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Chemistry: An Atoms First Approach
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Chapter 13 / Exercise 12
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Computer 24 Advanced Chemistry with Vernier 24 - 1Determining Kaby the Half-Titration of a Weak Acid A common analysis of a weak acid or a weak base is to conduct a titration with a base or acid of known molar concentration to help determine the equilibrium constant, Ka, for the weak acid or weak base. If this titration is conducted very carefully and very precisely, the results can lead to a valid approximation of an equilibrium constant. In this experiment, however, you will use a different technique to determine the Kafor a weak acid, acetic acid. Your primary goal in this experiment is to calculate the Kaof acetic acid. The data that you will use to complete your calculations will come from the reaction of acetic acid with a solution of NaOH. Recall from your work with weak acid-strong base titrations that the point at which a reaction is half-titrated can be used to determine the pKaof the weak acid. In this experiment, the half-titration point will exist when you have added half as many moles of HC2H3O2as moles of NaOH. Thus, OHwill have reacted with half of the HC2H3O2, leaving the solution with equal moles of HC2H3O2and C2H3O2. At this point, according to the Henderson-Hasselbalch equation, ]OHHC[]OHC[log232232apKpHif there are equal moles of HC2H3O2and C2H3O2at the half-titration point, then pKais equal to the pH value of the solution. In this experiment, you may find it surprising that you do not need to keep close track of the volume of NaOH titrant added, as you would in most titrations. It is also unusual to conduct a
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Chemistry: An Atoms First Approach
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Chapter 13 / Exercise 12
Chemistry: An Atoms First Approach
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