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Ion Exchange Reactions

Ion Exchange Reactions

Ion exchange reactions can be represented by:

\[\text{AB (aq)} + \text{CD (aq)} \rightarrow \text{AD} + \text{CB}\]

Either AD or CB may be a solid or a gas. When a solid forms this is known as a precipitation reaction. If a gas is formed then this may be called a gas forming reaction. Acid-base reactions are a special class of ion exchange reactions and we will look at them separately.

The formation of a precipitate or a gas helps to make the reaction happen. We say that the reaction is driven by the formation of a precipitate or a gas. All chemical reactions will only take place if there is something to make them happen. For some reactions this happens easily and for others it is harder to make the reaction occur.

Definition: Ion exchange reaction

A type of reaction where the positive ions exchange their respective negative ions due to a driving force.

Did You Know?

Ion exchange reactions are used in ion exchange chromatography. Ion exchange chromatography is used to purify water and as a means of softening water. Often when chemists talk about ion exchange, they mean ion exchange chromatography.

We have already looked at precipitation reactions.

Gas forming reactions

These reactions are similar to precipitation reactions with the exception that instead of a precipitate forming, a gas is formed instead. An example of a gas forming reaction is sodium carbonate in hydrochloric acid. The balanced equation for this reaction is:

\[\text{Na}_{2}\text{CO}_{3}\text{(s)} + 2\text{HCl (aq)} \rightarrow 2\text{CO}_{2}\text{(g)} + 2\text{NaCl (aq)} + \text{H}_{2}\text{O (l)}\]

Acid-base reactions

Acid-base reactions take place between acids and bases. In general, the products will be water and a salt (i.e. an ionic compound). An example of this type of reaction is:

\[\text{NaOH (aq)} + \text{HCl (aq)} \rightarrow \text{NaCl (aq)} + \text{H}_{2}\text{O (l)}\]

This is an special case of an ion exchange reaction since the sodium in the sodium hydroxide swaps places with the hydrogen in the hydrogen chloride forming sodium chloride. At the same time the hydroxide and the hydrogen combine to form water.

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