Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions. In double replacement reactions, the positive ions exchange negative ion partners. Many double displacement reactions occur between ionic compounds that are dissolved in water. A double replacement reaction is represented by the general equation.
AB + CD → AD + CB
In a double displacement reaction, atoms from two different compounds switch places. The reactants are two compounds and the products are two different compounds. For example:
Fe2O3 + 6HCl → 2FeCl3 + 3H2O
Double displacement reactions can be further classified as neutralization and precipitation reactions.
The acid-base reaction results in the formation of salt (neutral in nature) and water. For example
- On mixing an aqueous solution of hydrochloric acid with an aqueous solution of sodium hydroxide, sodium chloride and water are formed.
- HCl + NaOH → NaCl + H2O
In this reaction, the precipitate is formed in a solution or inside another solid during a chemical reaction.
- On mixing aqueous solutions of silver nitrate and sodium chloride, a white curdy precipitate of silver chloride is formed.
- AgNO3 + NaCl → AgCl + NaNO3
Application of double displacement reaction
- Acid indigestion
- Extraction of metals
- Flame photometry