if I was asked to set up a procedure that will allow me to check the concentration of aqueous Co2+ ions in a reaction vessel every 15 mintues, what could I do to quickly and accurately determine the concentration of colbalt ions in the solution?
You might want to look at the color of Co(H2O)6 2+ or the Co(NH3)6 2+ ions. Here is a page that looks at those as well as some other reactions of Co^2+. Much of what you choose, of course, depends upon the concn of the cobalt ion.
http://www.chemguide.co.uk/inorganic/transition/cobalt.html