Answer:
3.16mL of glacial acetic acid must be added
Step-by-step explanation:
The mixture of acetic acid with sodium acetate produce a buffer. The buffer follows the H-H equation:
pH = pKa + log [A⁻] / [HA]
Where pH is the pH of the buffer: 5.0
pKa is pKa of the buffer = 4.74
[A⁻] could be taken as moles of acetate ion = 0.500L * (0.20mol/L) = 0.100mol
And [HA] are moles of acetic acid.
Replacing:
5.0 = 4.74 + log [0.100mol] / [HA]
0.26 = log [0.100mol] / [HA]
1.8197 = [0.100mol] / [HA]
[HA] = 0.100mol / 1.8197
[HA] = 0.05495 moles of acetic acid
As the glacial acetic acid is 17.4M, the volume we must add to prepare the buffer is:
0.05495 mol * (1L / 17.4mol) = 3.16x10⁻³L =
3.16mL of glacial acetic acid must be added