In: Chemistry
For each of the following solutions, calculate the initial pH and the final pH after adding 0.005 mol of NaOH. 210.0 mL of a buffer solution that is 0.315 M in CH3CH2NH2 and 0.285 M in CH3CH2NH3Cl Express your answers using two decimal places separated by a comma.
Moles of base = 0.315 * 0.210 = 0.06615
Moles of salt (conjugate acid) = 0.285 * 0.210 = 0.05985
Using equation:
pOH = pKb + log(moles of salt/moles of base)
For ethylamine, pKb = 3.3
Thus,
pOH = 3.3 + log(0.05985 / 0.06615) = 3.256
Thus, initial pH = 14 - pOH = 10.744
Moles of base NaOH added = 0.005
After addition of moles of NaOH,
Moles of base in the buffer solution = 0.06615 + 0.005 = 0.07115
Moles of salt in the buffer solution = 0.05985 - 0.005 = 0.05485
Putting values in the equation:
pOH = pKb + log(moles of salt/moles of base)
pOH = 3.3 + log(0.05485 / 0.07115) = 3.187
Thus,
pH = 14 - pOH = 10.813