100922Chem116lecture

100922Chem116lecture - Making a buffer by adding about...

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0.1 mole CH 3 COOH + Na CH 3 COO 0.1 mole Making a buffer by adding about equimolar amounts of a weak acid and its conjugate base (as a salt) 0.1 mole H 3 PO 4 + Na H 2 PO 4 0.1 mole 0.1 mole NH 3 + NH 4 Cl 0.1 mole
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1.0 7.5 x 10 -3 3.5 x 10 -4 1.8 x 10 -5 4.3 x 10 -7 9.5 x 10 -8 6.2 x 10 -8 5.7 x 10 -10 5.6 x 10 -11 2.2 x 10 -13 1.0 x 10 -14 K a 1.0 1.3 x 10 -12 2.9 x 10 -11 5.6 x 10 -10 2.3 x 10 -8 1.1 x 10 -7 1.6 x 10 -7 1.7 x 10 -5 1.8 x 10 -4 4.5 x 10 -2 1.0 x 10 -14 K b Strong bases in water Strong acids in water Moderately weak conjugates are useful for buffers
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Understanding titration curves for weak acids titrated with strong base is key to understanding buffers all CH 3 COOH all CH 3 COO - ½ equivalence point buffer region Know: • curve shape • eq. points • buffer region • pH calcs
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Polyprotic acids – can sequentially dissociate protons 1 st proton – dissociates most easily (highest K a ) 2 nd or 3 rd proton – dissociate less readily (lower K a s) Selecting a buffer when you want pH ~ 7
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100922Chem116lecture - Making a buffer by adding about...

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