Ok I am trying to understand this with a definitive answer. There are 4 parts to this question, and I am no chemist (i have a very very basic understanding of chemistry so please be as simple as possible in the answers)
Part 1
If i understand my readings correctly Trisodium citrate will disassociate X amount of sodium as the PH decreases.
So to start i took water that had a pH of 7.2 and added trisodium citrate to it till it could not dissolve any more 100% saturation the pH measured 8.1
So using this as my starting point, I assume that at a pH of 8.1 i have 100% Na3C6H5O7 with Zero disassociation of any of the sodium would this be correct?
Which scenario is correct
Scenario 1
Ph/ pKa: 6.401 i will have it will have (0 amount of) Na3C6H5O7, and (100%) Na2C6H6O7 as the sodium will disassociate, at pH /pKa 4.76, there is (Zero amount of) Na2C6HO7 and (100%) NaC6H5O7 and at A Ph/pKa of 3.138 (Zero amount of) NaC6HO7 and (100%) C6H5O7 is my assumption correct? OR DO I HAVE THIS IN REVERSE?
Scenario 2
So if the Ph/ pKa: is at 3.138 it will have (0 amount of) Na3C6H5O7, and (100%) Na2C6H6O7, at pH /pKa 4.76, there is (Zero amount of) Na2C6HO7 and (100%) NaC6H5O7, and with a pH/pKa of 6.401 there is (Zero amount of) NaC6HO7 and (100%) C6H5O7 and all the sodium will be disassociated.
My gut reaction is this is opposite of a titration of sodium hydroxide and Citric acid where more disassociation occurs as the pH increases, as this is a salt not an acid.
Part 2. If scenario 1 is correct, at what pH will the Na3C6H5O7 start to dissociate sodium, it would have to have a pH/pKa much lower than the 3.138
Part 3. Assuming Scenario 1 is accurate, How much sodium will dissociate at the following pH of 2.85, 2.90, 2.95, and 3.0 3.05, 3.1? I need a way to calculate what percentage of sodium is dissociated
I know that there is mid points so for example if we take 4.76 and subtract 3.138 we get 1.622 and if we divide that by 2 we get .811 so if we add 3.138 + .811 we would get a pH/pKa of 3.949 so at this point we should have a mixture of 50% NaC6HO7 and 50% C6H5O7. But since it is not linear, and there is a curve as you get closer to the end points, how do i calculate the amount of disassociation at a given pH
Part 4. If I am using say phosphoric acid to adjust the Ph, does the dissacioated sodium combine to form sodium phosphates?
Please let me know
Thank you all for your help.