Homework Soursecalculate a new concentration of buffer with the pH of 491 f
calculate a new concentration of buffer with the pH of 4.91 for 3.907mL of 1.0 M acetic Acid and 6.093mL of 1.0 M Sodium acetate and 90mL water with an addition of 2.90mL of 1.00 M NaOH is added. calculate a new concentration of acid and base. assuming you don\'t know the initial concentration of acid and base.
there are 3 ways to solve this.
1. assume that both of the acid and base concentration are correct
2. assume that only one of the concentration is correct.
3. assume that none of the concetration are corrected. (and this is what I want to solve, by the third method)
there are 3 ways to solve this.
1. assume that both of the acid and base concentration are correct
2. assume that only one of the concentration is correct.
3. assume that none of the concetration are corrected. (and this is what I want to solve, by the third method)
Solution
The equation you will use is the Henderson-Haselbalch equation: pH = pKa + log [HCOO-]/[HCOOH] Since both of your solutions are at the same concentration, when you combine equal volumes of those two solutions, you have just doubled the volume, and halved the concentration of each compound. So, [HCOOH] = [HCOO-] = 0.125 M Plugging those in the H-H equation, pH = 3.77 + log [HCOO-]/[HCOOH] pH = 3.77 + log 1 = 3.77 Any time the concentration of the acid and conjugate base in a buffer solution are the same, the pH will equal the pKa of the weak acid. For your second question, calculate the moles of HCl added to the buffer solution and the actual moles of both the HCOOH and HCOO- in the buffer solution using moles = molarity X volume. When you add HCl to a buffer solution, the moles of the base (HCOO-) will be DECREASED by the moles of HCl added, and the moles of HCOOH will be INCREASED by that same amount. Just plug those new numbers of moles into the H-H equation and calculate the pH.
