Question

If the dissociation constant of a weak acid is 6.4 x 10, at what ratio should you adjust the concentration of the weak acid and its conjugate base in ord a) 0.0500 M weak acid with 0.100 M conjugate base b) 0.100 M weak acid with 0.0100 M conjugate base c)0.500 M weak acid with 0.500 M conjugate base d) 0.0500 M weak acid with 0.500 M conjugate base e) 0 200 M weak acid with 0.100 M conjugate base

Answer 1

for a buffer

pH = -log Ka + log( [cojugate base / acid])

given

pH = 4.19

Ka = 6.4 x 10-5

plug in the values

4.19 = -log (6.4 x 10-5) + log([conjugate base/acid]

log(conjugate base/acid) = 4.19 + log (6.4 x 10-5)

log([conjugate base /acid]) = -0.00382

[conjugate base/acid] = 10^(-0.00382)

[conjugate base/acid] = 0.99

so the ratio of conjugate base and acid must be equal to 1

from the given options , c satisfy this

so

C) 0.5 M weak acid with 0.5 M conjugate base