Nonmetals with Anions
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Reaction Between Nonmetals and Anions

We are not limited to metals when dealing with redox reactions. Let's look at the reaction of a nonmetal with an anion to show what can happen on the other side of the periodic table.

Bromine and Iodide

Here are the the chemicals for this example: aqueous sodium iodide solution containing I- in the bottle and molecular bromine (Br2) dissolved in some carbon tetrachloride in the tube.

Sodium iodide solution and bromine.
At the beginning of the reaction (left) the red Br2 is dissolved in the nonpolar carbon tetrachloride layer at the bottom of the tube and I- is in the water layer on top. After the reaction (right) the purple color of I2 can be seen in the nonpolar carbon tetrachloride layer at the bottom of the tube.

Reaction of iodide with bromine - start.

 Reaction of iodide with bromine - after.
The unbalanced equation for this reaction can be written in this way.

Br2 + NaI rtarrow.gif (850 bytes) I2 + NaBr
Because the sodium ions are spectator ions they can be removed from the equation to show what is happening to the bromine and iodine.

Br2 + I- rtarrow.gif (850 bytes) I2 + Br-

We can dissect this equation and write separate balanced half-reactions for the bromine and the iodine.

Br2 + 2 e- rtarrow.gif (850 bytes)  Br-

2 I- rtarrow.gif (850 bytes) I2 + 2 e-

These half reactions can be added together to give the balanced equation for this redox reaction.

Br2 + 2 I- rtarrow.gif (850 bytes) I2 + 2 Br-

Note that in these reactions with nonmetals the change from atom to ion is reduction, whereas with metals the change from atom to ion is oxidation. That is an important difference between metals and nonmetals.

 

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