I really just want to make my own phosphate buffers....i use:
Sodium phosphate mono and di (156 and 142g/mol respectively)
i use the general HH equation (pH = pka + log (salt/acid))
where the salt monobasic and acid is dibasic.
Ive worked out the ratio's (i.e for concentration acid + base = 1) and get answers that seem to be corroborated on the net:
i.e for ph 7:
7 = 7.2 + log (1-acid/acid)
acid = 0.613
salt = 1- 0.613 = 0.387
this works with others answers i.e.:
http://www.physicsforums.com/showthread.php?t=163100
(very old post i googled)
using this pka (7.21 ~7.2) you should expect 50:50 for a pH at 7.2 right? well all the table on the net give a 50:50 ratio of mono:di when the desired pH~6.9
which is what happened when i made a solution of ~50:50 i got a pH of 6.8 when i really wanted 7.2!
ANY HELP PLEASE AND THANKYOU! or if you would suggest a chemistry forum?
Merged post follows:
Consecutive posts mergednote: the pKA for sodium phosphate is 7.21
but these tables make it look like the pkA is 6.9 or so. which i cannot back up on the net on pKA tables.
