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What is PH of 5% Sodium Carbonate solution?

Lester Gediman , Jul 25, 2004; 12:59 p.m.

In an earlier thread of mine I questioned using old dry chemicals for home brewing the two bath Neofin Blue. A member responded by suggesting using PH as a means to determine correct amount of anhydrous sodium carbonate to make solution B. As my carbonate was caked and taken in an indeterminate amount of water, I'd like to use the PH index found from someone's freshly mixed Neofin Blue solution B, or could make up a tiny sample and tell me what PH I should match. Solution B is only carbonate and water and Beutler's published notes indicate it's a 5% solution. My metol and sodium sulfite is also old, but meet criteria of color of metol being only light tan, and sulfite pouring easily. I want to improve the way I've been mixing solution B so I can get the results I used to get with fresh chemicals. I have a large quantity of the three chemicals and if they still can be used, I'd like to give it a try. I'll be using the home made Neofin with Efke KB25. I loved the negs I got with Adox KB14 (Efke KB25's antecedent) and Neofin Blue and they still print so well.

I'd appreciate any help or suggestions,

Les

Responses


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The Macman , Jul 25, 2004; 01:24 p.m.

pH, not PH

Patrick Gainer , Jul 25, 2004; 03:01 p.m.

A 10.6% solution should have a pH of about 11.6 according to CRC Handbook. If you make a solution with that pH and dilute it 1:1 you should be close. The old carbonate you have has most likely taken on water which can be removed by heating.

Baking soda from the grocery store is USP sodium bicarbonate. If you heat that until 16 oz. original weight reduces to 12.6 oz. after heating you will have quite pure anhydrous sodium carbonate. Just heat it until it quits evolving gas.

Lester Gediman , Jul 25, 2004; 04:15 p.m.

The Macman , jul 25, 2004; 01:24 p.m. "pH, not PH"

I stand corrected.

Patrick Gainer , jul 25, 2004; 03:01 p.m.

"A 10.6% solution should have a pH of about 11.6 according to CRC Handbook. If you make a solution with that pH and dilute it 1:1 you should be close."

Great! I have pH paper for 11.5 and I'd guess that'll be close enough for jazz.

"The old carbonate you have has most likely taken on water which can be removed by heating."

Can it be heated in a microwave? If so, what container material should I use? Covered or uncovered?

"Baking soda from the grocery store is USP sodium bicarbonate. If you heat that until 16 oz. original weight reduces to 12.6 oz. after heating you will have quite pure anhydrous sodium carbonate. Just heat it until it quits evolving gas"

That's a wonderful tip. How can I tell when it quits evolving gas? Is there a visible clue or sound?

Thanks a million Patrick.

Les

John Stockdale , Jul 25, 2004; 05:39 p.m.

It was many years ago that I did high school chemistry, but I have a vague recollection that the pH of a strong base will not vary much with dilution across this kind of range. In other words, measuring the pH will not be very accurate in determining the amount by which the sodium carbonate has gained water.

If you have a graduated pipette and pH paper that would measure the appropriate pH close to 7, you could do a titration with a known strength of acid. This might be a bit of mucking about, but I'm sure it would give you a more accurate figure, and might be worthwhile if you have quantities of it.

This is just FWIW, and I'm no expert.

Colin Lee , Jul 25, 2004; 06:57 p.m.

Just a quick clarification:

Did you mean sodium carbonate (as it the title of the post) or sodium bicarbonate (which is baking soda)?

Colin

Jorge Oliveira , Jul 25, 2004; 09:09 p.m.

From a paper by Rio Tinto (borax, etc), the pH of a 5% solution of carbonate shall be 11.6

Conrad Hoffman , Jul 25, 2004; 09:13 p.m.

Things get hot in the microwave because they have high electrical loss at that frequency. Water heats very well. Mineral oil not hardly at all. It's generally bad for the microwave if it doesn't have a load, i.e., something it can heat. Powdered chemicals, especially if you're trying to dry them, aren't good candidates unless you prove otherwise, and even then heating will be uneven. I'd stick with a skillet on the stove.

Patrick Gainer , Jul 25, 2004; 11:03 p.m.

I used a stainless steel saucepan with a loose fitting lid. You can start out with the lid off. You will see little geysers of gas which will be CO2 and steam. When you swirl the pan it will feel like it has liquid in it until most of the gas is gone. You will also see powder coming out of the pan and settling everywhere if you don't put the lid on. That, of course, is sodium carbonate. Don't breathe much of it. It will clean the stove top when you wipe it up with a damp cloth.

Ole Tjugen , Jul 26, 2004; 09:31 a.m.

You can't go by pH of a strong alkali - it's about the same in 0.2%, 1%, 5%, 10% and 25%. Close enough that measuring the difference takes 1000's of $ worth of lab equipment.

Fortunately htat also means that the concentration isn't really critical - the H will be the same anyway. Just use enough to survive the use.

Is the Neofin Blue formula published? I have several versions of Willi Beutler's published developers, but none of them are Neofin?


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