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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. |
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Answer» (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))`. |
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