What is PH of 5% Sodium Carbonate solution?

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

pH, not PH

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.

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

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.

Just a quick clarification:

 

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

 

 

Colin

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

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.

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.

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?

But concentration *is* critical when the sodium carbonate solution is mixed or reacted with other chemicals; if there isn't enough alkalinity present, the developing agent may act as if prematurely exhausted (this is the probable reason for the developer failure that prompted this question) because the pH falls too readily.

 

The suggestion for heating the carbonate powder is a good one -- heat it until it quits losing mass, and you should be at the anhydrous state. Use a regular oven, though; a microwave won't reliably heat the material, especially when it's close to being dry. You could also use a dessicator with concentrated sulfuric acid, but an oven is much easier with a chemical that (like sodium carbonate) can stand strong heating.

 

If you don't want to use the home oven (She Who Must Be Obeyed is likely to object), you could use a saucepan with a tight lid (to prevent loss of the powder, not to keep steam in); same drill, heat until no more weight is lost. You will need to agitate the contents from time to time; just take care not to lose powder when you do, or you'll fail to reach constant weight due to losses.

"But concentration *is* critical when the sodium carbonate solution is mixed or reacted

with other chemicals; if there isn't enough alkalinity present, the developing agent may act

as if prematurely exhausted (this is the probable reason for the developer failure that

prompted this question) because the pH falls too readily. "

 

Yes, it often happens that a certain amount of the carbonate is used to neutralize something else, and the remainder establishes the net pH. Further, the action of development may reduce pH. So, pH of a solution is not simply as one could calculate from concentration of carbonate alone.

 

A case in point: if one adds ascorbic acid to a solution of sodium carbonate, the result will be equivalent to a solution of sodium ascorbate and a carbonat-bicarbonate buffer. If the proportions are right, the pH will be as desired.

It is better to dry chemicals in the conventional oven

Set it around 200-250 F (90-120 C) and let them stand there for 2 or 3 hours to realy dry the powdres.

I'm sorry for being so slow in reacting to the advice and valuable information you all offered. Yesterday, I read everything and started detailed responses for each individual post, but it got much too long a reply. Thanks to you folks, I have found several ways to utilize my 15-20 years old sodium carbonate, monohydrated, and will be able to use it to make my old favorite compensating developer: a two bath variation of Tetenal's Neofin Blue as a one shot developer with slow films.

 

Several members suggested using heat to covert what I have to become pure anhydrous sodium carbonate. I find this to be the least complex method and the one I'll adopt. It eliminates testing for pH or worrying about how much water my carbonate absorbed over the years in its EKC brown bottle.

 

I never finished my chemistry class in my senior year of high school. I left school Christmas break 1942 to do defense work in a shipyard till I turned 18, when my inactive enlistment in air cadet program ended and I was called up. I was given a full diploma, but missed most of the chem class. What you folks wrote has enriched my minimal knowledge of chemistry.

 

BTW I tested the Sol B (5% carbonate solution) that I made earlier this month; it's pH 11. I used pH paper with increments of 10.5, 11 and 11.5

 

 

As an experiment, I thought of adding more of my caked sod. carbonate, monohydrated, to my already prepared Solution B, till I reach pH 11.5 Then, shoot two rolls of Efke KB25 with step grey scales under controlled lighting, and outdoor shots under various light conditions. One roll would be devved in home brew Neofin with adjusted Sol B and the other in same home brew, but with newly made anhydrous sod. carbonate (using covered s/s or pyrex pan in oven)in fresh 5% solution as the new Sol B. Both films to be developed for same time, in same tank, same agitation, rinse fixing etc.--one after the other,then compare negs for tonal range. Is it worth doing?

 

Thanks again for everybody's help. I'm so pleased to have found photo.net and be able to tap the rich source of photo information from such able, thoughtful and helpful people- from near and far.

 

Les

<i>As an experiment, I thought of adding more of my caked sod. carbonate, monohydrated, to my already prepared Solution B, till I reach pH 11.5 Then, shoot two rolls of Efke KB25 with step grey scales under controlled lighting, and outdoor shots under various light conditions. One roll would be devved in home brew Neofin with adjusted Sol B and the other in same home brew, but with newly made anhydrous sod. carbonate (using covered s/s or pyrex pan in oven)in fresh 5% solution as the new Sol B. Both films to be developed for same time, in same tank, same agitation, rinse fixing etc.--one after the other,then compare negs for tonal range. Is it worth doing?</i><p>

 

It depends if you just want to know and consider it worth expending the film and time to find out. Photographically, if your interest is in the images, no; it's much simpler to work with known good chemicals (film is cheap; good images aren't). If you want to expand your knowledge (which, IMO, is generally worth doing), and don't mind the price (two rolls of film and a couple hours of work), then it's worth it to you -- and if you do this experiment, please do post the results!