Turn on thread page Beta

Ligands confusion watch

    • Thread Starter

    Hi! So i´m preparing for the Chemistry A2 exams and i have a doubt: If OH- and NH3 act as bases and deprotonate hydrated d block ions, why isn´t OH- considered a ligand as well? Why the reaction with excess ammonia with these hydrated d block ions results sometimes in what is called ligand exchange? So, when do i name a reaction as ligand exchange and when as acid base? Please i am quite confused, i would be really grateful for your help.

    It is a ligand.

    The O has a lone pair, with which it can form coordinate bonds.

    If OH- deprotonates a water, it leaves behind an OH- attached to the central ion. It might not be actually substitution, but the end result is much the same.

    You could get asked to show when NH3 acts like a bronsted lowry base, this is when it accepts a proton.
    Co(H2O)6]2 + 2(NH3) = Co(H2O)4(OH)2 + 2(NH4+)

    or when it acts like a Lewis base, when it donates an electron pair-This is when NH3 acts like a ligand, as it donates its lone pair to form a coordinate bond with the metal ion.
    Co(H2O)6]2 + 6(NH3) = Co(NH3)6 + 6(H2O)

    you just have to learn that NH3 only acts as a lewis base and does a ligand exchange with the 3 metal ions (Cu, Co, Cr) and that Cu doesnt loose all of its water ligands.
Submit reply
Turn on thread page Beta
Updated: May 11, 2014

University open days

  • University of East Anglia
    All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
    Wed, 30 Jan '19
  • Aston University
    Postgraduate Open Day Postgraduate
    Wed, 30 Jan '19
  • Solent University
    Careers in maritime Undergraduate
    Sat, 2 Feb '19
Brexit: Given the chance now, would you vote leave or remain?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.