Question

Transition metals and complexes:

Dilute ammonia acts as a source of OH^-.

4 test tubes containing 1cm³ of Mn²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ solution were made up. Dilute ammonia solution was added slowly until the test tubes were half full. Obersvations were made on initial addition of NH₃ as well as any further reactions as more NH₃ was added.

a) For which metals does NH₃ appear to displace OH^- ? Can you relate this with their positions in the transition metal series?

Answer 1

Ni+2

by adding NH3 to Ni+ 2 solution intially it form Ni(OH)2 ( green coloue solid) and further addition of NH3 leads to the formation of Ni(NH3)6 complex which in blue colour

Ni⁺² + 2OH^- ----> Ni(OH)₂ ( s) : green clour solid

Ni⁺ + 6NH₃----> [Ni(NH₃)₆]⁺² : blue colour

Zn⁺²

intilaly Zn+2 forms zincate ion with OH-

Zn^{+ 2}+ 4(OH^-)---->[Zn(OH)₄]^-2

Zn⁺² + 4NH₃----> [Zn(NH₃)₄]⁺² ( COMPLEX ION)

Mn⁺²

Mn⁺² +2OH^-----> Mn(OH)₂ (s)

Cu⁺²

Cu⁺² + 2OH^- ----> Cu(OH)₂

Cu⁺² + 4NH₃----> [Cu(NH₃)₄]⁺² ( blue colour)

Copper metal displace OH ligand with NH3 , because NH3is strong feild ligand and OH is weak field ligand.