[born2dive00]

Ok I finished my ph calculator which is able to take the species curves of an entered pH and tell you how much of acid and the base you will need, for example phosphorus has 3 4 species, at a ph of 4.68 you will have  .29202% of phosphoric acid, 99.40708% of NaH2PO4, .3009% of Na2HPO4, and 0% of Na3PO4. This equates by dividing by 100 the moles of each substance.

I then calculated how much phosphorus in each of the compounds and added all 4 together, and I calculated the amount of sodium for each of the compounds and added them together, then took the known amount of Phosphorus in 100% pure phosphoric acid, and the known amount of the sodium in Sodium hydroxide and calculated out how many mg was needed for each.

I came out with 97.99765776 g/L of Phosphoric acid, and 40.00167933 g/L of sodium hydroxide added to 1 L of water to give me a pH of 4.68.

Now my question is I have found this to be accurate to +/-2.2mg per 1L of solution based solely on the given pH. Is =/- 2.2 mg of a substance significant in most general chemistry given the errors in equipment (scales, glassware) and user error??? should I be worried about this?

The next question is I have been able to get this to work for 1 acid and 1 base, but how does it work when adding additional acid/base. Say i have a calculator for another mixture of Citric acid and sodium hydroxide. can I simply use the calculated H+/ OH- value and add or subtract them from the known value?

In my above example above at a pH of 4.68 with the phosphoric acid and sodium hydroxide I got a calculated H+ value of .001584893, If my citric acid/sodium hydroxide solution had say a H+ value of .001, can I subtract the .001 from the .001584893 which would give me .000584893 remaining, how do I use this to calculate the pH of the new solution of citric phosphoric acid and sodium hydroxide.

My gut thought is to divide .000584893 by 2 then subtract that from the .001584893 which would give me a H+ of 0.001292447 which would mean that the solution would become more base?

Is this correct? Please let me know and thank you
Brad