxide by using Red Devil lye. However, lye has been taken off the shelves in the supermarkets and hardware stores, at least here. I've read where this is due to lye being use in the making of meth.
Anyway, I just buy my Rodinal from Freestyle and my metaborate from Artcraft and save all the hassle of mixing and paying for hazmat shipping fees to get sod. hydroxide.
Lots o lye here though
Yes, sodium hydroxide, a very versatile base. On its own in water it is even a very good paint stripper for cleaning up old metal furniture hardware that has been painted over a zilloin times. I just filter it thougha stainless steel mesh after paint strippling, and still can use it to go on to make soap.
I can still buy red devil lye at my local home hardware. I also do my own superfatted glycerin rich soap, after damaging the skin on my hands many years ago. I did a calculation a while ago, and I could buy bulk lye for the making of 93 lots of soap for the cost of 13 cans of red devil lye. Consequently I now have about 40kg still on hand in a 20L plastic pail (with a well fitting lid) sitting up high on shelf in the basement, well out of reach of curious hands.
The formula I have that I trust, to make a 10% metaborate solution, is:
Originally Posted by MichaelMadio
14.5 grams sodium hydroxide
69 grams borax
Water to make a liter.
If you buy metaborate, don't be confused by the 4 mol-8 mol stuff. You would use the same weight of either in any formula. sodium metaborate 8 mol has twice the molecular weight of the 4 mol. A certain weight of either one has the same number of molecules. One turns into the other at a certain temperature without any change in weight.
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I had this same question...I'm not a chemistry person so, it took me several hours to figure this out but, here's the way I see it....
2NaOH + Na2B4o7(10H2O) + 5H2O <-->> 4NaBO2(4H2O)
2 mols lye + 1 mol Borax (in water) is equivalent to 4 mols Kodalk in water
80g lye + 381.37g Borax (in water) is equivalent to 551.42g Kodalk in water.
divide each of these by 5.5142 and, I beleive, you get the quantities provided by Mr. Gainer.
If you are wondering why the amounts of sodium hydroxide and borax don't add to 100 grams, it's because there is some water of crystallization that comes with the Kodalk or sodium metaborate that you order as such that is supplied with the water needed to make one liter of 10% solution. If you were to remove the water from a liter of the 10% solution by vacuum evaporation, keeping the temperature below about 100 C, the remains would be sodium metaborate as you would purchase it.
Thanks all. Very helpful.
An alternative offering the same ph and still good
buffering is the combination of sodium carbonate and
sodium bicarbonate. The ph of the carbonate is 11.5 +/-
and the bicarbonate 8 +/-. Any ph twixt those two can
be achieved. Dan
I stay away from carbonates because of the calcium and magnesium in my well water. I use rain water or dehymidifier condensate when I must use carbonate. Otherwise, I have no objection to carbonates.
I do think borax has a greater buffer capacity, but a narrower pH range. If I can, I use borax. The metaborate is sometimes convenient if you have it on hand, for neutralizing some components and leaving a considerable quantity of borax equivalent. Borax alone is quite sufficient for a phenidone-sodium ascorbate developer. When the ascorbate is not directly available, the acid can be neutralized by bicarbonate, carbonate or sodium or potassium hydroxide.
I think that with borax, it is easier to calculate how to get a given pH as long as that pH is 9.3.