When metal X is treated with sodium hydroxide, a white precipitate (A) is obtained, which is soluble in excess of NaOH to give soluble complex (B). Compound (A) is soluble in dilute HCl 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.

Explanation

Since metal X reacts with `NaOH` to first give a white ppt. (A) which dissolves in excess of NaOH to give a soluble complex (B), therefore , metal (X) must be Al , ppt (A) must be `Al(OH)_(3)` and complex (B) must be sodium tetrahydroxoaluminate (III).
`{:(underset((X))(2Al) + 3NaOH rarr underset(" Aluminium hydroxide (ppt.) ")(Al(OH)_(3)darr) + 3Na^(+)),(underset((A))(Al(OH)_(3))+NaOHrarr underset("Sod. tetrahydroxoaluminate (III)")underset((B))(Na^(+)[Al(OH)_(4)]^(-))):}`
Since (A), i.e, `Al(OH)_(3)` react with dil. `HCl` to give compound (C), therefore, (C ) must be `AlCl_(3)`.
`underset((A))(Al(OH)_(3)) + 3HCl rarr underset((C ))(AlCl_(3)) + 3H_(2)O`
Since (A) on heating gives (D) which is used to extract metal (i.e, electrolysis of `Al_(2)O_(3)` gives Al metal),
therefore , (D) must be alumina `(Al_(2)O_(3))`
`underset((A))(2Al (OH)_(3)) overset(Delta)rarr underset((D)) (Al_(2)O_(3)) + 3H_(2)O`