Visible Spectrophotometric Analysis of Cobalt and Nickel
Understand the function of the Spectronic 20 Spectrophotometer, the Perkin-Elmer recording UV-visible spectrophotometer and reveal the concentrations of nickel and cobalt in an unknown solution. Procedure
In the Lab: Part B: Complex Formation
Pipette 20mL aliquots into a 150mL beaker. Do the same with cobalt nitrate and nickel nitrate. Add between 0.70g and 0.90g of EDTA to each of the cobalt nitrate and nickel nitrate. Add 1.5g of EDTA to the unknown. Pipette 10mL of ph10 buffer into each beaker. Cover the beakers with watch glasses and warm on low for an hour to complete the formation of the complex. Transfer the solutions to a 50mL volumetric flask and dilute to the mark with deionized water. Prepare a blank solution containing 3mL of buffer and 0.40g EDTA in a 25mL solution. On the Spectronic 20:
Turn to 510nm with the wavelength selector. Fill a cuvette with deionized water and wipe the outside of the cuvette. Insert the cuvette on the Spectronic 20. Set 100% T. Without readjusting the control, take readings from the %T scale at the wavelengths from 350nm to 600nm, with 15nm intervals. Plot a response curve of %T vs. wavelength (nm). Observations
When mixing the solutions and placing them on the hot plate, color differences were found. The colors became brighter; such as for cobalt a bright pink color, for nickel a green/blue color that later on turned into bright blue as the NiNO3 dissolved and heated. The unknown from being a light pink turned purple as the EDTA was added. The solvents all dissolved in less than an hour and a half. The heating started at 2:15pm and was taken out at about 3:10pm. When working with the Spectronic 20, it was noticed that the numbers jumped around a lot while trying to find the point at which the instrument was most responsive. The readjusting seemed difficult yet after a couple of tries it started working accordingly. Calculations...
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