FeCl3 + CNS- ⇌ Fe(CNS)2+ + 3Cl-
mix equal amts of solutions of iron (III) chloride with potassium thiocyanate which forms CNS2+ which is red
add Cl- in the form of HCL. the system tries to reduce its conc by forming Fe3+ and CNS-
the Fe3+ makes the solution yellow
adding more Fe3+ in the form of FeCl3 to the mixture drives it to the right again
