How to calculate pKa/pKb and Ka/Kb using the 1/2 equivalent point

[LinzMeaux]

Using the half equivalent point, determine the pKa and the Ka for the acids.  Compare the calculated values to the theoretical values recorded in your textbook.  Calculate % error.

HCl titrated with NaOH 1/2 equiv about 13.5 mL, pH = 1.35
HC2H3O2 titrated with NaOH 1/2 equiv about 13 mL, pH = 4.56


Also have to do it for the bases: pKb and Kb

NH3 titrated with HCl 1/2 equiv about 11 mL, pH = 9.24
NH3 titrated with HC2H3O2 1/2 equiv about 12 mL, pH =  9.4

[maddy]

Write out the value for Ka; Ka = [products]/[reactants]

You'll need to find the concentrations for your acids and bases.

[Chemistry Tutor]

halfway between the start of the titration and the equivalene point is the 1/2 equivalence point.

at this point the pH will be equal to the pka

the Ka = 10^-pka

[LinzMeaux]

THANK YOU!  That actually makes perfect sense.  For some reason I expected it to be harder than it was.  Silly me!