Vinegar

Determination of the Ka of a Weak Acid Introduction: Acids and radicals atomic number 18 oft described as being weak or salubrious. While this classification seems somewhat arbitrary, other more quantifiable descriptors exist. For bitings, Ka pass judgments are commonly affaird. The ionization of an blistering puke be shown by the following equation: HA(aq)(H+(aq)+A-(aq)(Eq. 1) Since an chemical substance equilibrium exists, an equilibrium constant, Ka, can be written: Ka=[H+] [A-](Eq. 2) [HA] The Ka value is an character of acid strength. The larger the value of the Ka, the stronger the acid. This value is trait of the acid and can be used to help aim an chartless acid. A similar system exists for plants (Kb). Two methods may be used to govern the Ka value. Both methods require the use of a pH meter. In the first method, a take of acid is titrated with base. The pH values are plotted vs. the plenty of base added. The equi valence acid is determined from the graph. Next, the masses of base central to the equivalence point is found, and the pH at this volume is noted. The [H+] identical to this pH is equal to the Ka for the acid. At a point midway to the equivalence point, [H+] = [HA] = [A-] for a monoprotic acid. Canceling out [A-] and [HA] in comparison 2 gives Ka = [H+].

The second method for determining Ka values involves a one-half volume method. A solution of the acid is vigilant and divide in half as accurately as possible. unrivaled portion is titrated to its endpoint with phenolphthalein. The both portions are thence recombined , and the pH of the resulting solution is me! asured. Since half of the acid has been titrated, [H+] = [HA] = [A-]. Again, if [A-] and [HA] are canceled in Equation 2, Ka = [H+]. The pH value of the combined solutions can be born-again to [H+] to give a Ka value. Purpose: The purpose of this taste is to determine the Ka value for a weak acid by two methods: potentiometric titration and half volume...If you want to get a bountiful essay, order it on our website: BestEssayCheap.com

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