Question

why would HCl be an inappropriate solvent to elute Cr(III) complexes from a column during ion exchange chromatography?

Answer 1

H⁺ is a monopositive Ion and thus can't replace the strongly bound tripositive Cr^{​​​​​3+} Complexes. To elute Cr^{​​​​​3+} Complexes, A Harder tripositive ion(such as Al^{​​​​​3+}) is needed. This is the main reason, for what any Acid is inappropriate to Elute the Cr^{​​​​​3+} Complexes, during Ion Exchange Chromatography.

Also, In presence of HCl, Cr(III) Complexes can undergo Nucleophilic Substitution by Cl^​​​- , thus the Complex breaks in Presence of HCl. That's why HCl is an inappropriate solvent to Elute Cr(III) Complexes, during Ion Exchange Chromatography.