+ Na SO Ca B O + 11H O + 4SO 2Ca(HSO ) + 6H BO Properties: Boric acid is a colourless transparent crystal. It is a very weak monobasic acid and, it accepts hydroxyl ion rather than donating proton. B(OH) + 2H O H O + + [B(OH) ] - It reacts with sodium hydroxide to form sodium metaborate and sodium tetraborate. H BO + NaOH NaBO + 2H O 4H BO + 2NaOH Na B O + 7H O Action of Heat: Boric acid when heated at K gives metaboric acid and at K, it gives tetraboric acid.
When heated at red hot, it gives boric anhydride which is a glassy mass. - - - - 4H BO 4HBO + H O K 4HBO H B O + H O K H B O 2B O + H O Red hot Acton of ammonia Fusion of urea with B(OH) , in an atmosphere of ammonia at - K gives boron nitride. B(OH) + NH Δ BN + 3H O Ethyl Borate test When boric acid or borate salt is heated with ethyl alcohol in presence of conc. sulphuric acid, an ester, triethylborate is formed.
The vapour of this ester burns with a green edged flame and this reaction is used to identify the presence of borate. H BO + 3C H OH B(OC H ) + 3H O Conc. H SO Note: The trialkyl borate on reaction with sodium hydride in tetrahydrofuran to form a coordination compound Na[BH(OR) ], which acts as a powerful reducing agent. Formation of boron trifluoride: Boric acid reacts with calcium fluoride in presence of conc.
sulphuric acid and gives boron trifluoride. 3CaF + 3H