| (i) Its aqueous solution is alkaline to litmus. |
| (ii) On strongly heating it swells to give a glassy bead |
| (iii) When concentrated sulphuric acid is added to hot concentrated solution of (x), crystals of \[{{H}_{3}}B{{O}_{3}}\]separate out. Identify the colour of these crystals. |
A) Violet
B) Blue
C) Brown
D) White
Correct Answer: D
Solution :
[d] (X) is borax, \[N{{a}_{2}}{{B}_{4}}{{O}_{7}},10{{H}_{2}}O\] (i) \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}+7{{H}_{2}}O\rightleftharpoons \underset{\begin{matrix} (strong) \\ Base \\ \end{matrix}}{\mathop{2NaOH}}\,+\underset{\begin{matrix} (weak) \\ acid \\ \end{matrix}}{\mathop{4{{H}_{3}}B{{O}_{3}}}}\,\] Due to presence of\[NaOH\], the aqueous solution is alkaline to litmus. (ii) \[N{{a}_{2}}{{B}_{4}}{{O}_{7}},10{{H}_{2}}O\xrightarrow[(swells)]{Heat}N{{a}_{2}}{{B}_{4}}{{O}_{7}}+10{{H}_{2}}O\]\[\to 2NaB{{O}_{2}}+\underset{Glassy\,bead}{\mathop{{{B}_{2}}{{O}_{3}}}}\,\] (iii) \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}+{{H}_{2}}S{{O}_{4}}+5{{H}_{2}}O\to N{{a}_{2}}S{{O}_{4}}+\underset{white\,crystals}{\mathop{4{{H}_{3}}B{{O}_{3}}}}\,\]
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