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Lab Report:Acid/Base Stoichiometry EquilibriumPurpose:This lab has two purposes. The first purpose is to standardize a sodium hydroxide using apotassium hydrogen phthalate (KHP) solution. Secondly, this lab aims to determine a weak acid'sidentity by titrating it with the already standardized sodium hydroxide solution, creating atitration curve to determine the pKaof the weak acid.Introduction:Acid/ base titration was used to find an unknown substance's concentration from a knownsolution or standard solution. The titration technique has two solutions: the analyte or theunknown and the titrant, the known or precise concentration. A standardized solution is graduallyadded to the unknown concentration solution until the chemical reaction is complete.Standardization of NaOH is needed in the first experiment because NaOH absorbs water fromthe air, and it cannot be accurately weighted to calculate its concentration. KHP is used as aprimary standard to calculate NaOH's molarity in the first part of the experiment. NaOH waslater used for the second part of the experiment.The molar ratios used for this laboratory were stated as follow: For the first experiment,the calculations can be solved using the following molar ratios: Grams of KHP * (1 mol KHP/204.2 g KHP) * (1 mol NaOH/1 mol KHP) * (1/ volume in L used of NaOH). The volume usedof NaOH can be determined by subtracting the final minus initial volume (Volume used of NaOH= Final volume – initial volume).Also, the equation that was used to represent the titrationbetween a weak acid and a strong base was: HA + NaOHsalt (NaA) + H2O (at theequivalence point). Moreover, the percent error is used when comparing an experimental result
with a theoretical value that is the expected value. Percent error could be calculated at the end ofthe experiments using this formula: Percentage of Error: ((actual pKa– theoretical pKa)/theoretical pKa) * 100 (North Carolina State University, 2010).While it is true that there were two acid-base titrations in both experiments, they weredifferent from each other. During the first experiment, there was a change of color in the solutionin which a light pink color meant that the equivalence point was reached. On the other hand,during the second experiment, a pH meter was used to determine pH and create a graph thatdetermined the equivalence point and the base's molarity. A pH meter measures pH by addingsmall increments of the base to an acid solution to later create a graph made with pH along thevertical axis and volume of base added along the horizontal axis (Uniscie University, n.d)The titration curve which has five characteristics. First, the initial pH is higher than thetitration of a strong acid; second, the initial increase in pH at the beginning of the titration meansthat the anion of the weak acid becomes a common ion that reduces the ionization of the acid;third, the changes occur gradually after that first rapid increment because the solution acts as a

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Term
Spring
Professor
nan cao
Tags
pH, Sodium hydroxide

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