When an aqueous solution of borax is acidified with hydrochloric acid, a white crystalline solid is formed which is soapy to touch. Is this solid acidic or basic in nature? Explain.
Orthoboric acid is formed when the aqueous solution is acidified with borax. Orthoboric acid is crystalline and soapy to touch. It is soluble in hot water.
Na2B4O7 + 2HCl + 5H2O → 2NaCl + 4B(OH)3
Boric acid is a weak monobasic acid. It acts a lewis acid by taking electrons from the hydroxyl group.
B(OH)3 + 2H2O → [B[OH]4]- + H3O+
Heating orthoboric acid at 370K gives metaboric acid and on further heating give Boric acid
H3BO3 → HBO2 → B2O3