The acetate buffer were prepared by mixing 0.1 M ch3cooh with 0.1M ch3cooNa in the ratio 8:2 and 2:8. Calculate the resulting ph after the addition of 2mL of 0.1 M HCl to 10 ml of buffer 8:2 and 4ml of 0.1 M NaOH to 10 ml of buffer 8:2.
To calculate the resulting pH of the buffer solution after the addition of acid or base, we need to consider the Henderson-Hasselbalch equation. The Henderson-Hasselbalch equation allows us to calculate the pH of a buffer solution based on the concentrations of the acid and its conjugate base.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log ([A-] / [HA])
Where:
- pH is the logarithmic measure of the acidity or basicity of a solution
- pKa is the negative logarithm of the acid dissociation constant, a measure of the strength of the acid
- [A-] is the concentration of the conjugate base of the acid
- [HA] is the concentration of the undissociated acid
In this case, we have a buffer solution prepared by mixing acetic acid (CH3COOH) and sodium acetate (CH3COONa). The acetic acid is the acid (HA) and the sodium acetate is the conjugate base (A-).
Let's consider the first scenario where 2 mL of 0.1 M HCl (a strong acid) is added to 10 mL of the buffer solution prepared in the ratio 8:2 (acid to conjugate base).
1. Calculate the initial concentrations of the acid and the conjugate base:
- Acetic acid (CH3COOH):
Initial volume = 10 mL (buffer) + 2 mL (HCl) = 12 mL
Initial concentration = (0.1 M) * (8/10) = 0.08 M
- Sodium acetate (CH3COONa):
Initial volume = 10 mL
Initial concentration = (0.1 M) * (2/10) = 0.02 M
2. Calculate the concentration of the acid and the conjugate base after the addition of the acid:
- Acetic acid (CH3COOH):
Final volume = 12 mL
Final concentration = (0.08 M) * (12/12) = 0.08 M
- Sodium acetate (CH3COONa):
Final volume = 10 mL (unchanged)
Final concentration = (0.02 M) * (10/10) = 0.02 M
3. Calculate the pH using the Henderson-Hasselbalch equation:
- pKa for acetic acid is approximately 4.76
- [A-] = 0.02 M (concentration of sodium acetate)
- [HA] = 0.08 M (concentration of acetic acid)
pH = 4.76 + log (0.02 M / 0.08 M)
pH = 4.76 - log 4
pH ≈ 4.76 - 0.602
pH ≈ 4.16
The resulting pH after the addition of 2 mL of 0.1 M HCl to 10 mL of the buffer solution 8:2 is approximately 4.16.
You can follow a similar process to calculate the resulting pH in the second scenario where 4 mL of 0.1 M NaOH (a strong base) is added to 10 mL of the buffer solution 8:2. Remember to adjust the concentrations of the acid and the conjugate base accordingly before calculating the pH using the Henderson-Hasselbalch equation.