Question

The reaction in which ions in the reactants are exchanged to form a precipitate is called as ...................... reaction.

• A. Combination
• B. Decomposition
• C. Displacement
• D. Double Displacement

Hint:

Double displacement reactions are important in analytical chemistry for identifying unknown compounds through precipitate formation. These reactions are also essential in water treatment processes, where unwanted ions are removed.

Answer 1

The Correct Option is D

A double displacement reaction, also called a double replacement reaction, occurs when two ionic compounds in aqueous solution exchange ions to form new compounds. This type of reaction involves the replacement of one element in each compound by another. If one of the products is insoluble in water, it will form a precipitate.
In a double displacement reaction, the positive and negative ions of two ionic compounds swap places, resulting in the formation of two new compounds.
One of these new compounds, typically a salt, may not dissolve in water, thus forming a solid precipitate.
A classic example is when solutions of silver nitrate (AgNO$_3$) and sodium chloride (NaCl) are mixed. Silver chloride (AgCl), a white precipitate, forms because it is insoluble in water.
This reaction can be summarized as follows: \[ \text{AB}(\text{aq}) + \text{CD}(\text{aq}) \rightarrow \text{AD}(\text{s}) + \text{CB}(\text{aq}) \] Where "s" denotes the solid precipitate, and "aq" denotes an aqueous solution.