Whenever a WEAK BASE reacts with a STRONG ACID we use an ICF Chart to determine the pH of the solution.
Concept #1: Understanding Weak Acid–Strong Base titration reactions
Concept #2: If you use an ICF Chart and at the end you have remaining weak acid and conjugate base then you have a buffer so you use the Henderson-Hasselbalch Equation to find pH.
Concept #3: If any excess moles of the strong acid remain then we will use its concentration to find the pH of the solution.
Concept #4: If the moles of both the conjugate base and strong acid are equal then we will have only weak acid at the end of our ICF Chart Calculation. To find pH we would follow up with an ICE Chart.
A buffer contains 167.2 mL of 0.25 M propanoic acid, CH3CH2COOH, with 138.7 mL of 0.42 M sodium propanoate, CH3CH2COONa. Find the pH after the addition of 150.2 mL of 0.56 M HCl. The Ka of CH3CH2COOH is 1.3 x 10-5.
Example #2: Calculate the pH of the solution that results from the mixing of 75.0 mL of 0.100 M NaC2H3O2 and 75.0 mL of 0.150 M HC2H3O2 with 0.0025 moles of HBr. Ka of HC2H3O2 is 1.8 x 10-5.