Kodalk, what is it/replacements

[titrisol]

What is the composition of KODALK?
Any ways to replace it?

Is it borax/boric acid?

 

[ann]

Balanced Alkali. Which is also know as sodium metaborate. Anchell"s Darkroom Cookbook indicates the substitution can be weight for weight.


Sodium Carbonate can be used as a substitute. However, it is not weight for weight.

 

[titrisol]

Na-Metaborate (Na-BO2)
That gave me better hits, like this one:

Photobinbook.com
"Michael Gudzinowicz" <bg174@F...> wrote on Dec 22, 2000
I've included the proportions required to make 100 g metaborate. The Kodalk
Balanced Alkali MSDS on the EKC website indicates that it is composed of
sodium metaborate octahydrate.

Kodak probably had a patent for a fusion process to make the compound,
but you don't want to go off in that direction, since you want the
product in solution, and not as a crystaline solid.

What you need to know is:

100 g Kodalk (sodium metaborate octahydrate) == 40.5 g borax + 9.53 g NaOH

How to get there is outlined below:

Sodium metaborate (NaBO2) undergoes hydrolysis upon solution to give sodium
hydroxide and boric acid (a very weak acid):

NaB02 + 2 H2O <->>> Na+ + OH- + H3BO3

Borax, the decahydrate of sodium tetraborate (Na2B4O7), may be thought of
as being composed of two metaborate molecules and one of boric anhydride:

Na2B4O7 == 2 NaBO2 + B2O3

Upon dissolution, the products of metaborate from borax are as above, but
multiplied by two below:

2 NaB02 + 4 H2O <->>> 2 Na+ + 2 OH- + 2 H3BO3

The boric anhydride is hydrolyzed to boric acid:

B2O3 + 3 H2O <->>> 2 H3BO3

Overall, the products are:

Na2B4O7 + 7 H2O <->>> 2 Na+ + 2 OH- + 4 H3BO3

If one were to add two mol NaOH to each sodium tetraborate, the products
would be equivalent to those derived from metaborate:

Na2B4O7 + 7 H2O + 2 NaOH <->>> 4 Na+ + 4 OH- + 4 H3BO3

4 NaBO2 + 8 H2O <->>> 4 Na+ + 4 OH- + 4 H3BO3

Molecular weights:

Borax (sodium tetraborate decahydrate) 381.42
Sodium metaborate octahydrate 209.82
Sodium hydroxide 40.01

Since two mols of NaOH are required per tetraborate:

381.42 g borax + 80.02 g NaOH == 839.2 g metaborate octahydrate
(all in solution)

Or to make a quantity equivalent to 100 g sodium metaborate octahydrate:

100 g sodium metaborate tetrahydrate == 40.5 g borax + 9.53 g NaOH

Thanks ANN!!!

 

[Helen B]

Here's Ryuji Suzuki's version of the story, and a bit more of a similar story from 20 Mule Team themselves.

Best,
Helen

 

[titrisol]

soo basically the formula i found would be a double concentration of kodalk?

 

[Helen B]

I'm waiting to hear what others have to say. I recall reading a post by Patrick that gave similar proportions as RS, but it would be better coming from him than me.

 

[gainer]

I suppose you are referring to this Patrick.

Sodium metaborate 4 mol becomes sodium metaborate 8 mol at temperatures above about 53 C. Everything doubles, not just the water of crystallization. IOW, sodium metaborate 8 mol = 2(sodium metaborate 4 mol). This is according to the Arm & Hammer web site. Thus, if you start with the 4 mol at 20 C, you will have the same weight of the 8 mol at 60 C.

The proper way to make the eqyivalent of 100 g of it it is with 69 g borax and 14.5 g lye. Borax is the official name for Na2B4O7.7(H2O), the stuff you get at the supermarket.

 

[ThomHarrop]

When we run out at school we use 20 Muleteam borax from the grocery store.

 

[dancqu]

What is the composition of KODALK?
Any ways to replace it? Is it borax/boric acid?

There are three oxygen acids of boron; ortho, meta, and tetra.
IIRC, the formulas are in order; H3BO3, HBO2, and H2B4O7.
You can see by the formulas that the acids are progressively
dryer. That has to do with the temperature at which they are
formed. At a high temperature all that's left is B2O3, the oxide.

To 'hydrate' the sodium salt of the tetra acid, borax, sodium
hydroxide is used. If you had tetraboric acid and wished the
meta you would add hydrogen hydroxide, water.

Lye is very hygroscopic. Excess of it will produce the ortho salt.
I'd suggest having the metaborate on hand. Dan

 

[Deckled Edge]

Sodium metaborate, $16/kg at B&S. When I ran out of Kodalk, I ordered from B&S and it seems fine, though I have no way of differentiating heptahydrates from octahydrates. Results is results.

 

[gainer]

What is the composition of KODALK?
Any ways to replace it?

Is it borax/boric acid?

Yes, you can replace it, and no, it is not borax+boric acid. I refer you to www.borax.com. Borax is the accepted common name for Na2B4O7.7H2O. Kodalk is either NaBO2.4H2O or Na2B2O4.8H2O, take your pick. They are equivalent. Above 53 C, NaBO2.4H2O becomes Na2B2O4.8H2O in solution. The mixture of borax and lye I gave above approximates that closely enough for government work.

Just plain borax will not achieve pH = 10 no matter how much you dissolve.

 

[titrisol]

OK, so is a buffered pH 10 alkali.
Perfect, borax/NaOH is what I was looking for.
Thanks guys!

 

[dancqu]

Yes, you can replace it, and no, it is not borax+boric acid.
I refer you to www.borax.com. Borax is the accepted
common name for Na2B4O7.7H2O.
Above 53 C, NaBO2.4H2O becomes Na2B2O4.8H2O in solution.

Na2B4O7.10H2O; a decahydrate. That 10H2O, as some know, is the
water of crystallization.

Vice versa. Above 53 C, NaBO2.8H2O becomes Na2B2O4.4H2O in solution.
Dehydration occures as the temperature rises. Again those
H2Os are waters of crystallization.

From my reading at www.borax.com both hydrates are stable.
The 4 Mole has a little more ph per pound. Dan

 

[gainer]

Serves me right for not looking it up. Borax is the decahydrate. There is a heptahydrate of sodium carbonate, but it doesn't seem to have a common name. Its decahydrate is commonly known as washing soda. Maybe the fact that my brain's hard drive is 77 years old has something to do with it. This is the age when one may not only forget things, but also forget that he forgot them.

 

[gainer]

"From my reading at www.borax.com both hydrates are stable.
The 4 Mole has a little more ph per pound. Dan"

The table I saw at www.borax.com showed a gradual change of pH with concentration and a transition from 4 mol to 8 mol above 53 C. I can't see how that jibes with what you saw. The molecular weight of the 8 mol is exactly twice that of the 4 mol, but a given weight of either one contains the same number of molecules. I don't think you can crystallize the 8 mol from a solution below 53 C. So far as I can see, the transition is reversible. I don't think there exists a solid NaBo2.8H2O.

 

[gainer]

I should have said "a given weight of either compound contains the same number of atoms of Na, B, H and O."

 

[dancqu]

"From my reading at www.borax.com both hydrates are stable.
The 4 Mole has a little more ph per pound. Dan"

I don't think there exists a solid NaBo2.8H2O.

At the borax site choose, products and services, then, our products.
VIEW both the 4 and 8 mole technical info. Stability and solubility
are of most interest.

Correct. There is no metaborate as you've mentioned above. There
is though Na2B2O4.8H2O which will crystallize as such from solution
at temperatures below 53 C. Above that temperature crystalls of
Na2B2O4.4H2O will form.

It's likely they ship both the 4 and 8 mole products. NaBO2 and
Na2B2O4 are used interchangeably. I could only guess why that
is so.

 

[Helen B]

'At the borax site choose, products and services, then, our products.
VIEW both the 4 and 8 mole technical info. Stability and solubility
are of most interest.'

...or just click on the link I gave at the start of this discussion to go there directly, but may as well give again here:

4 Mol

8 Mol

 

[gainer]

Anyway you look at these sites, the number of atoms of Na, B, H, and O that you get by weighing out a gram is the same for either the 4 Mol or the 8 Mol. In solution the water of crystallization just increases the amount of water.

I doubt that the chance of getting anhydrous NaBO2 when you order sodium metaborate are very good. I could be wrong. It seems I have been wrong a lot lately.

I had the temperature ranges backward.