Normal Pulse Polarography Determination of Lead, Cadmium and Zinc Essay
Normal Pulse Polarography Determination of Lead, Cadmium and Zinc Abstract- In differential pulse polarography, it creates a continuous and constant rectangular voltage pulses that reside on a negative voltage ramp that is applied by the indicator electrode; where the current is measured before and near the end of each square wave. However in Normal Pulse Polarography, it is measured differently, where the rectangular voltage potentials are increasing in increments and are not constant as compared to the DPP.
The voltages are not set upon an increasing voltage ramp, but the rectangular voltage potentials are held on the same constant value, made of short potentials that have small durations, but increasing incremental value. The graph is plotted current against the potential, where there is the limiting current, residual current, and the diffusion current for each metal present in the solution, and ultimately will represent a sigmoidal shaped graph.
The diffusion current will be used to calculate the peak current and be plotted against the concentration that peak current pertains to. The graph of peak against concentration will be used to find the unknown concentration sample. Data- -Graphs are attached to the lab report – Solutions were readjusted to 3. 0x10-5 M, 1. 0x10-5 M, 5. 0x10-6 M -Drop time was adjusted to . 5 seconds -Purge Time- 300 seconds Table 1. 1- Concentration and peak currents
|Concentration |Pb Current |Cd Current |Zn Current | |5. 00E-06 |1. 257 |1. 5801 |1. 2709 | |1. 00E-05 |5. 7892 |5. 3775 |6. 1752 | |3. 00E-05 |10. 935 |9. 6750 |10. 800 | |unknown |2. 1000 |1. 9800 |0. 0000 | Results- Figure 1. 1- Peak Current vs. Lead Concentration [pic] Figure 1. 2- Peak Current vs. cadmium Concentration [pic] Figure 1. 3- Peak Current vs. Zinc Concentration [pic]
-Calculation for each peak Current of each metal on every concentration are located on the graphs attached to the back. Unknown Solution Calculation- -Lead( y=350026x + 0. 7433 Peak current- 1. 98 µA 2. 1=350026x + 0. 7433 Unknown lead concentration= 3. 53×10-6 M -Cadmium( y=292676x + 1. 1541 Peak Current- 2. 1 µA 2. 1= 292676x + 1. 1541 Unknown Cadmium Concentration= 3. 23 x 10-6 M -Zinc- Unknown Zinc Concentration- There is no diffusion current on the graph and in the area pertaining the range of zinc, concluding that there is no zinc in the solution.