What is the pH after 0.150 mol of HCl is added to the buffer from Part A? Assume
ID: 954174 • Letter: W
Question
What is the pH after 0.150 mol of HCl is added to the buffer from Part A? Assume no volume change on the addition of the acid. Express the pH numerically to three decimal places. Part A: pH = 6.248 What is the pH of a buffer prepared by adding 0.607 mol of the weak acid HA to 0.609 mol of NaA in 2.00 L of solution? The dissociation constant K a of HA is 5.66×10 7 .
Part C. What is the pH after 0.195 mol of NaOH is added to the buffer from Part A? Assume no volume change on the addition of the base.
Express the pH numerically to three decimal places.
Explanation / Answer
HCl gives H+ which adds to A- to become HA
HA moles = 0.607 + 0.15 = 0.757 , A- moles = 0.609-0.15 = 0.459
pH = pka + log [NaA}/[HA] where pka = -log Ka = -log ( 5.66x10^-7) = 6.247
pH = 6.247 + log ( 0.459/0.757) = 6.03
C) NaOH gives OH- , which reacts with HA to give A- ,
HA moles = 0.607-0.195 = 0.412 , A- moles = 0.609+0.195 = 0.804
pH = 4.247 + log ( 0.807/0.412)
= 4.537
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