A double displacement reaction is also known as double replacement reaction or salt metathesis reaction. It is a chemical reaction in which two compounds react where the positive ions (cations) and the negative ions (anions) of the two reacting compounds switch places to form two new compounds or products. This is exactly like how you go for a dance and with change of music, you tend to switch partners.
The general equation for the double displacement reaction is- A+B– + C+D– ⇾ C+B– + A+D–
The resulting bond between the two reactants can either be an ionic bond or a covalent bond. Normally, these reactions yield the precipitation of a product.
This type of reaction is not typically about swapping since in swapping, you end up having the same substance that you started with. The solvent for the double replacement reaction is water while the reactants and products are ionic compounds or acids or bases.
For example, BaCl2 (aq) + Na2SO4 (aq) ⇾ BaSO4 (s) + 2 NaCl (aq)
TYPES OF DOUBLE DISPLACEMENT REACTION
- Counter-ion exchange
For exchanging counter ions, salt metathesis is a technique that is used. From an aqueous solution made of inorganic anions, salt metathesis reaction can be used to isolate the salts which are soluble in the organic solvents.
Example, NaReO4 + N(C4H9)4Cl ⇾ N(C4H9)4[ReO4] + NaCl
The metal complexes get alkylated in this reaction. The salt product usually precipitates from reaction solvent.
Example, (C5H5)2TiCl2 + 2 ClMgCH3 ⇾ (C5H5)2Ti(CH3)2 + 2 MgCl2
- Neutralization reaction
In this type of reaction, acid-base reaction occurs owing to the fact that an equal quantity of acid reacts with the equal quantity of base. This acid-base reaction yields in the formation of a salt which is neutral in nature along with water.
Example, HCl (aq) + NaOH (aq) ⇾ NaCl (aq) + H2O (l)
During a chemical reaction, when a solid gets formed in a solution or inside another solution, it is known as precipitation. This happens when the solubility product is lesser than the concentration of the dissolved ions.
Example, BaCl2 (aq) + CuSO4 (aq) ⇾ BaSO4 (s) + CuCl2 (aq)
- Double Decomposition
There is no need for the reactants to be dissolved.
Example, Ba(OH)2 + 2 CuCNS ⇾ Ba(CNS)2 + 2CuOH
- Acid and carbonates
In this, there is a reaction that takes place between an acid and a carbonate or bicarbonate. This type of reaction always yields carbonic acid which again decomposes into carbon dioxide and water.
Example, CH3COOH + NaHCO3 ⇾ CH3COONa + CO2 + H2O