Question

Glacial acetic acid is 99.5% acetic acid (f.w. 60.052) by weight and has a density of 1.05g/mL. Calculate the volume of glacial acetic acid needed to make 1L of the 0.100M pH 5.000 buffer.

Answer 1

pH = pKa + log [base] /[acid]

ka acetic acid = 1.8 x 10^ -5

5.000 = 4.752 + log [base] /[acid]

log [base] /[acid] = 0.248

[base] /[acid] = 1.77

now, molar amount of acid required to get pH = 5

1.77x + x = 0.100M

x = 0.0722 mol (this is acetic acid needed in the solution)

now weight = 0.0722 x 60.052 = 4.3237 g

volume needed = mass/density = 4.3237/1.05 = 4.1178 mL

as glacial acetic acid is 99.5%, so 99.5% of x needed to get 4.1178mL

so volume needed = 4.1385mL