<u>Answer:</u> The maximum volume of HCl that can be added before its buffering capacity is lost is 111.3 mL
<u>Explanation:</u>
We are given:
Concentration of buffer = 0.460 M
To calculate the pH of acidic buffer, we use the equation given by Henderson Hasselbalch:
.....(1)
We are given:
= negative logarithm of acid dissociation constant of benzoic acid = 4.2
pH = ?
Putting values in equation 1, we get:
When the pH of the buffer changes by 1 unit, the buffering capacity is said to be lost.
pH change for loosing buffer capacity = [4.2 - 1] = 3.2
Calculating the ratio of conjugate base and its acid by using equation 1:
= 4.2
pH = 3.2
Putting values in equation 1, we get:
- To calculate the number of moles for given molarity, we use the equation:
......(2)
For benzoic acid and its conjugate base:
Molarity of benzoic acid and its conjugate base = 0.460 M
Volume of solution = 115 mL
Putting values in equation 2, we get:
The chemical reaction for aniline and HCl follows the equation:
Let the moles of acid added to carry out the change is 'x' moles
- Calculating the moles of acid added:
Calculating the volume of acid added by using equation 2, we get:
Moles of acid added = 0.0434 moles
Molarity of solution = 0.390 M
Putting values in equation 2, we get:
Hence, the maximum volume of HCl that can be added before its buffering capacity is lost is 111.3 mL