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By: Howard Andres In this experiment, our lab group’s purpose was to standardize a basic solution of NaOH, and then determine the equivalent mass of an unknown acid. In order to do this, the basic solution of NaOH was titrated with already standardized HCl solution. Then the unknown acid was placed into a solution with distilled water and then titrated to standardization with the now standardized NaOH solution. Using qualitative and quantitative information that we would find during the experiment, we would be able to find the equivalent mass of the unknown acid. In order to determine the progress of the standardization of the NaOH, we used phenolphthalein as an indicator. Slowly at first, and then increasing for longer intervals, a light pinkish color would form when a drop of NaOH would hit the solution of HCl and distilled water. Eventually the pinkish color stayed for thirty seconds, meaning that the solution was titrated to a standardized NaOH solution. Then, when the solid acid was placed into dissolved water, the white, powdery acid dissolved completely, and we were able to titrate it in the same way as the NaOH was standardized, carefully placing drop after drop until a pink color remained for thirty seconds. Our group was able to have two trials of standardizing the NaOH solution, and one trial of trying to obtain the equivalent mass of the unknown acid. Using the information received from the experiment, the molarity of the NaOH was found to be an average of 0.0999 M, and the equivalent mass of the unknown acid to be 79.4 g. There probably had been several possible errors in the course of out experiment which may have affected our results. One possible error is that we may have read the burets slightly incorrectly. This would then affect the volume that we would have of the NaOH, HCl, H+, or OH-, which would thereby affect their molarities. Those possibly incorrect molarities would then be used in order to obtain the equivalent mass of the unknown acid, meaning that mass would also be slightly off. Another possible error that there may be is that the phenolphthalein may not be completely neutral, but rather slightly acidic or basic. As a result, the standardized solutions may not really be standardized, since the pink color may only stay for at least thirty seconds if it was on the slightly acidic or basic side, meaning too much or too little of titrate was used; thus, the same things that as described earlier would be affected, volumes, molarity, and mass. We could only assume that the solutions were standardized. Overall though, the experiment went pretty well.
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