Lecture 20 - Lecture 20: Examples of Acid-base Equilibria...

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Lecture 20: Examples of Acid-base Equilibria We assume that the concentration of water is a constant (55 M), so we don’t include it in the equations using K a . Very strong acids like H 2 SO 4 , HCl, HBr, HI, HNO 3 , HClO 4 : we assume that the concentration of the pure acid in water = [H 3 O+]. The pKa is essentially zero in water, though the scale is extended in other solvents. We assume that all of the H 3 O+ is available to protonate all bases present, starting with the strongest bases. Reminder: a base is anything that has electrons that can form a bond to a proton. A strong base is a substance whose conjugate acid is weak! Moderately strong acids like HF, H 3 PO 4 , CH 3 COOH have pK a in the range of 3-6. That means that [H 3 O+] is in the range of 10 -2 to 10 -6 if the pure acid is added to water. The pH is of course 2-6. Buffer pH, when the acid and its conjugate base are both added, is 3-6. If substantial amounts of the pure acid, like 1 M concentration, is added, we can assume that the concentration of the original acid does not change much. The
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This note was uploaded on 09/29/2009 for the course ME 530.230 taught by Professor Katz during the Spring '09 term at Johns Hopkins.

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