why insolube AgCl is soluble in ammonia solution and sodium thiosulfate solution?

Question

why does the colour of Co^2+ in aq. solution change on adding HCL?

why does colour of Fe^3+ change in presence of NCS-?

Answer 1

Because Ag+ forms a complex ion, Ag(NH3)2+, whose Cl- salt is soluble. Likewise Ag(S2O3)-

Co(H2O)6, the usual ion in water, adds Cl- ions to form a complex ion as high as CoCl6 4-, which is a different color.

Fe 3+ forms complex ions as high as Fe(SCN)6 3-, which is brilliant red.