How much NA3po4 ....molar masses, it's all the same?

[fr3n0z]

Hi, i think i have a problem with my sodium phosphate solution. I am dosing but it is not rising. I've just dosed the equivalent of 1mg/l and the hanna checker after 1h reads 0.08ppm (from 0.00 before dosing). In just one hour i think it should be more...right?

I am using sodium phosphate bought here in france...

Formule	Na3PO4
Masse molaire2	163,940 7 ± 0,001 2 g/mol Na 42,07 %, O 39,04 %, P 18,89 %,

That means that the PO4 part is about 57,93% and the other 42% is salt? So it is right to think that 10grams of na3po4 in 1 liter rodi should raise po4 in 100l by 0.058ppm?

 

[Miami Reef]

Are you taking into account that calcium carbonate surfaces adsorb a lot of phosphates until they reach equilibrium?

 

[chipmunkofdoom2]

Dodecahydrate means there are 12 water molecules. So the actual formula is something like Na3PO4 12H2O. You'll need to add the weight of water (18.015 * 12) to your calculations.

 

[fr3n0z]

Are you taking into account that calcium carbonate surfaces adsorb a lot of phosphates until they reach equilibrium?

yes randy already told me that po4 they could be going to rocks, etc BUT i tought that after 1h i should still see lot's of it (1ppm dosed and 0.08 on checker it does not seems right to my noob eye)

 

[fr3n0z]

Dodecahydrate means there are 12 water molecules. So the actual formula is something like Na3PO4 12H2O. You'll need to add the weight of water (18.015 * 12) to your calculations.

i am sorry, i know next to nothing in chemistry. could you hint me on the correct math i should apply pls?

 

[chipmunkofdoom2]

i am sorry, i know next to nothing in chemistry. could you hint me on the correct math i should apply pls?

Sure. 163.94 is the molar mass of Na3PO4. Your compound is dodecahydrate, which means it has 12 water molecules. The weight of water is 18.015. So 12 x 18.015 = 216.18 of water weight. 216.18 + 163.94 = 380.12 total.

PO4 has a weight of 94.971, so 94.971 / 380.12 = 24.98% PO4 by weight.

So 10g of your solution in 1 liter makes a solution of 2.498 g/L PO4, or 2498 mg/L.

By my calculation, you need to dose 26.65 100 ml per 100 liters to raise phosphate by 2.49 mg/L (2.49 ppm).

Try dosing your solution to a batch of freshly-mixed seawater. New saltwater should have 0 phosphate, which will give you a better idea of your solution's strength.

EDIT: sorry, originally said 26.65 ml/100 liters = 2.49 mg/L. I had my calculations set to gallons.

 

[fr3n0z]

Sure. 163.94 is the molar mass of Na3PO4. Your compound is dodecahydrate, which means it has 12 water molecules. The weight of water is 18.015. So 12 x 18.015 = 216.18 of water weight. 216.18 + 163.94 = 380.12 total.

PO4 has a weight of 94.971, so 94.971 / 380.12 = 24.98% PO4 by weight.

So 10g of your solution in 1 liter makes a solution of 2.498 g/L PO4, or 2498 mg/L.

By my calculation, you need to dose 26.65 ml per 100 liters to raise phosphate by 1 mg/L (1 ppm).

Try dosing your solution to a batch of freshly-mixed seawater. New saltwater should have 0 phosphate, which will give you a better idea of your solution's strength.

Thanks a lot, is gettin more clear why it seems always to underdose heavily.

 

[chipmunkofdoom2]

Thanks a lot, is gettin more clear why it seems always to underdose heavily.

You're welcome! I had the same issue when I started dosing PO4.

I also just want to point out that I made some errors in my original calculations and have made a few corrections. A dose of 100 mL per 100 liters gives a final concentration of 2.49 mg/L (ppm).

 

[fr3n0z]

Sure. 163.94 is the molar mass of Na3PO4. Your compound is dodecahydrate, which means it has 12 water molecules. The weight of water is 18.015. So 12 x 18.015 = 216.18 of water weight. 216.18 + 163.94 = 380.12 total.

PO4 has a weight of 94.971, so 94.971 / 380.12 = 24.98% PO4 by weight.

So 10g of your solution in 1 liter makes a solution of 2.498 g/L PO4, or 2498 mg/L.

By my calculation, you need to dose 26.65 100 ml per 100 liters to raise phosphate by 2.49 mg/L (2.49 ppm).

Try dosing your solution to a batch of freshly-mixed seawater. New saltwater should have 0 phosphate, which will give you a better idea of your solution's strength.

EDIT: sorry, originally said 26.65 ml/100 liters = 2.49 mg/L. I had my calculations set to gallons.

i was just banging my head againt that ...i could not get around why with your calculation was even weaker than original dosing ...now is better, thanks

 

[chipmunkofdoom2]

i was just banging my head againt that ...i could not get around why with your calculation was even weaker than original dosing ...now is better, thanks

Yes sorry about that. My equations are set up to calculate dosing ml in gallons, and I think something happened with the unit conversions.

The final edit should be correct. Dosing 100 ml of a 2,498 mg/L solution should yield a 2.49 mg/L (ppm) increase in concentration in 100L.

 

[fr3n0z]

Yes sorry about that. My equations are set up to calculate dosing ml in gallons, and I think something happened with the unit conversions.

The final edit should be correct. Dosing 100 ml of a 2,498 mg/L solution should yield a 2.49 mg/L (ppm) increase in concentration in 100L.

yep spot on...and following your calculation, with my initial dosing of 4grams for 1lt of rodi it gives me 0.12ppm for 10ml of po4 while originally i was thinking to dose 0.5ppm . Suddenly my hanna checker results of 0.08ppm 1hr after dosing have much more sense.