What Is The Name Of Cocl4 2-?

CoCl4 2- is the result of adding hydrochloric acid to a water-based solution of cobalt chloride, and is also known as cobalt tetrachloride.

Cobalt tetrachloride is of limited practical use, and is normally used only in experiments to demonstrate Le Chaterlier's Principle of the redistribution of ion concentration once the equilibrium of a substance or solution has been subject to an external reaction.

Uses for Cobalt Chloride (CoCl2)

Outside the laboratory, the main use of cobalt chloride is as a humidity indicator, making it useful for equipment used to forecast and measure weather conditions. Cobalt chloride changes color when humidity increases, starting as a blue substance, then changing from purple, then pink when very humid. 

This is because the chloride molecules have to 'make room' for the absorbed water around the central cobalt molecule.   

Here's an experiment showing how cobalt chloride can be used to demonstrate Le Chatelier's Principle: