Question

how could you use 1.0M lactic acid and 1.0M NaOH (instead of lactate) to make 200ml of a 0.25M lactate buffer, ph 4.0?

Answer 1

M\(_1\)V\(_1\) = M\(_2\)V\(_2\)

Answer 2

You need to take the required pH into account.
M1V1 = M2V2 would mean neutralisation.

Answer 3

always remember if its an weak acid to a strong base its 1 : 1/2 equivalence

That will make pH = pka or Conjugated base [A-] = HA