Ion Concentrations

I. Dissociation

                A. Ionic compounds are made up of 2 parts

                                a. Cation: positively charged particle

                                b. Anion: negatively charged particle

                B. When ionic compounds are dissolved in water the cation and anion separate from each other. This process is called dissociation

                C. When writing dissociation equation the atoms and charges must balance

                                a. The dissociation of sodium chloride is:

                                NaCl ---> Na⁺ + Cl^-

Ex. Complete the following dissociations

1. Fe(OH)₂ ---> Fe²⁺ + 2OH^-

2. Na₃PO₄ ---> 3Na⁺ + PO₄^3-

3. Fe₃(PO₄)₂ ---> 3Fe²⁺ + 2PO₄^3-

                        D. If the volume does not change then the concentration of individual ions depends on the balanced coefficients in the dissociation equation

Ex. Determine the [Na⁺] and [PO₄^3-] in a 1.5M solution on Na₃PO₄

Na₃PO₄ -->  3Na⁺ + PO₄^3-

1.5M x (1/1) = 1.5M [PO₄^3-]

1.5M x (3/1) = 4.5M [Na⁺]

Ex. Determine both ion concentrations when a 2.5M solution of Lithium sulphate dissociates.

Li₂SO₄ ---> 2Li⁺ + SO₄^2-

2.5M x (2/1) = 5.0M [Li^-]

2.5M x (1/1) = 2.5M [SO₄^2-]