question_answer 1)

  When aqueous solution of borax is acidified with hydrochloric acid, a white crystalline solid which is soapy to touch. Is this solid acidic or basic in nature? Explain.

Answer:

  When aqueous solution of borax is acidified with\[HCl\], a crystalline solid which is soapy to touch is formed. This is orthoboric acid. It is a Lewis acid as it combines with \[O{{H}^{-}}\] ion of water to form \[{{[B{{(OH)}_{4}}]}^{-}}\] ion with release of \[{{H}^{+}}\]ion. \[\underset{Borax}{\mathop{N{{a}_{2}}{{B}_{4}}{{O}_{7}}}}\,+2HCl+5{{H}_{2}}O\xrightarrow{{}}\underset{Boric\,acid}{\mathop{4{{H}_{3}}B{{O}_{3}}}}\,+2NaCl\]\[{{H}_{3}}B{{O}_{3}}+{{H}_{2}}O\xrightarrow{{}}{{[B{{(OH)}_{4}}]}^{-}}+{{H}^{+}}\xrightarrow[{}]{{{H}_{2}}O}{{H}_{3}}{{O}^{+}}\]