Complex ions for NCEA Level 2

1. You will be given a list of possible complex ions in your resource sheet. However, they are quite easy to learn.

2. Complex ions are written in square brackets and have a charge. They are always solutions, and so have the state symbol (aq).

3. Complex ions that you will come across are formed by the addition of:

• excess sodium hydroxide - which have OH^- ligands (usually four)

• excess ammonia solution - which have NH₃ ligands (usually four)

• potassium thiocyanate solution - which has one SCN^- ligand.

4. Apart from complex ions formed with a central Ag⁺ or Fe³⁺ ion, all complex ions have four ligands.

5. The complex ion with a central Ag⁺ ion has two NH₃ ligands - [Ag(NH₃)₂]⁺. It has this + charge as ammonia is neutral and the silver ion has a + charge.

6. The complex ion with a central Fe³⁺ ions has one SCN^- ligand - [FeSCN]²⁺. It has this 2+ charge, as the Fe³⁺ ion has a 3+ charge and the SCN^- ion has a 1- charge.

7. The other complex ions are listed below. Their charges can be calculated by finding out the sum of the charges in the complex ion:

• [Cu(NH₃)₄]²⁺

• [Zn(NH₃)₄]²⁺

• [Zn(OH^-)₄]^2-

• [Pb(OH^-)₄]^2-

• [Al(OH^-)₄]^-