(5 pts) What is the pH of a 1-L buffer solution generated from 0.4 M hydrogen ph
ID: 1039605 • Letter: #
Question
(5 pts) What is the pH of a 1-L buffer solution generated from 0.4 M hydrogen phosphat -HPO42-(weak acid and 0.9 M phosphate (conjugate base)? Ka-3.6x 10-5 6. 7. (5 pts) Which of the following weak acid/conjugate base pairs is best suited for buffer a solution to a pH of 11.5? Explain your decision to get a full credit. Weak Acid Acetic Acid (CH COOH) Dihydrogen phosphate (H2PO) Hydrogen phosphate (HPO4) 6.2 x 108 Hydrogen phosphate (HPO,) Phosphate (POA) Conjugate Base Acetate (CH3COO) Ka 1.8 x 105 3.6 x 10-13Explanation / Answer
6)
Ka = 3.6 x 10^-13
pKa = 12.44
pH = pKa + log [salt / acid]
= 12.44 + log [PO43- / HPO42-]
= 12.44 + log [0.9 / 0.4]
pH = 12.79
7)
the suitable pair :
weak acid / conjugate base pair = HPO42- / PO43-
here the pKa = 12.44
this is very nearer to the given pH = 11.5 .
pH range of buffer = pKa + / - 1
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