Question

When copper is dipped in the solution of silver nitrate, the solution turns blue. Give the reason along with the chemical equation.

Answer 1

Now we see the double decomposition reaction.
The reaction in which the two reactants interchange their positive and negative ions and form a new compound is called a double decomposition reaction and also called displacement reaction. The general equation of the reaction is,
$AB + CD\xrightarrow{{}}AD + CB$

Complete step by step answer:

Let us see an example of a double decomposition reaction.
On heating, ferrous sulfate crystals lose water and it forms anhydrous ferrous sulfate so the color of the crystal changes from light green to white, and on further heating anhydrous ferrous sulfate decomposes to give ferric oxide, sulfur dioxide, and sulfur trioxide.

$2FeS{O_4}\xrightarrow{\Delta }F{e_2}{O_3} + S{O_2} + S{O_3}$

In the single reaction ferrous sulfate decomposed into three products thus it is a decomposition reaction.
When copper is dipped in the solution of silver nitrate, the solution turns blue because Copper displaces silver from silver nitrate to form silver metal and cupric nitrate.

$Cu + 2AgN{O_3}{\text{ }} \to Cu{\left( {NO{\text{ }}3{\text{ }}} \right)_2}{\text{ }} + 2Ag$

Additional Information:
Neutralization and precipitation reactions are some more examples of double decomposition reactions.

Neutralization:
Neutralization may be a double decomposition reaction that occurs between the acids and bases. The reaction between vinegar and bicarbonate of soda is an example of neutralization.

Precipitation reaction:
A precipitation reaction may be a double decomposition that occurs between two aqueous ionic compounds which form a replacement insoluble ionic compound. The reaction between lead (II) nitrate and iodide is an example of a precipitation reaction.

Note:
Now we can discuss about the difference between the chemical displacement and decomposition reaction as,
Chemical displacement:
In the chemical reaction if one metal displaces to another compound form a new product called chemical displacement reaction.
Example: $Zn + 2HCl\xrightarrow{{}}ZnC{l_2}{\text{ }} + {H_2}$
Let discuss about the chemical decomposition as,
Chemical decomposition:
The chemical reaction in which reactants decompose into two or more products called chemical decomposition.
Example: $CaC{O_3}\xrightarrow{\Delta }CaO + C{O_2}$.