Question
Explain what happens when boric acid is heated.
✓
Answer
On heating orthoboric acid $\left(\mathrm{H}_3 \mathrm{BO}_3\right)$ at 370 K or above, it changes to metaboric acid $\left(\mathrm{HBO}_2\right)$. On further heating, this yields boric oxide $\mathrm{B}_2 \mathrm{O}_3$.
$\text{H}_3\text{BO}_3 \ \ \ \ \ \xrightarrow[370\text{k}]{\Delta}\ \ \ \ \ \ \text{HBO}_2 \ \ \ \ \ \ \xrightarrow[\text{red hot}]{\Delta} \ \ \ \ \ \ \text{B}_2\text{O}_3 \\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Metaboric acid} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Boric oxide}$
$\text{H}_3\text{BO}_3 \ \ \ \ \ \xrightarrow[370\text{k}]{\Delta}\ \ \ \ \ \ \text{HBO}_2 \ \ \ \ \ \ \xrightarrow[\text{red hot}]{\Delta} \ \ \ \ \ \ \text{B}_2\text{O}_3 \\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Metaboric acid} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Boric oxide}$
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