In: Chemistry
A buffer solution based upon sulfurous acid was created by treating 1L of 1M sulfurous acid with NaOH until a pH of 1.347 was achieved (assuming no volume change). To this buffer 1.170 moles of NaOH were added (assume no volume change). What is the final pH of this solution? Assume 5% assumption is valid.
moles of H2SO3 = 1 x 1 = 1
H2SO3 + NaOH --------------------> NaHSO3 + H2O
1 x 0
1-x 0 x
pH = pKa1 + log [NaHSO3 ]/[H2SO3 ]
1.347 = 1.85 + log ( x / 1-x)
x / 1- x = 0.314
x = 0.314 - 0.314 x
x = moles of NaHSO3 = moles of NaOH
moles of NaOH = 0.240
moles of H2SO3 = 1
on addition of 0.170 moles NaOH :
pH = 1.85 + log [0.240 + 0.170 / 1.0 -0.170]
pH = 1.54
final pH = 1.54
note : NaOH moles i think 0.170 moles not 1.170. if 1.170 moles NaOH is taken buffer will fail. verify once