Answer:
The pH change in 0,206 units
Explanation:
When the acetic acid buffer is at pH 5,000; it is possible to obtain the acetate/acetic acid proportions using Henderson-Hasselbalch formula, thus:
pH = pka + log₁₀ [A⁻]/[HA] Where A⁻ is CH₃COO⁻ and HA is CH₃COOH.
Replacing:
5,000 = 4,740 + log₁₀ [A⁻]/[HA]
1,820 = [A⁻]/[HA] (1)
As buffer concentration is 0,100M:
[A⁻] + [HA] = 0,100 (2)
Replacing (2) in (1)
[HA] = 0,035M
And [A⁻] = 0,065M
As volume is 1,80x10²mL, moles of HA and A⁻ are:
0,180L × 0,035M = 6,3x10⁻³mol of HA
0,180L × 0,065M = 1,17x10⁻²mol of A⁻
The reaction of HCl with A⁻ is:
HCl + A⁻ → HA + Cl⁻
The add moles of HCl are:
0,0065L×0,330M = 2,145x10⁻³ moles of HCl that are equivalent to moles of A⁻ consumed and moles of HA produced.
Thus, moles of HA after addition of HCl are:
6,3x10⁻³mol + 2,145x10⁻³ mol = 8,445x10⁻³ moles of HA
And moles of A⁻ are:
1,17x10⁻²mol - 2,145x10⁻³ mol = 9,555x10⁻³ moles of A⁻
Replacing these values in Henderson-Hasselbalch formula:
pH = 4,740 + log₁₀ [9,555x10⁻³ ]/[8,445x10⁻³ ]
pH = 4,794
The pH change in 5,000-4,794 = 0,206 units
I hope it helps!
