Download PROBLEM SET I

PROBLEM SET I
CHEMISTRY 1b (Steinmetz), SPRING, 2007
1) A 1.0 x 10-4 M solution of an absorbing compound, e.g. benzene, is placed in a rectangular
cuvette with a path length of 1.0 cm. The absorbance of the solution is found to be 1.0.
a) Calculate the compound's molar extinction coefficient, .
b) What fraction of the incident light exits the cuvette?
d) Calculate %T if the concentration is doubled.
2) Determine the following quantities for a Li+2 ion in a 4f state:
a) its energy
b) its ionization energy
c) its rms (root mean square) radius
d) its orbital angular momentum, L, in units of h/2π
e) its degeneracy, i.e. the number of distinct quantum mechanical states that have the
same energy AND values of n and l
f) the number of different wavelengths of light emitted by a population of these excited
species. Give the initial and final values of n for each transition.
3) Draw the Lewis electron-dot structures of the 5 isomers of C2H5N. Predict the bond angles in
each isomer. None of the structures will have atoms with formal charge.
4) Consider the hydrocarbon allene which has the structural formula H2C=C=CH2.
a) Draw the Lewis dot structure of allene.
b) Determine the hybridization of all atoms.
c) Provide a description of each unique bond in the molecule. Use the σ, π formalism.
d) Is allene completely planar? Support your answer with a short discussion.
5) Draw the Lewis-dot structures of 4 structural isomers of C3H4O. Are any of your isomers
planar? Discuss why. Would MO theory provide a better treatment of any of your isomers?
Discuss why. Provide the following information for each isomer.
a) the hybridization of the heavy atoms
b) estimates of the bond angles
c) a description of the bonds between the heavy atoms.
6) Consider the structures of methane (CH4) and chloroform (CHCl3).
a) Which molecule has a rotational (microwave) spectrum? Why?
b) The atmospheres of the outer planets have a high concentration of methane. Would
the presence of methane prevent mapping the surface of these planets with radar?
Explain.
c) Which molecule has an infrared spectrum? Explain why.
7) The conformers of 1,2-difluoroethane, the structural isomer of C2H4F2 in which the fluorine
atoms are on separate carbon atoms, were discussed in class. Which conformer the anti (s-trans)
or the gauche, has a microwave spectrum? an infrared spectrum? an electronic spectrum?
Explain. What chemical information can be obtained from the spectra?
PSI_S05.doc, 5 Jan. 2005, revised 3 Jan. 2007 WES