CH 204 Report #7 - CH 204 Introduction to Chemical Practice...

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CH 204 – Introduction to Chemical PracticeExperiment #7 – Strong Acid- Strong Base Titration INTRODUCTIONIn this experiment, the concentration of HCl was determined through a series of titrations using the strong base of NaOH. NaOH, standardized with KHP was used to titrate the HCl sample in order to calculate its exact concentration. All the while, pH of titrations were monitored using a pH probe and the pH indicator phenolphthalein.Specifically the analytical technique of titration was used in this experiment to quantitatively find the concentration of a species in a solution by reacting it with a second species ofa known concentration. In titrations of acids and 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 of the unknown can be calculated. 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 itby placing a clamp on the burette and a tip at the end in 1855.2The theory in titration is that either a pH probe or an indicator such as phenolphthalein will be used to signal to the experimenter that the endpoint has been reached. In fact pH probes can get even more specific than indicators, because the experimenter can continuously see the pH. These probes work using electrodes which recognize when there is an increase in hydronium ions by increasing voltage and they also recognize when there is an increase in pH corresponding with a decrease in voltage. Also it is important to note that the equivalence and endpoint typically do not coincide, so it is vital to choose an indicator that changes color close to the equivalence point. In this lab a lot of calculations were performed in the data analysis. Primarily the theoretical NaOH value was determined in order to estimate the endpoint. Once the data was collected the equivalence point was determined using a second derivative plot. Later for the standard solution the mass of KHP was divided by its molar mass to determine the moles of KHP. Using the moles determined, the molar ratio of NaOH to KHP, and the liters of NaOH the molarity of NaOH was determined for both runs. For Part B the liters of NaOH for both runs were determined and multiplied by the average molarity determined in Part A. This gives the moles of NaOH for both runs. These moles were then in turn multiplied by the 1 to 1 ratio of HCl to NaOH and divided by 0.005 L of HCl in order to get the molarity of HCl.

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