   Chapter 16, Problem 120SCQ

Chapter
Section
Textbook Problem

The nickel(II) ion exists as [Ni(H2O)4]2+ in aqueous solution. Why is this solution acidic? As part of your answer, include a balanced equation depicting what happens when [Ni(H2O)6]2+ interacts with water.

Interpretation Introduction

Interpretation:

[Ni(H2O)6]+2 in aqueous solution is acidic is to be stated and balance the chemical reaction between [Ni(H2O)6]+2 and water.

Concept introduction:

Metal cations interact with water molecules to form a hydrated complex. There is a formation of coordinate covalent bond between the metal cation and lone pair of electrons on the oxygen atom of each water molecule. A nickel ion, Ni+2 ion forms six coordinate covalent bonds to water.

Ni+2(aq)+6H2O(l)[Ni(H2O)]+2(aq)

Explanation

The structure of the [Ni(H2O)6]+2 complex is:

The lone pair on the oxygen forms coordinate bonds with nickel ion, which has an effect on the electrons in the OH bonds. These electrons get pulled towards oxygen even more that leaves the hydrogen nuclei more exposed than normal which makes the hydrogen atom more positive when they are attached to oxygen. The +2 charge is no longer located entirely on Nickel but spread over the whole ion- much of it on the hydrogen atoms.

The complex ion is acting as an acid by donating a hydrogen ion to water molecules in the solution. The first stage of this process is,

[Ni(H2O)]+2+H2O(l)[Ni(H2O)5(OH)]+(aq</

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