Determination of lead with standard dichromate solution:
The potential selected is -1.0 V vs SCE at which both lead ion and dichromate ions give diffusion current. Then, the graph acquired will be V shaped.
Reagents required: 0.001 M Pb(NO3)2 AR, 0.005 M potassium dichromate and 0.01 M potassium nitrate.
Procedure: To 25.0 cm3 of 0.001 M Pb(NO3)2 solution in the cell, add 25 cm3 of 0.01 M potassium nitrate solution as supporting electrolyte and pass N2 for 15 minutes. Apply -1.0 V vs SCE and make necessary connections on the polarograph. Add 0.005 M dichromate solution from the microburette in 0.5 cm3 portions and pass N2 each time for 1 minute. Remember down the readings of the burette and the galvanometer. Initially the current due to Pb2+ decreases as dichromate added and increases after the end point with excess dichromate. As follows making volume corrections draw the graph and remember down the last point reading. Repeat this along with unknown Pb(NO3)2 given.