11th Class Chemistry The p-Block Elements-I

  • question_answer 38) A certain salt (X) gives the following results: (i) Its solution is alkaline to litmus. (ii) It swells upto glassy material \[(Y)\] on strong heating. (iii) When concentrated \[{{H}_{2}}S{{O}_{4}}\] is added to hot solution of (X), a white crystal of an acid (Z) separates out. Write equations for all the above reactions and identify (X), (Y) and (Z).


    The salt (X) dissolves and its aqueous solution is alkaline to litmus, it must be a salt of a strong base and a weak acid. On heating it forms a glassy material, hence (X) is a borax. \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}+7{{H}_{2}}O\xrightarrow{{}}\underset{Strong\,alkali}{\mathop{2NaOH}}\,+4{{H}_{3}}B{{O}_{3}}\] \[\underset{(X)}{\mathop{N{{a}_{2}}{{B}_{4}}{{O}_{7}}}}\,\cdot 10{{H}_{2}}O\xrightarrow{Heat}N{{a}_{2}}{{B}_{4}}{{O}_{7}}+10{{H}_{2}}O\] \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}\xrightarrow{Heat}2NaB{{O}_{2}}+{{B}_{2}}{{O}_{3}}\] \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{{}}\underbrace{N{{a}_{2}}S{{O}_{4}}+{{H}_{2}}{{B}_{4}}{{O}_{7}}}_{\underset{(Y)}{\mathop{Glass\,material}}\,}\] \[{{H}_{2}}{{B}_{4}}{{O}_{7}}+5{{H}_{2}}O\xrightarrow{{}}\underset{\underset{\begin{smallmatrix} Orthoboric\,acid \\ (White\,crystals) \end{smallmatrix}}{\mathop{(Z)}}\,}{\mathop{4{{H}_{3}}N{{O}_{3}}}}\,\]  

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