Double-replacement reaction, or "metathesis" is a chemical reaction on the bio-molecular level. This article offers a definition of double-replacement reaction and gives a number of examples.
Double-Replacement Reaction Definition AC + BD
Example One: Lead Nitrate and Potassium Iodide
When an aqueous solution of lead nitrate is added to an aqueous solution of potassium iodide it forms lead iodide. The precipitate formation occurs when the cations of one reactant combine with the anions of the other reactant to form a totally or partially insoluble compound.
Example Two: Calcium Carbonate and Sulfurous Acid
How is marble eroded by acid rain? Atmospheric sulfur dioxide combines with rainwater to create sulfurous acid. The primary component of marble is calcium carbonate (CaCO3). The sulfurous acid reacts with the CaCO3 in the marble and dissolves it.
Example Three: Sodium Chloride and Silver Nitrate
When an aqueous solution of silver nitrate is combined with an aqueous solution of sodium chloride, silver chloride is formed.
Spectator Ions
Two aqueous solutions of ionic compounds are simply sets of dissolved ions, each possessing both positive and negative ion material. When the two are combined, they form a mixture of four ions. If two of the ions can form an insoluble material, a covalent material or an escaping gas, it can be categorized as a reaction. Not all ions take part in the reaction -- those that do not are called "spectator ions."
Tags: aqueous solution, sulfurous acid, When aqueous, When aqueous solution