Boric Acid Crystals: Properties, Formation & Uses

Boron forms several oxyacids (acid that contains oxygen), collectively called boric acid, that crystallize in white, lustrous flakes known as boric acid crystals.

Preparation

• Boric acid crystals are obtained in large quantities from borax (a boron-containing mineral). A hot concentrated solution of the mineral is treated with calculated amounts of sulfuric acid; the liquid, when cooled, contains crystals of boric acid.

Physical Properties

• Boric acid crystals are slightly soluble in cold water and moderately soluble in hot water. Volatile in steam, they add a green coloration to an uncolored flame.

Chemical Properties

• Boric acid crystals, when heated to 100 C, lose a water molecule, creating metaboric acid; this compound, after being heated to 160 C, forms tetraboric acid.

Layer Structure

• Boric acid crystals consist of a number of layers which are linked together. It is due to this "layer structure" that boric acid crystals, when in a solid state, consist of flakes which are slippery to the touch.

Uses

• Boric acid crystals are used in the manufacture of enamels and glazes for pottery, as well as in borax phenolphthalein tests.