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Elevkåren Teknis

Due to the powerful spreadsheet of  Psion you are able to view a titration curve right at your labdesk.

The goal of this laboration is to discuss pKa and buffersolutions.

At the equivalent volume v_e= 24,5 cm³ you are able to calculate the amount of acetic acid. From the titration curve at v_e/2 you can estimate pK_a (HAc) to 4.6 or 4.7 which is close to the literature value. From the slope of the curve you can see that the changes in pH are small close to the pK_a. This is what we call an acid-base buffer. At the beginning of the curve the pH is 2,8 and from that value it is possible to calculate the K_a(HAc).

                HAc + H₂O <=> H₃O⁺  +  Ac^-

f t b            0,10                    0              0

at equil    0,10-10-2.8            10-2.8     10-2.8           

K_a = 10^-5.6/(0.1-10^-2.8)  = 2,5523E-5 

pK_a = 4,59 which is close to the value obtained directly from the curve.

The difference from literature may be caused by the school pH-meter and electrode.