# Determination of the Dissociation Constant of a Weak Acid.docx

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Determination of the Dissociation Constant of a Weak AcidLab Instructor-David PascitelliWednesday, 11:10am-2:00pmSection 121-08April 19, 20171
Purpose: This experiment use titration of an acid and a base to determine the dissociationconstant of a weak acid. The first part of the experiment is to determine the pkaof and unknownacid by titrating the base NaOH with the acid KHP. During the titration process the pH of theacid is measured and recoded. Once NaOH had neutralized with KHP calculation are made todetermine the pkaof the acid. Part two of the experiment discovers the concentration of theunknown acid. A byproduct of the first part of the experiment discovered the amount of NaOHneeded to neutralize KHP. Acquiring the molarity and volume of the base the concentration ofthe acid KHP can be calculated.Introduction: According the Bronsted- lowery acid base theory acids donate protons. A baseaccepts a proton. Strong acids have weak conjugate bases and weak acids have strong conjugatebases. Loosely defined Disassociation is when ionic molecule spits into smaller part. A strongacid will completely dissociate in a solution. A weak acid only partially disassociates.Thedissociation constant is represented as ka. the formula for the dissociation constant is representedas the products over the reactants ka= [products]/[reactants]. In a generic equation where HA(aq)+H2O(l)= H3O++A-(aq)the ka=( [H3O+][ A-(aq)]/[ HA(aq)]). The equation of pH is –log[H3O+]=pH. Bymanipulating the dissociation constand equation and the pH equation you end with a finalequation where pH= pka-log([ HA]/[A-]) the purpose of titration is to determine the half theamount of base needed in the reaction. By taking half the amount of base required the reaction

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