Titration question 2 equivalence points. Am i right?

[A_Munk3y]

Titration question 2! equivalence points. Am i right?

Homework Statement

this is the originial question.
A 0.149 g sample of a weak acid (HA) requires 16.80 mL of 0.110 M NaOH to completely reach the equivalence point. What is the Molar Mass of the acid?
and i got 86.63 g/mol. I have already made sure that it is right.

the question continues,
If the pH of the weak acid in question 1 (above) is 4,34 after 8.40 ml of the NaOH was added, what is the Ka of the acid?

Homework Equations

i think i remember this. At the half equivalence point, PH=PKa

The Attempt at a Solution

since PH=Pka at half equivalence point, the PH=10^-4.38
giving me 4.17x10^-5

am i right? :)

 

[symbolipoint]

Your concept is correct. I did not examine your values, so just trust your concept and you may do your own rechecking of the values.