Na3PO4 math questions

[Johnd651]

So it's been 15 years since I last had to think in molarity and concentration. Had a couple questions about making Na3PO4 solution.

Mw of Na3PO4 is 163.94 g/mol, PO4 is 94.97 g/mol, giving 58%. So it would be 1.72 g of Na3PO4 to yield 1 g of PO4. So 1.72g per 1L would yield 1000 ppm of PO4 solution. Why is everyone using 1.88g instead? Am I missing something?

Using the 1.88g...
I don't have a scale precise enough so I thought about making a 10x mother solution, so 18.8g into 1L diH2O instead of the 1.88g recommended. And then doing a 10x dilution to get the 1090ppm solution. Would that be 100ml of mother solution into 900ml h20 or 100ml into 1000ml h20? (I always got this question wrong in all 4 years of chemistry.) Once i did this, my dilute solution should be the 1090ppm, so to raise 500L 0.03ppm i would add 15 ml of the dilute?

Also is there a shelf life on the mother solution?

 

[EnterName]

Take a look at my linked post, it should answer most of your questions:

DIY Phosphate Dosing Recipe

@Miami Reef do you know if there's any place to get this stuff in person so I don't have to wait for shipping? It will be difficult to source it in person. If you are in a rush, picking up Neophos is good idea. Both work. Neophos might be a bit more expensive by weight, but both get the job done.

www.reef2reef.com

1.88g is probably used by those using disodium phosphate dihydrate (Na2HPO4 • 2H2O), not trisodium phosphate anhydrate (Na3PO4).

If you create a 1L "mother solution" and want to dilute it down to 10% of it's strength you take 100mL which contains 10% of the dissolved reagent and then fill it up to 1000mL with RO/DI.

Example: If 1L mother solution contains 17.3g Na3PO4, 100mL contains 1.73g. Filled up with RO/DI this yields 1.73g/L which is 10% of the mother solution's strength. Think of adding the mother solution as if you are adding the reagent in powdered form. You don't need to worry about the volume you just want the right amount of reagent in the container. Then you bring it up to volume.

I haven't tested the shelf-life, so I'm not sure about that, but I assume there is a limit.

 

[Johnd651]

Take a look at my linked post, it should answer most of your questions:

DIY Phosphate Dosing Recipe

@Miami Reef do you know if there's any place to get this stuff in person so I don't have to wait for shipping? It will be difficult to source it in person. If you are in a rush, picking up Neophos is good idea. Both work. Neophos might be a bit more expensive by weight, but both get the job done.

www.reef2reef.com

1.88g is probably used by those using disodium phosphate dihydrate (Na2HPO4 • 2H2O), not trisodium phosphate anhydrate (Na3PO4).

If you create a 1L "mother solution" and want to dilute it down to 10% of it's strength you take 100mL which contains 10% of the dissolved reagent and then fill it up to 1000mL with RO/DI.

Example: If 1L mother solution contains 17.3g Na3PO4, 100mL contains 1.73g. Filled up with RO/DI this yields 1.73g/L which is 10% of the mother solution's strength. Think of adding the mother solution as if you are adding the reagent in powdered form. You don't need to worry about the volume you just want the right amount of reagent in the container. Then you bring it up to volume.

I haven't tested the shelf-life, so I'm not sure about that, but I assume there is a limit.

The powder part to dilute out is perfect... that clicked.. wish my college profs made that connection.

 

[EnterName]

The powder part to dilute out is perfect... that clicked.. wish my college profs made that connection.

I'm glad I could help. I'm not a chemist though, so always double check the math :)
Happy Reefing!