HW 3 Inorganic Materials
Chemistry
Name:
Points: C7780 Date:
Max. 100 points Fall 2014 A
1. (20 pts) Mixed metal oxides could be prepared by sol-gel reactions from aqueous solutions of
metal salts.
a) (10 pts.) Order these ions Al3+
, Ba2+
, Cs+
, H+
, Li+
, Mg2+
according to the increasing value
of hydration enthalpy: Mz+
+ n H2O  [M(H2O)n]z+
Hhydration
b) (10 pts.) For a hydrolytic reaction [M(H2O)N]z+
+ h H2O  [M(OH)h(H2O)N-h](z-h)+
+ h H3O+
Hº
= (75.2 – 9.6 z) kJ mol-1
and Sº
= (– 148.4 + 73.1 z) J K-1
mol-1
Write equation that gives a measure of spontaneity of reaction. (Write a formula relating this
function to Hº
and Sº
). Calculate, for which of the above listed ions is this reaction
spontaneous?
2. (20 pts) Green light-emitting diodes can be made from solid solution of GaP and AlP. These
two compounds have band gaps of 2.26 and 2.43 eV, respectively. What composition would be
needed to prepare Ga1xAlxP with emitted light wavelength of 520 nm? Band gap varies linearly
with composition. Name the law governing this case.
1 eV = 1.602 1019
J. Show your calculation.
3. (20 pts) Mesoporous material MCM-41 consists of regular cylindrical pores of uniform
diameter. Relate its total pore volume Vp to its surface area SA and pore radius r.
4. (20 pts) Alkaline precipitation method for the preparation of mixed ferrites (MnxZn1x)Fe2O4
presents difficulties due to the varying solubilities of the metal hydroxides. Fe(OH)3 starts to
precipitate early at pH 2.6, while Mn(OH)2 precipitates at a much higher pH of 9.4. The Zn2+
cations precipitate at pH 7.6, but begin to redissolve at pH 9.
a) Write chemical equations for the precipitation and dissolution of Zn2+
cations.
b) What pH should be used to obtain homogeneous precipitate of mixed hydroxides?
5. (20 pts) What is the relation between the diameter of a spherical nanocrystal (Dc, large
spheres) and the size of tetrahedral pores (Dp, small sphere). Nanocrystals touch each other, they
are close packed. Show your calculation.