Problem 1
What are the relative energies of transitions observed in vibrational, rotational, electronic and nuclear magnetic resonance spectroscopies?
Problem 2
Convert the wavelengths (a) \(500 \mathrm{nm}\) and (b) \(225 \mathrm{nm}\) to \(\mathrm{cm}^{-1}\) (wavenumbers) (c) Do these wavelengths fall in the visible region?
Problem 3
(a) A solution of a compound X gives an absorbance reading of \(0.446 .\) What is the percentage transmittance \((\% T) ?\) (b) The transmittance for another sample of \(\mathbf{X}\) is \(70.9 \%\) To what absorbance reading does this correspond?
Problem 4
Aqueous solutions of \(\mathrm{Ni}^{2+}\) ions appear green. What is the approximate wavelength of light absorbed by aqueous \(\mathrm{Ni}^{2+}\) ions?
Problem 5
The absorption spectrum of benzene dissolved in cyclohexane contains bands at 183,204 and \(256 \mathrm{nm}\) (a) Which band corresponds to the lowest energy transition? (b) Which band corresponds to the lowest wavenumber? (c) For \(\lambda=256 \mathrm{nm}\) \(\log \varepsilon=2.30 .\) Determine the concentration of a solution (path length \(=1.00 \mathrm{cm}\) ) which gives an absorbance of 0.25
Problem 7
Solutions of azulene (11.4) in cyclohexane absorb at \(357 \mathrm{nm}\) and the value of \(\varepsilon\) for this absorption is \(3980 \mathrm{dm}^{3} \mathrm{mol}^{-1} \mathrm{cm}^{-1} .\) Such a solution contained in a cell of path length \(1.0 \mathrm{cm}\) gives an absorbance of \(0.58 .\) What is the concentration of the solution?
Problem 8
The absorption spectrum of a \(5.00 \times 10^{-4} \mathrm{mol} \mathrm{dm}^{-3}\) solution of azulene in cyclohexane in a cell of path length \(0.50 \mathrm{cm}\) shows an absorption with \(A=0.995 .\) Calculate the corresponding extinction coefficient.
Problem 9
Solutions of naphthalene in ethanol absorb at \(\lambda=312 \mathrm{nm} .\) A \(2.50 \times 10^{-3} \mathrm{mol} \mathrm{dm}^{-3}\) solution gives an absorbance of \(0.72 .\) Determine the concentration of a solution for which the absorbance is \(1.00 .\) The same solution cell was used for both readings.
Problem 10
Two solutions, I and II, of the same compound, in the same solvent and contained in identical solution cells are of concentrations \(5.00 \times 10^{-3}\) and \(1.75 \times 10^{-3} \mathrm{mol} \mathrm{dm}^{-3} .\) What is the ratio of their absorbances?
Problem 11
The compound \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) absorbs at \(\lambda=418 \mathrm{nm}(\log \varepsilon=3.01) ;\) experiments are carried out in a cell of path length \(1.00 \mathrm{cm}\) (a) Determine the absorbance of a solution of concentration \(6.0 \times 10^{-4} \mathrm{mol} \mathrm{dm}^{-3} .\) (b) What is the absorbance if the concentration is halved?
