colour changes of reactions in gcse chem

Hi, i noticed some past questions on colour changes in reactions e.g the reaction of anhydrous copper sulfate + water going from white to blue and anhydrous cobalt chloride going from blue to pink. Is this something we just need to memorise or is there a logic behind them i need to know? Thank you!!

Reply 1

B-elle

Original post by issyb_123

Hi!, I do A-Level chem atm and even at this level it's just something you need to memorise. When the salt is dissolved in water it separates (e.g. CuSO4) into the two ions Cu^2+ and SO4^2-. The colour of the copper ions in solution is blue, and cobalt ions are pink. So unfortunately that part of the gcse is a memory game, and each transition metal ion has its own colour in solution which is just how it happens to be. I hope this helped!