Tetraboric acid
# Tetraboric acid

Tetraboric acid or pyroboric acid is a chemical compound with empirical formula $H_2B_4O_7.$ It is a colourless water-soluble solid formed by the dehydration or polymerization of boric acid.

Tetraboric acid is formally the parent acid of the tetraborate anion $[B_4O_7]^{2−}.$

## Preparation

Tetraboric acid can be obtained by heating orthoboric acid $B(OH)_3$ above about 170 °C:

    4 $B(OH)_3$ → $H_2B_4O_7$ + 5 $H_2O$
