Sulfate ion can be determined by an amperometric titration procedure using Pb2+ as the titrant. If the potential of a rotating mercury film electrode is adjusted to -1.00 V versus SCE, the current can be used to monitor the Pb2+ concentration during the titration. In a calibration experiment, the limiting current, after correction for background and residual currents, was found to be related to the Pb2+ concentration by i1 = 10cPb2+ where i, is the limiting current in mA and CPb2+ is the Pb2+ concentration in mM. The titration reaction is
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If 25 mL of 0.025 M Na2SO4 is titrated with 0.040 M Pb(NO3)2, develop the titration curve in spreadsheet format and plot the limiting current versus the volume of titrant.