Question

In the following reactions:

& {{H}_{3}}B{{O}_{3}}\xrightarrow{375K}A\xrightarrow{redheat}{{B}_{2}}{{O}_{3}} \\\ & {{H}_{3}}B{{O}_{3}}\xrightarrow{435K}B\xrightarrow{redheat}{{B}_{2}}{{O}_{3}} \\\ \end{aligned}$$ The compounds A and B are:

Answer 1

Boric acid also known as hydrogen borate, boracic acid, orthoboric acid etc has the chemical formula ${{H}_{3}}B{{O}_{4}}$ . boric acid is prepared using borax and when boric acid is heated at different temperature, this results in loss of water in three different stages to form various product.

Complete Solution :
The three stages in which the boric acid is heated is mentioned below:
Stage 1:
When we heat boric acid at 370K it forms metaboric acid and water and if it is further treated at red heat temperature it produces boron trioxide. The reaction involved is mentioned below:
${{H}_{3}}B{{O}_{3}}\xrightarrow{375K}HB{{O}_{2}}+{{H}_{2}}O\xrightarrow{redheat}{{B}_{2}}{{O}_{3}}$
Stage 2:
When we heat boric acid at 435K it forms tetra boric acid and water and if it is further treated at red heat temperature it produces boron trioxide. The reaction involved is mentioned below:
${{H}_{3}}B{{O}_{3}}\xrightarrow{435K}{{H}_{2}}{{B}_{4}}{{O}_{7}}+{{H}_{2}}O\xrightarrow{redheat}{{B}_{2}}{{O}_{3}}$
stage 3:
Tetra boric acid at red heat temperature forms boron trioxide or borax by losing water.
${{H}_{2}}{{B}_{4}}{{O}_{7}}\to 2{{B}_{2}}{{O}_{3}}+{{H}_{2}}O$

Additional information:
Borax is also known as sodium tetraborate and it is a powdery mineral which is white in colour. Borax has countless uses in the modern world; it is generally used in both houses and industries. In house it is generally used to kill insects and in industries it is used in the form of detergents to remove dirt from clothes.

Note: To obtain borax we need to head tetra boric acid at red heat. Borax would not be the first product formed when tetra boric acid is heated. Boric acid exists in polymeric form due to the presence of intermolecular hydrogen bonding.