| A certain salt (X) gives the following tests: |
| (I) Its aqueous solution is alkaline to litmus. |
| (II) On strongly heating it swells to give a glassy bead. |
| When concentrated sulphuric acid is added to a hot concentrated solution of (X), crystals of \[{{H}_{3}}B{{O}_{3}}\]separate out. |
| Identify the colour of these crystals. |
A) White
B) Blue
C) Brown
D) Violet
Correct Answer: A
Solution :
| (i) \[N{{a}_{2}}\underset{(X)}{\mathop{{{B}_{4}}}}\,{{O}_{7}}+7{{H}_{2}}O2\underset{\begin{smallmatrix} \left( strong \right) \\ \,\,\,base \end{smallmatrix}}{\mathop{NaO}}\,H+4\underset{\begin{smallmatrix} \left( week \right) \\ \,\,\,acid \end{smallmatrix}}{\mathop{{{H}_{3}}B}}\,{{O}_{3}}\] |
| Due to presence of \[NaOH\], the aqueous solution is alkaline to litmus. |
| (ii) \[N{{a}_{2}}\underset{(X)}{\mathop{B}}\,{{O}_{7}}.10{{H}_{2}}O\xrightarrow[(swells)]{Heat}N{{a}_{2}}{{B}_{4}}{{O}_{7}}\] |
| \[+10{{H}_{2}}O\xrightarrow{{}}2NaB{{O}_{2}}+\underset{Glassy\,bead}{\mathop{{{B}_{2}}{{O}_{3}}}}\,\] |
| From the above two test it is confirmed that salt (X) is Borax, \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}.10{{H}_{2}}O.\] |
| \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}+{{H}_{2}}S{{O}_{4}}+5{{H}_{2}}O\xrightarrow{{}}\]\[N{{a}_{2}}S{{O}_{4}}+4\underset{white\,crystals}{\mathop{{{H}_{3}}B{{O}_{3}}}}\,\] |
You need to login to perform this action.
You will be redirected in
3 sec
