Pre-Assignments

1. What is the ratio of absorbance values for light absorbing samples slabs of width 2x, 3x and x?
2. Does the transmittance, T = I/I ₀ depend on the intensity of the incident light?
3. Say, you have used two transparent cuvettes of 1 cm edge length for the absorbance measurement of a sample. One cuvette is specially made with a central narrow slab for holding less volume of sample. Compare the absorbance values in both the cases.
4. If you plot absorbance values of the sample vs. path lengths for a particular wavelength for two different concentrations of a substance, where the concentration of one solution is double the other, what difference do you observe in your plot?
5. If absorbance is defined as, A = - log ₁₀ T, then what will be the expression of A in terms of % transmittance (%T)? [Hint: %T = 100 × T)

Post-Assignments

1. In actual measurements, the cuvette is filled to approx. two-third of its volume. What may happen if you take a very small quantity of sample solution, filling say, less than one-third of the cuvette volume?
2. Is the plot of absorbance values vs. path lengths for a particular wavelength always linear? Discuss your answer.
3. If you have a concentrated solution of a light absorbing substance, which path length cuvette – 1 mm or 10 mm – would you prefer for your measurement?
4. Can one use a reference cuvette (for blank) having path length different from the sample cuvette? Discuss your answer.
5. We know that A = (constant) × ℓ. The (constant) is the slope of the line obtained from absorbance vs. path length plot. Is the value of (constant) the same for all absorbance vs. path length plots? Why?