CHEMISTRY 1b, SPRING, 2005, PROBLEM SET II
1) Anhydrous solid manganese(III) chloride is very dark violet whereas the solid tetrahydrate,
e.g. MnCl24H2O is light red.
N. B. The chloride anions in the crystal can serve as ligands and the formula of the tetrahydrate is
better given as [Mn(H2O)4Cl2]Cl.
a) Provide an explanation for the striking changes which occur when the anhydrous salt is
hydrated to form the tetrahydrate.
b) Predict what changes will occur when the anhydrous salt is exposed to vapors of
ammonia.
2) 50 ml of aqueous 0.1 M cobalt(II) nitrate was prepared.
a) Predict the structure of the complex species in the solution. What is the ligand?
b) What is the hydridization of the cobalt ion?
c) How many bonding molecular orbitals are occupied? how many non-bonding? how
many anti-bonding?
3) In the synthesis of hexaämminenickel(II) chloride, concentrated 15 M aqueous ammonia is
added to an aqueous solution of nickel(II) chloride. The sample is washed with small portions of
ether and is stored in a closed vial.
a) Compare the color of the aqueous solution before and after the addition of the
ammonia.
b) Predict the number of unpaired electrons in the product.
c) How many bonding, non-bonding, and antibonding molecular orbitals are occupied in
the product?
d) Why is concentrated ammonia used rather than dilute ammonia? What would happen
to a sample of the complex left in an open bottle?
f) Suppose a 50-50 mixture of methylamine, CH3NH2, and ammonia were used instead of
pure aqueous ammonia. Give the formulae and draw the structures of all the species
which could be formed. Where isomers are possible, give the structures of all the
isomers.
4) Predict the crystal structures of lithium oxide, manganese(II) selenide, and calcium oxide.
Provide a full description including the coordination numbers of the cations and anions. Use the
ionic radii in Figure 17-12 on page 743 of Oxtoby. These values are very close to those proposed
by Linus Pauling in his classic monograph The Nature of the Chemical Bond. One required
datum is missing in the figure, r(Mn+2) = 0.80 Å.
5) Use the data provided in Problem 48 in Chapter 14 of Oxtoby. As instructed in the problem,
calculate values for Ea and A. That is, perform an Arrhenius analysis of the data. Also obtain
values of the enthalpy and entropy of activation from an Eyring analysis, i.e. a plot of
Rln[hk/kBT] versus 1/T.
problemset2_2005.doc, WES, 9 Jan. 2005