Hello all,
If I remember correctly from Gen Chem, the discussion of buffers began with something called "The Common Ion Effect." For instance, if a simple buffer is prepared (say sodium acetate/acetic acid), there is a common ion once the ions are disassociated (in this case, the common ion is acetate).
However, I was seeking help today in my research lab, and a technician told me that I can make a "phosphate buffer and titrate it with HBr" for the current project on which I am working. And I thought, well, yeah, if I need to lower pH I can always add acid, but... in that case, where's the common ion? Wouldn't I want to use something like monosodium phosphate and phosphoric acid?
I understand that the H+ generated from the disassociation of HBr in water would cause a decrease in pH (which is what I need to do)--that's pretty obvious. But, I thought the whole point of common ions was to make use of the equilibrium involved in weak acid disassociations. By making use of the equilibrium, the common ion can "suck up" or donate protons as necessary.
Am I missing something here?
thanks,
kirsch