Can you calculate the acid dissociation constant (Ka) of a weak acid from experimental data?

Question

Ellie Andrews · Accepted Answer

Yes, we can, but first we need some experimental data.......and someone must first do the measurement....

We question the equilibrium. #HA(aq)+H_2O(aq) rightleftharpoonsA^(-) + H_3O^+# Now #K_a=([H_3O^+][A^-])/([HA])# Now it is a fact, that #[H_3O^+]# for a #1.0*mol*L^-1# solution of #"acetic acid"# is #4.24xx10^-3*mol*L^-1#. And I got these data from the interwebz; of course someone had to measure these data..... #H_3C-CO_2H(aq)+H_2O(aq) rightleftharpoonsH_3C-CO_2^(-) + H_3O^+# And #K_a=([H_3O^+][H_3C-CO_2^-])/([H_3C-CO_2H])# #=(4.24xx10^-3*mol*L^-1xx4.24xx10^-3*mol*L^-1)/(1.0*mol*L^-1-4.24xx10^-3*mol*L^-1)# #=1.81xx10^-5# #pK_a=-log_10(1.81xx10^-5)=??# Is that right?

Owen Ambrose · Answer

undefined Yes, the acid dissociation constant (Ka) of a weak acid can be calculated from experimental data. Ka is determined by measuring the concentration of the acid, the concentration of the dissociated hydrogen ions (H+), and the concentration of the conjugate base in solution at equilibrium. The expression for Ka is given by the ratio of the concentrations of the products (H+ and the conjugate base) to the concentration of the undissociated acid. Mathematically, it is represented as:

Ka = [H+][A-] / [HA]

Where:
- [H+] is the concentration of hydrogen ions in solution.
- [A-] is the concentration of the conjugate base.
- [HA] is the concentration of the undissociated acid.

Experimental techniques such as titration or spectroscopy can be used to measure these concentrations and determine Ka. Once the experimental values are obtained, Ka can be calculated using the formula mentioned above.