Verified Answer :
\(H_{3}BO_{3} and H_{3}PO_{4}\) are weak electrolytes. They partially ionize in solutions as below,
\(H_{3}BO_{3} (aq)<==>3H^{+}(aq)+BO_{3}^{3-}(aq)\)
\(H_{3}PO_{4} (aq)<==>3H^{+}(aq)+PO_{4}^{3-}(aq)\)
The number of ions increase in solution apparently but this increase will be very less as these compounds are weak electrolytes, there will be a little increase in conductivity of these compounds in solutions. Unlike strong electrolytes these compounds show a very little increase in the concentration of ions although there is a subscript of 3 on hydrogen as these compounds partially ionize in solution.
The additional ions found in the solutions are,
\({{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}\),\({{\text{H}}_{\text{2}}}{\text{PO}}_4^ -\),\({\text{HPO}}_4^{2-}\),\({\text{PO}}_4^{3 - }\) in case of \({{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}\) and \({{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_3}\),\({{\text{H}}_{\text{2}}}{\text{BO}}_3^ -\),\({\text{HBO}}_3^{2 - }\),\({\text{BO}}_3^{3 - }\) in case of \({{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_3}\).
Further explanation:
Weak electrolyte:
The electrolyte which does not dissociate completely in the aqueous solution is known as weak electrolyte. Weak electrolyte only ionizes from 1 % to 10 %. For example, HF (hydrofluoric acid) and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) (acetic acid), \({{\text{H}}_2}{\text{O}}\) (water), \({\text{N}}{{\text{H}}_3}\)(ammonia).
Strong electrolyte:
The electrolyte which dissociates completely in the aqueous solution is known as strong electrolyte. Strong electrolyte 100 % ionizes in the water. For example, HCl (hydrochloric acid), NaCl (sodium chloride), HBr (hydrobromic acid), HI (hydroiodic acid).
The given compounds \({{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_3}\) and \({{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}\) are weak electrolytes thus they do not ionize in water completely. Therefore \({{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_3}\) and \({{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}\) dissociates partially in water.
The dissociation reaction of \({{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}\) is as follows:
\({{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{4}}}+{{\text{H}}_{\text{2}}}{\text{O}} \rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}+{{\text{H}}_{\text{2}}}{\text{PO}}_4^-\\ {{\text{H}}_{\text{2}}}{\text{PO}}_4^-+{{\text{H}}_{\text{2}}}{\text{O}} \rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}+{\text{HPO}}_4^{2 - }\\{\text{HPO}}_4^-+ {{\text{H}}_{\text{2}}}{\text{O}}\rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}+{\text{PO}}_4^{3 - }\)
The dissociation reaction of \({{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_3}\) is as follow
\({{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_{\text{3}}}+{{\text{H}}_{\text{2}}}{\text{O}} \rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}+{{\text{H}}_{\text{2}}}{\text{BO}}_3^-\\ {{\text{H}}_{\text{2}}}{\text{BO}}_3^-+{{\text{H}}_{\text{2}}}{\text{O}} \rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}+{\text{HBO}}_3^{2 - }\\{\text{HBO}}_3^-+ {{\text{H}}_{\text{2}}}{\text{O}}\rightleftharpoons {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}+{\text{BO}}_3^{3 - }\)
Therefore, the species after partial dissociation can found in the aqueous solution are,
\({{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}\),\({{\text{H}}_{\text{2}}}{\text{PO}}_4^ -\),\({\text{HPO}}_4^{2-}\),\({\text{PO}}_4^{3 - }\) in case of \({{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}\) and \({{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_3}\),\({{\text{H}}_{\text{2}}}{\text{BO}}_3^ -\),\({\text{HBO}}_3^{2 - }\),\({\text{BO}}_3^{3 - }\) in case of \({{\text{H}}_{\text{3}}}{\text{B}}{{\text{O}}_3}\).
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Answer details:
Grade: Senior School
Subject: Chemistry
Chapter: Strong and weak electrolytes
Keywords: H3PO4, H2PO4-, HPO42-, PO43-, weak electrolyte, strong electrolyte, H3BO3, H2BO3-, HBO32-, BO33-, boric acid, dissociation, completely dissociate, partial dissociate, aqueous solution, electrochemistry,