question_answer 36)

When metal X is treated with sodium hydroxide; a white precipitate (A) is obtained, which is soluble in excess of \[NaOH\]to give a soluble complex (B). Compound (A) is soluble in \[HCl\](dilute) to form compound (C). The compound (A) when heated strongly gives (D), which is used to extract metal. Identify (X), (A), (B), (C) and (D). Write suitable equations to support their identities.

Answer:

Since, (X) dissolves in \[NaOH\]solution and gives a white precipitate which dissolves in excess of \[NaOH\]form soluble complex. (X) must be aluminium metal and (A) must be aluminium hydroxide, \[Al{{(OH)}_{3}}\]. \[Al{{(OH)}_{3}}\]dissolves in excess of \[NaOH\]form (B) which is sodium tetrahydroxoaluminate White ppt. \[Al+2NaOH+2{{H}_{2}}O\to 2NaAl{{O}_{2}}+3{{H}_{2}}\] \[NaAl{{O}_{2}}+2{{H}_{2}}O\rightleftharpoons \underset{\begin{smallmatrix} (A) \\ White\,ppt. \end{smallmatrix}}{\mathop{Al{{(OH)}_{3}}}}\,+NaOH\] \[Al{{(OH)}_{3}}+NaOH\to \underset{\text{Soluble}\,\text{complex}}{\mathop{Na[Al{{(OH)}_{4}}]}}\,\] (A) dissolves in dilute \[HCl\] to form \[AlC{{l}_{3}}\] (C) \[Al{{(OH)}_{3}}+3HCl\to \underset{(C)}{\mathop{AlC{{l}_{3}}}}\,+3{{H}_{2}}O\] (A) when heated strongly forms \[A{{l}_{2}}{{O}_{3}}\]which is used for the extraction of aluminium metal. \[2Al{{(OH)}_{3}}\xrightarrow{Heat}\underset{(D)}{\mathop{A{{l}_{2}}{{O}_{3}}}}\,+3{{H}_{2}}O\]