what will be the pH of a 100mL buffer solution containing 0.064 M of acetic acid and 0.036M f sodium acetate, after addition of 1 millimole of the hydrochloric acid? pka=4.75
millimola HAc (acetic acid) = mL x L = 100 mL x 0.064 M = 6.4 mmols.
millimols Ac^- (acetate ion) = mL x L = 100mL x 0.036 M = 3.6 mmols.
When HCl is added the acetate reacts to limit the pH.
...............Ac^- + H^+ --> HAc
I.............3.6........0.............6.4
add.....................1................................
C........... -1.........-1..............+1......................
E............2.6..........0.............7.4....................
Plug the E line into pH = pKa + log (Ac^-)/(HAc) and solve for pH.
Post your work if you get stuck.
ph=4.75 + log (2.6/7.4) = 4.30 that right?
Looks good to me.
To determine the pH of the buffer solution after the addition of hydrochloric acid, we need to apply the Henderson-Hasselbalch equation.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log ([A-]/[HA])
In this equation, pKa represents the negative logarithm of the acid dissociation constant of the weak acid (acetic acid), [A-] represents the concentration of the conjugate base (acetate ion), and [HA] represents the concentration of the weak acid (acetic acid).
Given:
- Initial volume of the buffer solution = 100 mL
- Initial concentration of acetic acid (HA) = 0.064 M
- Initial concentration of sodium acetate (A-) = 0.036 M
- pKa (acid dissociation constant of acetic acid) = 4.75
- Addition of 1 millimole of hydrochloric acid (HCl)
Step 1: Calculate the concentration of acetic acid (HA) and acetate ion (A-) after the addition of HCl.
- Conversion of 1 millimole to mol: 1 millimole = 0.001 mol
- The total volume of the solution after HCl addition = 100 mL + 0.001 L (convert 1 millimole to liters)
- Concentration of acetic acid (HA) after HCl addition = (0.064 M * 100 mL) / (100 mL + 0.001 L)
- Concentration of acetate ion (A-) after HCl addition = (0.036 M * 100 mL) / (100 mL + 0.001 L)
Step 2: Calculate the new pH using the Henderson-Hasselbalch equation.
- pH = 4.75 + log ([A-]/[HA])
Plug in the calculated concentrations into the Henderson-Hasselbalch equation and solve for pH.