[magn6357]

Problem: By mixing 100 mL of 0.037 M 3-chlorobutyric acid with 0.1 M NaOH you get a buffer solution between 3-chlorobutyric acid and its corresponding base. You then have to figure out the volume of NaOH you have to use such that the pH value is 4.3. The acid dissociation constant of 3-chlorobutyric acid is 8.9*10^-5 M.

Solution:
First I use the Henderson-Hasselbach equation:
pH=pK_a + log([A ^-]/[HA])

Since the reaction is in the ratio 1:1 and NaOH is a strong base all NaOH must get converted to the corresponding base.
The amount of substance of acid after the reaction must equal the original amount of substance minus the amount of substance of NaOH.
Thus you get the equation:
pH=pK_a + log(n_NaOH/(n_acid-n_NaOH))

And then you can solve for the amount of substance of NaOH.
Then you can calculate the volume from the concentration of NaOH.

I would like to know if my solution is correct.
English is not my first language so sorry if this is hard to understand.

[chenbeier]

Yes should be correct.