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 i_l = 10 cPb²⁺, where i_l is the limiting current in mA and cPb²⁺ is the Pb²⁺ concentration in mM. The titration reaction is

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.

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Sof + Pb?+ = PbSO,() K = 1.6 x 10-8 %3D