Class 11 chemistry Notes

CLASS 11 CHEMISTRY NOTES: Chemicalproperties of boron

            It exists in five forms, four  of which are crystalline and one is amorphous. All crystalline forms are very hard made up of clusters of B12 units. All crystalline forms are black in appearance and chemically inert. However, it is attacked at high temperature by strong oxidising agents such as a mixture of hot concentrated H2SO4 and HNO3 or Na2O2. But amorphous form is brown and chemically active.

      (a)Reaction with air

            4B + 3O₂   2B₂O₃

            2B + N₂ 2BN

            The above reaction accompanies red  flame. 

            BN + 3H₂O  H₃BO₃  + NH₃

      (b) Action of alkali and acid

            2B + 2NaOH + 2H₂O  ¾®2NaBO₂  + 3H₂

            2B + 3H₂SO₄ 2H₃BO₃ + 3SO₂

            2B + 6HNO₃ 2H₃BO₃ + 6NO₂

      (c)  Reaction with Mg,Ca and consequent hydrolysis

            3Mg + 2B ¾® Mg₃B₂

            3Ca + 2B ¾® Ca₃B₂

            Mg₃B₂ + 6HCl ¾® 3MgCl₂ + B₂H₆

            B₂H₆ + 6H₂O  ¾® 2H₃BO₃ + 6H₂

      (d) Boron reduces SiO₂, CO₂

            3SiO₂ + 4B ¾® 2B₂O₃ + 3Si

            3CO₂ + 4B ¾® 2B₂O₃ + 3C

(e)It decomposes steam, liberating hydrogen gas.