Determination of lead with standard potassium dichromate solution

25 DETERMINATION OF LEAD WITH STANDARD POTASSIUM DICHROMATE SOLUTION 

Both lead ion and dichromate ion yield a diffusion current at an applied potential to a dropping mercury electrode of —1.0 volt against the saturated calomel electrode (S.C.E.). Amperometric titration gives a V-shaped curve [Fig. 16.14 (C)]. The exercise described refers to the determination of lead in lead nitrate the application to the determination of lead in dilute aqueous solutions (10-3 — 10-4lVf) is self-evident. 

Reagents. Lead nitrate solution. Dissolve an accurately weighed amount of lead nitrate in 250 mL water in a graduated flask to give an approximately 0.01 M solution. For the titration, dilute 10 mL of this solution (use a pipette) to 100 mL in a graduated flask, thus yielding a ca 0.001 M solution of known strength. 

Potassium dichromate, ca 0.05M solution. Use the appropriate quantity, accurately weighed, of the dry solid. 

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