This is for an unknown weak acid Find the molarity molL and

*This is for an unknown weak acid*

Find the molarity (mol/L) and the estimated pKa of the unknown weak acid.

10mL of the unknown weak acid was mixed with 40mL of deionized water.

I used .075M NaOH, which was the titrant.

Here is the graph:

Here are the possible unknown weak acids to choose from and their Ka\'s:

Solution

The pKa = pH at the midpoint, in order to find the midpoint exactly you should find the second derivative of your curve, at the inflection point between 0 and 10 mL that will be your pKa. But if you don\'t know the calculus behind it just divide your endpoint by 2 to estimate it, 12.7/2 = 6.35, at 6.35 or very close to it try to estimate the pH. That number then goes into the calculation pH= pKa = -log(Ka), in order to solve for Ka use 10^-pH , that will give you Ka and you can then identify the acid.