[born2dive00]

I am a social science teacher, not a chemist, and I have been trying to figure this out accurately for 4 days now without success. I could use a helping hand.

Ok so here is what I am trying to figure out. I have total of 2177.737394 mg of phosphorus in 18927.1ml
Now in the same 18927.1ml I also have 1921.532995 of sodium.

Now I know that the 2 chemicals that are accounting for the phosphorus and sodium are Phosphoric acid, and Sodium Hydroxide.

So when I take the "elemental phosphorus" of 2177.737394mg and divide that by the 31.6074% i get 6889.960561mg of 100% phosphoric acid, or 8105.835954mg of 85% phosphoric acid.      

Now when I do the same for the "elemental Sodium" of 1921.532995mg, and divide that by 57.4785% I get 3343.046522mg of sodium hydroxide @100%

Now we have 18972.1ml of water with 6889.960561mg of 100% phosphoric acid in it. The final ph of the solution MUST BE 3.05pH,

First question is, how much sodium hydroxide do I have to add to the Phosphoric acid solution to get a pH of 3.05?
2nd. I know that at a pH of 3.05 I get the species of H3po4, and H2PO4, so how much of each is in the solution.
3rd. How much Trisodium Phosphate and or Di Sodium phosphate is formed when adding the sodium hydroxide to the phosphoric acid.
4th. How much many mg of sodium is left over


Please show math step by step as I need to put this into a excel sheet for future calculations.

Thank you all
Brad

[Borek]

Generally speaking this is not trivial and there are no simple formulas to help you with. First step is to convert your numbers to molar concentrations of acid and base, then plug them into the equation 11.16 from here: http://www.chembuddy.com/?left=pH-calculation&right=pH-salt-solution and solve for the H⁺.

I told you using so many digits doesn't make sense, looks like you have ignored it