a 250.0ml buffer solution is 0.250M in ascetic acid and 0.250M in sodium acetate.
B). What is pH after addition of 0.0050mol of HCl?
C). What is pH after addition of 0.0050mol of NaOH?
250 mL x 0.250M = 62.5 millimols HAc
250 mL x 0.250M = 62.5 mmols NaAc.
add 5 mmols HAc
add 5 mmols NaOH
............Ac^- + H^+ ==> HAc
initial.....62.5..........62.5
add................5...........
change......-5....-5......+5
equil.....57.5.....0......67.5
Substitute into the Henderson-Hasselbalch equation and solve for pH.
The same process will work the NaOH part.
equil.....
To find the pH after the addition of HCl or NaOH to the buffer solution, we need to consider the reaction that occurs between the added acid/base and the components of the buffer.
In this case, the buffer consists of acetic acid (a weak acid) and sodium acetate (a salt of the weak acid).
B) To find the pH after adding 0.0050 mol of HCl, we need to consider the reaction of HCl with the acetate ion (Ac-) from sodium acetate. The reaction between a strong acid (HCl) and a weak base (Ac-) will lead to the formation of the weak acid (acetic acid) and water.
The balanced equation for the reaction can be written as follows:
HCl + Ac- -> HAc + Cl-
Since the amount of HCl added is given in moles, we need to calculate the new concentrations of acetic acid and acetate ion in the buffer solution.
The initial concentration of acetic acid is 0.250 M, and we are adding 0.0050 mol of HCl. The volume of the buffer solution is 250.0 ml, so the final volume will be 250.0 ml.
1. Calculate the new concentration of acetic acid:
Initial moles of acetic acid = initial concentration * initial volume
New moles of acetic acid = initial moles of acetic acid - moles of HCl added
New concentration of acetic acid = new moles of acetic acid / final volume
2. Calculate the new concentration of acetate ion:
Since the buffer contains equal initial concentrations of acetic acid and sodium acetate, the initial concentration of acetate ion is also 0.250 M.
New moles of acetate ion = initial moles of acetate ion + moles of HCl added
New concentration of acetate ion = new moles of acetate ion / final volume
Once you have the new concentrations of acetic acid and acetate ion, you can use the Henderson-Hasselbalch equation to calculate the pH of the buffer solution. The Henderson-Hasselbalch equation is given by:
pH = pKa + log([Ac-] / [HAc])
The pKa of acetic acid can be found in reference materials and is approximately 4.75.
C) To find the pH after adding 0.0050 mol of NaOH, we need to consider the reaction of NaOH with the acetic acid present in the buffer solution. The reaction between a strong base (NaOH) and a weak acid (acetic acid) will lead to the formation of sodium acetate and water.
The balanced equation for the reaction can be written as follows:
NaOH + HAc -> NaAc + H2O
Similar to part B, we need to calculate the new concentrations of acetic acid and acetate ion in the buffer solution after the addition of NaOH.
The initial concentration of acetic acid is 0.250 M, and we are adding 0.0050 mol of NaOH. The final volume remains the same at 250.0 ml.
1. Calculate the new concentration of acetic acid:
New moles of acetic acid = initial moles of acetic acid - moles of NaOH added
New concentration of acetic acid = new moles of acetic acid / final volume
2. Calculate the new concentration of acetate ion:
Since the buffer contains equal initial concentrations of acetic acid and sodium acetate, the initial concentration of acetate ion is also 0.250 M.
New moles of acetate ion = initial moles of acetate ion
New concentration of acetate ion = new moles of acetate ion / final volume
Once you have the new concentrations of acetic acid and acetate ion, you can again use the Henderson-Hasselbalch equation to calculate the pH of the buffer solution using the pKa value of acetic acid.