CH 204 Report Experiment 8 - CH 204 Introduction to...

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CH 204 – Introduction to Chemical PracticeExperiment # 8 – Weak Acids and Buffers INTRODUCTIONThis lab focuses on a weak acid and a buffered solution. Acids are compounds that dissociateto produce H3O+ ions while bases are compounds that dissociate to produce OH- ions. The strength of an acid or a base depends on how much each of them dissociate or the degree of dissociation. For strong acids and bases, they dissociate completely in a solution while weak acids and bases only slightly dissociate. In this lab, the observations of weak acids and buffers will be recorded and analyzed. A buffer solution’s pH is not dramatically affected upon the addition of a strong acid or a strong base until its buffering capacity has been reached. The buffering capacity is the number of moles of strong acid or strong base added to the solution to change 1 liter of buffer solution by a pH unit of 1. In fact, buffers are present in everyday life out of a chemistry setting as well. Buffers help maintain homeostasis and help regulate pH and the environments in living organisms. For example, blood is a natural buffer as it usually maintains a pH of 7.4 and resists changes from the addition of acids or bases to it. The important buffer in blood is the bicarbonate ion and dissolved carbon dioxide in the form of carbonic acid that help prevent pH fluctuations in the blood upon additions ofvarious acidic or basic solutions.2Furthermore, the Henderson-Hasselbalch equation, pH=pka + log([A-]/[HA]), describes the relationship between the pH of a given buffer, the concentrations of each buffer component, and the Ka or the acid dissociation constant of the acidic solution being observed. It was derived from the acid dissociation constant equation, Ka=[H+][A-]/[HA], by Lawrence Joseph Henderson who was trying to describe the use of carbonic acid as a buffer solution. Later, Karl Albert Hasselbalch expressed the formula in logarithmic terms when studying metabolic acidosis, leading to the Henderson-Hasselbalch equation.3By utilizing this equation, the theoretical pH of a buffer can be determined. At the equivalence point, all of the acid should be neutralized by the base and at the half-equivalence point, the pKa should equal the pH at the half-equivalence point since the molar ratio of the concentration should equal 1:1, therefore making log[1]=0. Furthermore, pH of a solution can be determined by taking the negative log of the concentration of H+ ions present in the solution. If pH is less than 7, then the solution is acidic. If thepH is greater than 7, then the solution is basic. If it equals 7, then the solution is neutral. To calculatethe pH of a solution, the negative log of the H3O+ concentration of the solution must be taken. The other method to determine acidity or basicity is to examine the pOH which is essentially the opposite of pH and looks at OH- concentration in a solution instead.

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