Buffers

Buffers

1. A buffer is a solution that keeps pH constant with small additions of acid or bases

   • Made of a weak acid and its salt that it forms
     • Take HCOOH and HCOONa
       • HCOOH hardly dissociates into HCOO- and H+. So [H+] is small but [HCOOH] is high
         • If you add base then it will react with H+to make water but then equilibrium shifts to replace the reacted H+
           • This way the pH is pretty much constant
       • HCOONa readily dissociates into HCOO- and Na+. So [HCOOH] is high
         • If you add acid the HCOO- mops up the added H+ and makes HCOOH
     • acidic buffer
   • Alkaline Buffers
     • Made from a weak base and its salt
       • Take NH3 and NH4Cl
         • NH3 hardly accepts H+ from water so you get lots of NH3 but not a lot of NH4+ and OH-
           • add acid and the H+ reacts with OH- but equilibrium shifts to replace the reacted OH-
             • This way pH is pretty much constant
         • NH4Cl readily dissociates into NH4+ and Cl- so lots of NH4+
           • If you add alkali the OH- reacts with NH4+ to make NH3 and H2O which hardly dissociates