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Unformatted text preview: 6. Buffers (17.2) A buffer solution resists change in pH when a strong acid or strong base is added, so buffer is a mixture of a weak acid and base. Need both conjugate pairs (acid and base) in solution: -- make buffer by mixing conjugate pair directly in solution-- make buffer by doing titration with strong acid or base HCOO + HCl HCOOH + Cl HCOOH + NaOH HCOONa + H 2 O (1) Add HCl to HCOOH/HCOO- buffer, weak base reacts to neutralize acid: (2) Add NaOH to buffer, weak acid reacts to neutralize base: Therefore, strong acid and strong base are neutralized by buffer solution, until one of the buffer components is depleted. e.g. Calculate pH of buffer 0.250 M HCOOH and 0.100 M HCOONa 2.15-- when you know you have a buffer, you can make an ice table for the weak acid, including the concentration of the conjugate base under initial conditions. This will be a small K problem (because acid is weak) so youll be able to make approx. and solve for x (and pH) K a = H 3 O + [ ] HCOO ! [ ] initial HCOOH [ ] initial Making an approx. means: Concentration initial ~ concentration at equil....
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- Spring '09