BCHE 395-3 2013 pH Buffers Titrations

# And tests small change in organisms ph

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Unformatted text preview: H+ remaining Step 3: use the H- H equaYon to calculate pH pK (Tris- HCl) = 8.30 (so how do we get these? Given!) pH = pK + log(conj.base/conj.acid) = 8.30 + log (0.3 X 10- 3 moles/80ml) (0.2 X 10- 3 moles/80ml) 8.30 + log(0.3/0.2)= 8.30 + log(1.5)= 8.30 + 0.18 = pH 8.48 - TitraYon •  TitraGon: adding incremental amounts of a base to an acid •  Monitor changes in pH of soluYon Acts as reservoir •  Ex. MonoproYc biochemical acid (aceYc acid) and YtraYng with strong base (OH- ) or acid (H+) TitraYon Curves: Landmarks! AceYc acid •  pK values can be measured experimentally •  Dissolve weak acid in water, add strong base slowly, measure pH •  Plot amount of base on X axis, pH change on Y axis •  At midpoint of curve, pH = pKa •  Conjugate [acid] = Conjugate [base] •  H- H; log 1 = 0 TitraYon Curves: Landmarks! •  If you understand the landmarks, this concept becomes very simple •  Be able to READ YtraYon curves! [CH3COOH] > [CH3COO- [CH3COOH] < [CH3COO- Biological Buﬀers •  •  •  •  •  •  •  •  pKs ~4.5 ~8.7 ~1.96 ~6.70 ~ 12.44 ~6.38 ~10.33 weak acid R- COOH ß།à༎ R- NH3+ ß།à༎ H3PO4 ß།à༎ H2PO4- ß།à༎ HPO42- ß།à༎ H2CO3 ß།à༎ HCO3- ß།à༎ weak base R- COO- + H+ R- NH2 + H+ H2PO4- + H+ HPO42- + H+ PO43- + H+ HCO3- + H+ CO32- + H+ Weak acids have diﬀerent pKas PolyproYc Acids •  Some acids tha...
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