Question

Explain what happens when boric acid is heated.

Answer 1

Hint: The molecular formula of boric acid is ${{H}_{3}}B{{O}_{3}}$. Boric acid is prepared from borax ($N{{a}_{2}}{{B}_{4}}{{O}_{7}}$). When boric acid is heated at different temperatures it loses water in three different stages and forms various products.

Complete step-by-step answer:
There are three stages in heating of boric acid.

Stage-1:
When boric acid (${{H}_{3}}B{{O}_{3}}$) is heated at 370 K it forms metaboric acid and water.

& \underset{\text{Boric acid }}{\mathop {{H}_{3}}B{{O}_{3}}}\,\text{ }\xrightarrow{370K}\text{ }\underset{\text{Metaboric acid}}{\mathop HB{{O}_{2}}}\,\text{ }+\underset{Water}{\mathop {{H}_{2}}O}\, \\\ & \text{ } \\\ \end{aligned}$$ Stage-2: The product formed in stage-1 (metaboric acid) is converted into Tetraboric acid at 410 K by losing water. $$\underset{\text{Metaboric acid}}{\mathop 4HB{{O}_{2}}}\,\text{ }\xrightarrow{410K}\underset{\text{Tetraboric acid}}{\mathop {{H}_{2}}{{B}_{4}}{{O}_{7}}}\,+\underset{Water}{\mathop {{H}_{2}}O}\,$$ Stage-3: Tetraboric acid at red heat temperature forms boron trioxide or borax by losing water. $$\underset{\text{Tetraboric acid}}{\mathop {{H}_{2}}{{B}_{4}}{{O}_{7}}}\,\xrightarrow{\operatorname{Re}d\text{ }heat}\underset{\text{Boron trioxide}}{\mathop 2{{B}_{2}}{{O}_{3}}}\,+\underset{Water}{\mathop {{H}_{2}}O}\,$$ Additional information: Borax is also called sodium tetraborate and it is a powdery white mineral. Borax has countless uses in the modern world. We can use borax both at house and in industry. In house we can use borax to kill insects such as ants. Borax is used as washing detergents to help whiten and get rid of dirt from clothes. Borax can neutralize aromas and softens hard water. In industry borax can be used as a buffer, a dispersion agent, and welding flux and to regulate viscosity. Note: To get borax we have to heat tetra boric acid at red heat. Borax won’t be formed as a first product by direct heating of boric acid. Borax has so many applications including home and industrial applications.