Question

10) (3 pts.) List the progression of cobalt-doped, calcium sulfate-based dessicant colors from driest to most fully hydrated. What colors are the molecular sieves and the activated carbon? Do the molecular sieves or activated carbon change color?

Answer 1

Progression of the dessicant colors

• Most of the cobalt compounds are colour changing compounds with respect to temperatue and humidity.
• As the humidity increases the colour of the cobalt compound changes from skyblue to pink.
• This type of siginificant colour changing property of the cobal doped compounds such as cobalt chloride and calcium sulphate, make them useful as a humidity indicator in weather instruments.
• Cobalt doped paper is used to test for the presence of water leaking through tiny cracks in pipes or porcelain. When water is present, the test paper goes from blue to pink.
• As the humidity increases, and water is absorbed by Cobalt compound, the crystal structure rearranges for water molecules forming the dihydrate.
• As the humidity increases further, the crystal structure again changes, this time rearranging four more water molecules, forming the hexahydrate.

Colours of molecular sives and activated carbon

• Molecular sieve is a good desiccant available due to technical performance and its ability to adsorb moisture, in this case moisture, is so intense that it can remove trapped H20 molecules from a fully saturated silica gel bead, which in turn changes the silica gel back to its original Cobalt blue color.
• Activate dcarbon is mostly prepared from charcoal and hence has the colour of charcoal. It varies from ash colour to coke black.

Molecular sives made of cobalt doped material change colour due to the presence of moisture in the materials, where as activated carbon does not change its colour.