PH and Buffers.

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Presentation transcript:

pH and Buffers

HA NaOH 0.1-0.02 0.02 A- H+ OH- Na+ 0.02 0.02 0.02 0.02 H2O

A- HCl 0.1-X X H+ Cl- X X HA X

0 0.05 0.1 M NaOH ® pH pKa 4.76 2.88

How would you choose a good buffer for an enzyme that is active at a particular pH? Compare the pKas. Acid/base pKa Carbonic acid pK1 3.77 Bicarbonate pK2 10.24 Acetate 4.76 Imidazole 6.99 Tris 8.2 Ammonium 9.25 Phosphate pK1 2.15 Phosphate pK2 7.20 Phosphate pK3 12.40

Summary The Henderson-Hasselbach equation relates pH to concentrations of conjugates of weak acids and bases. Titrations of weak acids and bases identify the pKa (and pKb). Any weak acid or base provides a pH buffer around its pKa.