Question

Using the following pH curve for the titration of a weak acid with a strong base, if the pH at half-equivalence point is 4.75, what is the Ka of the weak acid? Equivalence Point Half-equivalence Point - 8 12 14 Volume of base added (in ml) 20 1.78 x 10-4 1.77 x 10-4 1.77 x 10-5 1.78 x 10-5

Answer 1

pH=-logK_a

=> 4.75=-logK_a

_=> logK_a=(-4.75)

=> K_a=antilog(-4.75)=1.78x10^-5

Using the formula of pH, the acid dissociation constant, K_a is found to be 1.78x10^-5