Question

A buffer that contains 0.470 M base, B, and 0.343 M of its conjugate acid, BH, has a pH of 9.13. What is the pH after 0.0020 mol of HCl is added to 0.250 L of this solution? pH =

Answer 1

0.470 ] = 0.118 mol = 0.086 mol POH=14-pH=14- 9.13 = 4.87 According to Henderson-Hasselbalch equation pOH = pkb + log(salt/Weak Base] 4.87 =pKb + log / 0.343 pKb= 5.007 volume of HCI = 0.250 L number of moles = Molarity > Volume initial no. of moles of B = 0.470 x 0.250 initial no. of moles of BH+ = 0.343 x 0.250 initial no. of moles of HCl = 0.0020 mol Construct ICA table to obtain their equilibrium concentrations: Reaction B + HC → BH+ concentration(mol) 0.118 0.0 0.086 change(mol) -0.002 -0.002 0.002 equilibrium(mol) 0.116 0.000 0.088 According to Henderson-Hasselbalch equation pOH = pkb + log(salt/Weak Base] POH= 5.007 + log [ 0.088 POH= 4.89 pH = 14 - POH= 14 - 4.89 = 9.11 pH= 9.11 | 0.116 ]