1.How is the 0% T set in the Spec 20? What happens to the light beam when this c
ID: 1084146 • Letter: 1
Question
1.How is the 0% T set in the Spec 20? What happens to the light beam when this control is being adjusted? How is the 100% T set in the Spec 20? What happens to the light beam when this control is being adjusted?
2.When the wavelength selector control is being adjusted in the Spec 20, what is physically occurring in the instrument? Describe how adjusting this control changes the wavelength of light passing through the sample cell.
3.The Beckman DB is a double-beam in time instrument; however, its simple configuration closely resembles that of a single-beam instrument. Describe how its double-beam-in-time configuration works.
4.What is the predominant color emitted by tungsten lamp in the Spec 20? What color is the phototube most sensitive to? What color is the Spec 20 most responsive to? What is the optimum wavelength range for operation of this spectrometer? Justify your answers.
5.From your results, explain why it is necessary to readjust the 100% T every time the wavelength is changed in the Spec 20. Explain how the difference in the instrument response as a function of wavelength is compensated for in a double-beam instrument.
6.If a Spec 20 is going to be used routinely at wavelengths above 600 nm, a different phototube is needed. Explain why this might be necessary and what the characteristics of this new phototube might be.
7.When a solution appears to be red in color, does the solution absorb or transmit red light strongly? Explain.
8.Is the plot you made of A vs. c for the chromium nitrate solutions linear throughout the entire concentration range (0 M to 0.350 M)? If not, suggest reasons for the nonlinearity.
9.What range of chromium nitrate concentrations can be determined with your calibration curve? Explain.
10.Compare the spectra obtained with the two spectrometers. Comment on their similarities and differences. The bandwidth of the Spec 20 is 20 nm and that of the double-beam instrument is 2 nm. Do you see any effect from this difference in the two spectra? Explain.
Explanation / Answer
ANSWER 1 :
The 0% T is set in the Spec 20 with the cuvette chamber empty, set zero %T using the left hand knob.
A small door closes and blocks out all light from the source. There is now no transmission of any light and therefore Transmission = 0
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