A buffer solution is prepared by mixing 14.9 mL of 0.0420 M phenylammonium chlor
ID: 692493 • Letter: A
Question
A buffer solution is prepared by mixing 14.9 mL of 0.0420 M phenylammonium chloride with 50.1 mL of 0.0306 M phenylamine (aniline). A table of pka values can be found here 1. Calculate the pH (to two decimal places) of this solution. Assume the 5% approximation is valid and that the volumes are additive. Tries 0/99 2. Calculate the pH (to two decimal places) of the buffer solution after the addition of 0.0974 g of phenylamine (aniline) (C6HsNH2) to the buffer solution above Assume 5% approximation is valid and that the volume of solution does not change.Explanation / Answer
pH = pka + log(base/acid)
base = phenylamine
acid = phenylammonium chloride
pka of phenylamine = 4.63
no of mol of phenylamine = 50.1*0.0306 = 1.533 mmol
no of mol of phenylammonium chloride = 14.9*0.042 = 0.626 mmol
so that,
pH = 4.63 + log(1.533/0.626)
pH = 5.02
2. no of mol of phenylamine added = 0.0974/93.13*10^3 = 1.046 mmol
pH = 4.63 + log((1.046+1.533)/0.626)
= 5.24
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