ordloh;41928 said:Really difficult to calculate since CO2 and other acids are variables and go up and down all the time in an aquarium. Can be done with some big assumptions. Assuming your aquarium water is pure water with pH 7 and also assuming that dissociation to H3PO4 and PO4 -3 is negligible (Kb of H2PO4- is 10^-12 and Ka of HPO4 2- is around 10^-13, we don't need to bother with them in the aquarium since the pH is never out of 5-8), adding 5e-5 M of phosphate in the form of KH2PO4 will result in a pH of 5.76
Of course the dissociation is less in an acidic solution, unfortunately CO2 and all the organic acids in our aquariums are weak acids so all the equilibriums will be pushing each other back and forth so it’s really hard to calculate. I might try later but I’m not too keen tbh lol.
Philosophos;41938 said:The fact that I don't know the answer to this question sort of annoys me. Buffering questions pop up all the time and most people are just left shrugging. I'm downloading a textbook that should give some answers; it'll be done by tomorrow. I'm going to do my best to learn some of this, and perhaps write on the subject a little bit.
Philosophos;41958 said:If it were just to play with carbonates for the sake of plants, I wouldn't do it. The fact is that I want a solid understanding of chemistry as it applies to the hobby. I've also got another passion in the hobby besides plants, but not exclusive to plants.
I find my self wanting to spawn apistos that require a pH around 5 for good responses and high viability. I'd like to do this with more precision than leaf litter; phosphoric acid comes to mind as an option. Until I have good command over my pH, I don't want to take on the more advanced species.
ordloh;41959 said:yeah tom you're right, too many assumptions. I'm actually really really bad at analytical chem i failed so hard for 1 minor test that it affected my 3 years of accumulated score lol. Philosophos, do you do it by solving simultaneous equations? I'm not really sure how it's suppose to be done XD
For a system with carbonate and phosphate, i had 9 unknowns : [H][H3PO4][H2PO4][HPO4][PO4][CO2][H2CO3][HCO3][CO3] but only 8 equations, 6 K equations, mass balance and charge balance. omg i hate this so much! and imagine if you have bits of calcium carbonate and iron phosphate in your substrate in equilbrium with your water