In experiment V, “ISE: The Determination of Chloride”, the concentration of an Unknown Chloride solution, and the Wt% of NaCl in a sample of celery salt, were both determined. To determine the concentration of an Unknown Chloride solution, a Calibration plot is first prepared.
The Calibration plot is made by first measuring a series of known concentrations of Cl- (with the same activity of the unknown solution) and obtaining a set of E-values for these standards -A graph is then plotted from the corresponding E-values vs. the logarithm of the concentration of Cl-. Once all the data points have been plotted, the slope of the line is determined (found by using a least squares …show more content…
In potentiometric titrations with ISE electrodes, the activity of the solution will ultimately contribute in the determination of the known concentration. The possibility added activity via introduction of water may contribute to a falsely high concentration.
Possible systematic errors that could have happened (not throughout my analysis however) if:
a. After you dried your unknown, but before you were able to weigh it, you left it out of the desiccator and it picked up moisture from the air. If this where to happen and if some moisture was taken up by my unknown sample it could throw off the concentration as well as Wt% of the unknown. If the unknown sample had picked up moisture from the air and been weighed, then the weight of that sample would contain less of the actual unknown. Being that the weight of the sample is greater than that of the actual mass of the of the pure unknown weight (without water) that should be acting in the solution, then when calculating the concentration and wt% of the unknown, the values will surely be off. Taking into consideration that we depend on the fact that, it is presumed that the activities of both solutions are roughly the same, we could not accurately calculate the concentration nor Wt% otherwise. The added activity from the water impurities will have a direct effect on the potential of the cell; given that there is an increase in the activity of ions, the potential readings of the solution will be falsely higher than if there was no added activity. The falsely high activity of the unknown solution will cause a falsely high calculation in both concentration and Wt% of