I have combined the cobalt system A3 posters with two worksheets that students can fill in when they explore this system in class. Print them off in colour, get the students to use coloured pencils to fill it out to emphasise the coloured complex ions.
 
This pack contains
A3 Poster Cobalt chloride system (concentration changes)
A3 Poster Cobalt chloride system (temperature changes)
Student worksheet for each A3 poster with answers
 
The posters are A3  in size which were designed for printing and laminating. Great for display on walls, A3 laminated cards for group work to examine while completing worksheets etc. Maybe print them as an A4 size or A5 for a summary book.