CH 204 – Introduction to Chemical Practice Experiment #8 – Weak Acids and Buffers INTRODUCTION In this experiment a solution of acetic acid was titrated with sodium hydroxide in order find the equivalence point and half equivalence points of the titration. Acetic acid was then buffered and prepped for further titration with NaOH and HCl in order to understand the effects of buffering with the addition of a strong acid/base so that buffering capacities could be determined. Specifically the analytical technique of titration was used in this experiment to quantitatively find the equivalence point and half equivalence point of a species in a solution by reacting it with a second species of a known concentration. In titrations of weak acids and strong bases pH is closely monitored so that the equivalence point and endpoints are clear and then using the volume of titrant signified by these points the original concentration, equivalence point, and half equivalence points can be calculated to ultimately determine the buffering capacity of the solution. The technique of titration originated from the late 18thcentury in France with a man Named Francois Antoine Henri. He created a rudimentary burette that was improved upon by Joesph Louis Gay- Lussac. He actually coined the terms pipette and burette in 1824.1The most recent major renovation to the burette and titration technique was made by Karl Friedrich Mohr. He redesigned it by placing a clamp on the burette and a tip at the end in 1855.2 The theory behind titrations of weak acids and strong bases is based in the idea that the strength of and acid or a base depends on the degree of dissociation. A weak acid or base dissociates only slightly. For a weak acid the extent of H3 O+ formation can be described by the acid-dissociation constant Ka , which is a ratio of the products over the reactants of an acid-dissociation equation. The larger the Kathe stronger the acid. The characteristic property of water that the Kw of water is 1.0 x 10-14forms the basis of an aspect of acid-base theory that is widely recognized, the pH scale. When the pH of a solution is greater than 7 the solution is basic, when the pH is less than 7 it is acidic, when the pH is equal to 7 it is neutral. Kw can be related to the concentration of hydronium and hydroxide by the equation+¿ H3 O ¿ ¿ −¿ O H ¿ Kw =¿ and pH can be solved for using the equation+¿ H3 O ¿ ¿ pH=−log¿ . The pH scale can also be converted to pOH if need be. This means that solutions with a low pOH are basic and solutions with a high pOH are acidic. The pOH can be solved for using the equation−¿ O H ¿ ¿¿ pOH=−log¿ Furthermore, when a weak acid and strong base are mixed a buffer is formed. A buffer is a solution that resists dramatic changes in pH upon the addition of strong acids 1 Szabadváry, F. "Joseph Louis Gay-Lussac (1778–1850) and Analytical Chemistry." <i>Talanta</i> 25.11-12(1978): 611-17. Web. 1 Nov. 2015.
