Question

What happens when :
(a) Borax is heated strongly.
(b) Water is added to aluminium nitride.
( c) Dry chlorine gas is added over not mixture of aluminium and coke.
(d) Water is added to aluminium carbide.
( e) Alum is heated.
(f) Aluminium is added to copper sulphate solution .
(g) Aluminium reacts with `HNO_(3)`.
(h) Excess of Excess of caustic soda is added to a solution aluminium chloride.
(i) Aluminium is heated with caustic soda solution.
(j) A mixture of borax and cobalt oxide is heated.

Answer 1

(a) `underset("Borax")(Na_(2)B_(4) O_(7)).10 H_(2) O overset(Delta)rarr Na_(2) B_(4) O_(7) + 10 H_(2) O`
`Na_(2) B_(4) O_(7) overset(Delta) rarr underset("Boric anhydride") (B_(2) O_(3)) + underset ("Sodium metaborate") (2NaBO_(2))`
(b) `underset("Aliminium nitrate") (AlN) + 3H_(2) O rarr underset("Alminium hydroxide") (B_(2) (OH)_(3)) darr + underset("Ammonia") (NH_(3)) uarr`
( c) `Al_(2)O_(3) + 3C + underset("Dry")(3 Cl_(2)) rarr underset("Aluminium chloride") (2AlCl_(3)) + underset("Carbon monoxide") (3CO)`
(d) `underset("Aluminium carbide") (Al_(4) C_(3)) + 12H_(2) O rarr underset("Aluminium hydroxide") (4 Al(OH)_(3)) darr + underset("Methane") (3CH_(4)) uarr`
(e) `K_(2) SO_(4). Al_(2) (SO_(4))_(3). 24H_(2) O overset(200^@ C)rarr K_(2) SO_(4) Al_(2) (SO_(4))_(3) + 24 H_(2) O`
`K_(2) SO_(4).Al_(2) (SO_(4))_(3) overset("Red heat")rarr underset("Burnt alum")underbrace(K_(2) SO_(4) +Al_(2) O_(3)) + 3SO_(3) uarr`.
Alum metls and loses water of crystallisation up to `200^@ C` and a white porus mass is obtained on red heat. This white mass is known as burnt alum.
(f) Aluminium being more electropositive than copper, displaces copper from copper sulphite solution.
`2Al_((s)) + 3 CuSO_(4(aq)) rarr Al_(2) (SO_(4))_(3(aq)) + 3Cu_((s))`
(g) `HNO_(3)` whether concentrated or dilute hardly affects `Al` as aluminium is rendered passive due to formation of thin layer of `Al_(2) O_(3)` on the surface of the metal.
(h) `AlCl_(3) + 3NaOH rarr Al(OH)_(3) + 3NaCl`
(i) `2Al + 2NaOH + 2H_(2) O rarr underset ("Sodium metaluminate") (2NaAlO_(2)) + 2H_(2) uarr`
(j) `Na_(2) B_(4) O_(7). 10 H_(2) O overset(Delta) rarr Na_(2) B_(4) O_(7) + 10 H_(2)O`
`Na_(2) B_(4) O_(7) overset("Red heat") rarr NaBO_(2) + B_(2) O_(3)`
`CoO + B_(2) O_(3) rarr underset("Cobalt metaborate")(Co(CO_(2))_(2))`.