Q.Give one test to differentiate [Co(NH₃)₅Cl]SO₄ and [Co(NH₃)₅SO₄]Cl.

Step 1. [Co(NH₃)₅Cl]SO₄ and [Co(NH₃)₅SO₄]Cl are ionisation isomers (Section 5.5.1.3): the first has Cl⁻ bound inside the coordination sphere and SO₄²⁻ as the free, ionisable counter ion; the second has SO₄²⁻ bound inside the coordination sphere and Cl⁻ as the free counter ion.

Step 2. Adding BaCl₂ solution tests for free SO₄²⁻: [Co(NH₃)₅Cl]SO₄ gives an immediate white precipitate of BaSO₄, since its sulfate is free in solution and can react with Ba²⁺; [Co(NH₃)₅SO₄]Cl gives NO precipitate with BaCl₂, since its sulfate is locked inside the coordination sphere and unavailable to react. …

Recognise the pair as ionisation isomers and pick a precipitation test (BaCl₂ for free sulfate, or equivalently AgNO₃ for free chloride) that reacts only with whichever ion h …

• Trying to distinguish the two by a colour difference rather than a precipitation test -- the differentiating feature here is which ion is free in solution, best probed chemically. …