Water in soil: Neutralization and Watershed Buffering
Water in Soil: Neutralization and Watershed Buffering
pH of a buffer and buffer capacity Example: For a buffer solution consisting of 0. 1 M acetic acid and o 1M sodium acetate the ph of the solution is 4.75. HAc=h+Ac Ka=LH IAc 1 [HAc] [H]=Ka· HAc] LAc =10-470.1 4.75 f an amount of hydrochloric acid, equivalent to 10% of the acetate present, is added to the buffer, what is the new pH of the solution?
pH of a buffer and buffer capacity Example: For a buffer solution consisting of 0.1 M acetic acid and 0.1M sodium acetate, The pH of the solution is 4.75. 4.75 4.75 10 0.1 0.1 10 [ ] [ ] [ ] [ ] [ ][ ] − − − + + − + − = • = = • = = + Ac HAc H Ka HAc H Ac Ka HAc H Ac If an amount of hydrochloric acid, equivalent to 10% of the acetate present, is added to the buffer, what is the new pH of the solution?
pH of a buffer and buffer capacity( Continued) After addition of HCl, the new [ac]=0.09M, [Hac]=0. 11M m1=ka。Hg LAC 0.11 =10 -4.75 10 4.66 0.09 pH=46 ypH=475-4.66=0.09 The addition of 0.01M strong acid to pure water would lower ph by 5 units(from 7 to 2)
pH of a buffer and buffer capacity (Continued) After addition of HCl, the new [Ac- ]=0.09M, [HAc]=0.11M 4.75 4.66 0.09 4.66 10 0.09 0.11 10 [ ] [ ] [ ] 4.7 5 4.6 6 = − = = = • = = • − − − + pH pH Ac HAc H Ka The addition of 0.01M strong acid to pure water would lower pH by 5 units (from 7 to 2)!
pH of a buffer and buffer capacity( Continued) The ph of a buffer depends on the pka of the buffer acid not its concentration HA=H+A Ka HTA I HA H]=。lHA [A J ph=PKa-loe(A
pH of a buffer and buffer capacity (Continued) • The pH of a buffer depends on the pKa of the buffer acid, not its concentration. [ ] [ ] log [ ] [ ] [ ] [ ] [ ][ ] − − + + − + − = − = • = = + A HA pH pKa A HA H Ka HA H A Ka HA H A
pH of a buffer and buffer capacity(Continued) Buffer capacity is how much acid or base the buffer can tolerate while maintaining the pH( within a 1.00 unit) Buffer capacity is determined by the concentration of the buffer acid and its conjugated base, as well as their concentration ratio 12-0.8-0.400.40.81.2 log CNaA CHA
pH of a buffer and buffer capacity (Continued) • Buffer capacity is how much acid or base the buffer can tolerate while maintaining the pH (within a 1.00 unit). • Buffer capacity is determined by the concentration of the buffer acid and its conjugated base, as well as their concentration ratio