Properties of chemicals used in photochemistry (pH calculation)

[bnxvs]

I propose to share data on the properties of substances, incl. the values of the constants of acidity and basicity. This data is difficult to find in one place on the Internet.
Here are some of the data I'm using ... comments and corrections will be grateful if there are any inaccuracies:

Name -- pKa/pKb -- Mw (g/M)
Hydroquinone -- pka=10.35 -- 110,11
Borax decahydrate -- pkb=4.76 -- 381,43
Potassium sulphite -- pkb=6.81 -- 158,26
Boric acid -- pka1=9.24 pka2=12.74 pka3=13.8 -- 61,83
TEA (triethanolamine) -- pKb=6.24 -- 149,19
Cathehol -- pka=5.18 -- 110,11
Na3PO4 (trisodium phosphate) -- pka=12 -- 163,94
4-Hydroxyphenylglycine (glycine-photo) -- pka1=1.74 pka2=8.57 -- 167,16
K2CO3 (potassium carbonate) -- pkb=3.68 -- 138,205

 

[bnxvs]

TEA, DEA & MEA pH data

 

[Rudeofus]

Several of the compounds you listed have more than one pKa value. Potassium Carbonate and Potassium Sulfite are rarely used in photo chemistry because of their lower pKa value at 3.68 and 6.81, but rather for their higher pKa values. The pKa value sets of Borax and Boric Acid should be merged into one. The pKa value you listed for Catechol appears way off.

These tables are really a lot of work, and they are very error prone, which means we will frequently have to make additions and corrections. I don't think, that a forum thread is a good format to reflect this. I suggest we start some wiki or something like this. I will happily< submit my set of data once a suitable platform is created.

 

[bnxvs]

Unfortunately, very often you have to come across such a position - "I will do it if someone makes a platform for me" ))) That is why I created this topic. No one will stop us from making any additions and changes, if necessary. And the one who is interested in it and needs, will read the thread to the end, I suppose.
p.s. Potassium sulfite and carbonate are quite actively used, believe me. For example, I use potassium salts in almost 50% of cases because of their good solubility.

 

[Rudeofus]

p.s. Potassium sulfite and carbonate are quite actively used, believe me. For example, I use potassium salts in almost 50% of cases because of their good solubility.

I did not write, that these two compounds are not used. When these two compounds are used, they are typically used at high pH. Take Potassium Carbonate, it is typically used in developers to set pH somewhere between 9 and 11. It has two pKa numbers: 6.3 and 10.32. Only the latter number is relevant for photographic developers. Listing pKa = 3.68 is mostly pointless, since very few photographic liquids operate at this pH. Also, if you start with carbonate and drop pH below 5, there will be lots of Carbon Dioxide dissolved in water, which means the relevant pKa will be 6.3, not 3.68.

 

[bnxvs]

Solubility of hydroquinone

 

[alanrockwood]

As luck would have it, within the last day or two I found a webpage with a nice buffer calculator for carbonate/bicarbonate buffers. It covers a range of pH values and buffer concentrations.

https://www.aatbio.com/resources/buffer-preparations-and-recipes/carbonate-bicarbonate-buffer-ph-9-2-to-10-6#:~:text=Carbonate-bicarbonate buffer is used,prepare, with excellent shelf life.&text=Add 1.05 g of Sodium bicarbonate to the solution.


Also the pKa of para aminophenol is 5.48 for the amino group and 10.30 for the phenol group. It is that second number that is mostly relevant for photographic developers. By coincidence that is almost the same pKa (10.33) as the release of H+ from the bicarbonate group.

The two pKa values for para aminophenol also gives a rough idea of what the pH range is for minimum solubility. If pH is much higher than 5.5 and much lower than 10.3 then para aminophenol will be less soluble than if the pH is outside of that range. The reason is para aminophenol is strongly ionized outside of that pH range and therefore more soluble in water, whereas well inside of that pH range para aminophenol exists in a mostly unionized form and is therefore less soluble.

 

[bnxvs]

As luck would have it, within the last day or two I found a webpage with a nice buffer calculator for carbonate/bicarbonate buffers. It covers a range of pH values and buffer concentrations.

https://www.aatbio.com/resources/buffer-preparations-and-recipes/carbonate-bicarbonate-buffer-ph-9-2-to-10-6#:~:text=Carbonate-bicarbonate buffer is used,prepare, with excellent shelf life.&text=Add 1.05 g of Sodium bicarbonate to the solution.


Also the pKa of para aminophenol is 5.48 for the amino group and 10.30 for the phenol group. It is that second number that is mostly relevant for photographic developers. By coincidence that is almost the same pKa (10.33) as the release of H+ from the bicarbonate group.

The two pKa values for para aminophenol also gives a rough idea of what the pH range is for minimum solubility. If pH is much higher than 5.5 and much lower than 10.3 then para aminophenol will be less soluble than if the pH is outside of that range. The reason is para aminophenol is strongly ionized outside of that pH range and therefore more soluble in water, whereas well inside of that pH range para aminophenol exists in a mostly unionized form and is therefore less soluble.

Thank you!

 

[bnxvs]

Off-topic
The method of restoring old paraoxyphenylglycine (glycine-photo) - is further referred to as POPG.
USSR patent No. 43004
10 kg of POPG is dissolved in 130 l of water and 4 kg of a 25% ammonia solution.The resulting solution is brought to a boil and a small amount of activated carbon and hydrosulfite (aqueous bisulfite solution) is added to it, after which the mixture is boiled for 10-15 minutes.
The mixture is then filtered. A 30-40% sodium bisulfite solution is added to the resulting solution. In this case, white shiny crystals of pure POPG fall out. The crystals are squeezed out in a centrifuge or filtered off, washed with a small amount of distilled water and then with 5-10% bisulfite solution. Then they are dried.
The result is about 8.5 kg of pure POFG.
The obtained POFG does not oxidize in air and retains its white color.

 

[bnxvs]

About 2000 names of chemical substances. Excel file. https://mega.nz/file/QwdWQBQK#0As4ZoAhbWdFb9fDjPDZcAovBMb81kOXFn4TWTWqSS8