When excess of aq. KCN is mixed with aq. `CuSO_(4)` a complex named potassium tetra cyano cuprate (II) is formal
`4KCN_((aq))+CuSO_(4(aq))rarrunderset("Soluble")(K_(2)[Cu(CN)_(4))]_((aq))+K_(2)SO_(4)(aq)`
`rarr` The complex formation is due to the presence of strong ligands `CN^(-)`
