question_answer 28)

Explain what happens when : (a) Borax is heated strongly? (b) Boric acid is added to water? (c) Aluminium is treated with\[NaOH\]? (d)\[B{{F}_{3}}\] is reacted with ammonia ?  

Answer:

(a) When borax is heated strongly, it first becomes anhydrous and then breaks up into sodium metaborate and boric anhydride (a transparent glassy bead). (b) Boric acid acts as a weak acid by accepting hydroxyl ion from water and releasing a proton. \[B{{(OH)}_{3}}+{{H}_{2}}O\to {{[B{{(OH)}_{4}}]}^{-}}+{{H}^{+}}\] (c) Hydrogen is released. \[2Al+2NaOH+6{{H}_{2}}O\to 2Na[Al{{(OH)}_{4}}]+3{{H}_{2}}\](d) An addition complex is formed as NH3 acts as a Lewis base and BF3 as a Lewis acid. \[\underset{\begin{smallmatrix} Lewis \\ Acid \end{smallmatrix}}{\mathop{B{{F}_{3}}}}\,+\underset{\begin{smallmatrix} Lewis \\ Base \end{smallmatrix}}{\mathop{N{{H}_{3}}}}\,\to {{F}_{3}}B\leftarrow N{{H}_{3}}\]