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Unformatted text preview: Calculating the pKa of an Acid Using the Half-Neutralization Method Introduction Acid-base reactions involve neutralization between an acid and a base. The ability of an acid to donate its proton is dependent on the strength of the acid. Strong acids will completely dissociate the concentration of [H + ] in a 0.1 M solution of HCl is 0.1 M. However, weak acids only partially dissociate and will only form a smaller concentration of H + relative to the HA present. As with any equilibrium constant for any reaction, the constant is a ratio of the concentration of the products to the concentration of the reactants. For the weak acid reaction HA ( aq ) H + ( aq ) + A- ( aq ) the equilibrium constant K a is K a = [H + ][A- ]/[HA] The value of K a lets us determine whether the equilibrium lies to the left or to the right, and thus the strength of the acid. If you take a weak acid and titrate it with a strong base such as NaOH, partway through the titration, you will reach what is known as the half-equivalence point . This is the point where the concentration of acid and deprotonated acid are equal to each other also equal to half an equivalent of base having been added (by definition, at the endpoint of...
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