Molecular weights and water differences

[What About Bob]

Would there be a chart available that would bring together the conversion factors for sodium and potassium as well as for anhydrous, mono, and other differing water weights all into one neat page?

For example I will be putting together a developer that calls for anhydrous potassium carbonate but I only have monohydrated sodium carbonate on hand. Going from anhydrous to mono for sodium, from what I remember, the factor is 1.17, while in the other direction it would be 0.85. The potassium to sodium conversion I am unclear about. I know I could just buy the anhydrous potassium carbonate but if I all ready have the sodium version on hand and if it will work just the same then I would be all set. Unless there is good reason to not use what I have. Like some kind of benefit to using the potassium version?

The developer in question is toward Crawley's FX-55 developer. I am in the process, no pun intended, of getting a new gram scale that will be set up for two decimal places, for the phenidone-A that I will be ordering.

Until I find a way to safely warm up glycol I will be mixing with the powder way first. I had thought to use a microwave for heating glycol but something in my head was like yeah wait a minute: there is only one and you can't use it because it is for food and also because anything but water could have some kind of chance of creating a boom if not careful. In my case that wouldn't be too hard to do, lol.

 

[Romanko]

As far as I remember my school chemistry you will need to recalculate the conversion ratio for every chemical you use. I saw a table like this in one of old books but it will take ages to find it again.

I dissolved phenidone in glycol once and I don't remember having any problems with this. A water bath is probably all you need to warm up your glycol to 50 or 60 degrees Celsius. If you don't go for very high concentration this should work.

 

[koraks]

The developer in question is toward Crawley's FX-55 developer

If you follow the formula here: http://www.pictorialplanet.com/advanced_photography/fx-55.html
you'll find that they also list the conversion factor from potassium to sodium carbonate:

* For Sodium carbonate anhydrous use 15.4g

You can then convert that to monohydrate or decahydrate as you prefer.

As to the actual question you asked: you can fairly easily make this kind of chart yourself in e.g. Excel. The whole 'trick' is nothing more than looking up the molar mass of the atoms in the molecules and adding them all up. E.g. sodium carbonate monohydrate = Na2CO3.H2O =

• 2x Na; Na = 2x 23g/mol = 46g/mol
• 1x C = 1x 12g/mol = 12g/mol
• 3x O = 3x 16g/mol = 48g/mol
• 2x H = 2x 1g/mol = 2g/mol
• 1x O = 1x 16g/mol = 16g/mol
• Total = 46 + 12 + 48 + 2 + 16 = 124g/mol

You can do the same for any other compound you want and then determine the conversion factors. Use e.g. a VLOOKUP for the molar mass.

Try it out; it's not very difficult. It's a nice puzzle and maybe nicer to figure this one out yourself instead of relying on a ready-made solution. That way you'll actually understand what's going on, which is not terribly difficult in this case, and the knowledge will serve you well!

 

[What About Bob]

Thanks, Koraks. This is simple!

KBr:
1X K = 39g/mol
1X Br = 80g/mol
Total = 39 + 80 = 119g/mol

Benzene:
6x C = 72g/mol
6x H = 6g/mol
Total = 72 + 6 = 78g/mol

Sodium Thiosulfate:
2X Na = 46g/mol
2x S = 64g/mol
3x O = 48g/mol
Total = 46 + 64 + 48 = 158g/mol

Added:
Sodium Thiosulfate:
2X Na = 46g/mol
2x S = 64g/mol
3x O = 48g/mol

pentahydrate?
2x5 H = 10g/mol
1x5 O = 80g/mol

Total = 46 + 64 + 48 +10 + 80 + 248g/mol

This is fun.

I don't have MS excel but I do have Libreoffice Calc. Would this suffice?

 

[koraks]

You got it! Excellent!

I don't have MS excel but I do have Libreoffice Calc. Would this suffice?

Yes, definitely, or Numbers of Mac. Any basic (or advanced) spreadsheet app will work for this.

 

[lamerko]

It might be worth mentioning one more thing - solubility before and after conversion. Usually potassium compounds have better solubility and are preferred for concentrates. And vice versa - it may turn out that you will not be able to dissolve the given amount after conversion and replacement.

 

[fgorga]

One can certainly use a spreadsheet to calculate formula (molecular) weights as mentioned above.

However, sometimes it is easier to let someone else do the 'programming'...

Molecular Weight Calculator

Calculate the molecular weight of a formula. Input the molecular formula and the weight is calculated. Also provides the atomic number, element name, base atomic weight and formula weight for the calcutated molecular formula.

www.calculatorsoup.com

There are many other similar on-line calculators out there. This just happens to be the one I have bookmarked.

Once you have formula weights for the compounds you are interested in then it is all a matter of ratios.

 

[Vaughn]

It might be worth mentioning one more thing - solubility before and after conversion. Usually potassium compounds have better solubility and are preferred for concentrates. And vice versa - it may turn out that you will not be able to dissolve the given amount after conversion and replacement.

FWIW...Ammonium dichromate is more solulible than potassium dichromate.

 

[koraks]

FWIW...Ammonium dichromate is more solulible than potassium dichromate.

Solubility limits w.r.t. the popular cations goes ammonium - potassium - sodium, in decreasing order. Facility of dissolution follows in general terms the same pattern.

 

[Vaughn]

Solubility limits w.r.t. the popular cations goes ammonium - potassium - sodium, in decreasing order. Facility of dissolution follows in general terms the same pattern.

Thanks...Where would Calcium fit into that? (Calcium vs Sodium carbonate, for example)?

 

[koraks]

All the way at the bottom - that's why you get scale in your shower cabin. This is mostly calcium carbonate, which has a very low solubility limit!

 

[Vaughn]

Thanks -- I'll stick with Sodium carbonate for reducing carbon prints!

 

[Doremus Scudder]

There are conversion tables for anhydrous vs various hydrates for many common darkroom chemicals in the Darkroom Cookbook.

Doremus

 

[What About Bob]

@lamerko: I will keep this in mind, in relation to concentrates. Thanks! To err on safety I did order the potassium carbonate and will go with that when making the FX-55 I ordered some extra chemistry that I may not need right now but it's good to prepare for later on.

@fgorga: That is neat. Bookmarked, thanks!

@Vaughn: Recently I was reading an article on lime and Lye: http://www.cavemanchemistry.com/oldcave/projects/lime/

The following paragraph about a 3rd of the way down:
"The main disadvantage of lime is its limited solubility. Whereas sodium carbonate has a solubility of 22 g/100 mL and potassium carbonate has a solubility of 147 g/100 mL (!), the solubility of calcium hydroxide is only 0.19 g/100 mL. Even worse, most calcium compounds are even less soluble, e.g. calcium carbonate has a solubility of only 0.001 g/100 mL. So many anions present in the solution may form insoluble precipitates in limewater. In particular, soap contains anions which, in the presence of calcium, form the insoluble precipitate commonly known as "soap scum.""

@Doremus Scudder: Thanks, Doremus. Getting right on it.


I'm going to study up more on chemistry. This thread has been a great step.

 

[lamerko]

Calcium carbonate is a strange compound - you can get a much higher solubility depending on the conditions or at high temperatures 60-80 degrees Celsius - it will precipitate. In fact, one of the methods to reduce water hardness is precisely by boiling...