Edexcel IAL Chemistry 17.12 H2O, OH- and NH3 as monodentate ligands

For monodentate ligand questions, state both parts: one lone pair is donated and only one coordinate bond forms to the central metal ion.

Exam points

Explain monodentate as forming one dative bond through one donated lone pair.
Recognise H2O, OH- and NH3 as electron-pair donors in complex-ion formation.
Write complex formulae such as [Fe(H2O)6]2+ when monodentate ligands surround Fe2+.

[Maximum number: 2]

This question is about compounds and complex ions of iron.

In aqueous solution, iron(II) exists as the complex ion $\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ .

Explain how water acts as a monodentate ligand.

An explanation that makes reference to the following points:

- because it forms one dative (covalent) / co-ordinate bond (to $\mathrm{Fe}^{2+}$ )

(1)

- using a lone pair (of electrons) on oxygen

(1)

Allow 'a dative/co-ordinate bond'

Allow oxygen donates a pair of electrons Ignore water uses a lone pair of electrons COMMENT

Allow M2 for a diagram showing the oxygen lone pair forming the co-ordinate bond but annotation needed to score M1

(2)

Number

Admer

T

All question bank results loaded

17.12—H2O, OH- and NH3 act as monodentate ligands question 1