Chemistry PREPARATION, PROPERTIES, USES & STRUCTURE OF ALUMINIUM CHLORIDE, ALUMS ETC.

`Al_2O_3` (Corundom) :

Preparation :

(i) `2Al(OH)_3 overset(300^oC) rightarrow Al_2O_3 + 3H_2O`

(ii) `Al_2(SO_4)_3 overset(Delta) rightarrow Al_2O_3 + 3SO_3`

(iii) `(NH_4)_2SO_4*Al_2(SO_4)_3*24H_2O overset(Delta) rightarrow Al_2O_3 + 2NH_3 + 4SO_3 + 25H_2O`

Properties :

(i) It is very stable and unreactive.

(ii) Melting point `rightarrow 2050^oC`

Boiling point `rightarrow 2980^oC`

(iii) It is amphoteric oxide :

`Al_2O_3 + 6HCl rightarrow 2AlCl_3 + 3H_2O`

`Al_2O_3 + NaOH rightarrow 2NaAlO_2 + H_2O`

(iv) Reaction with carbon :

`2Al_2O_3 + 9C overset (2000^oC) rightarrow Al_4C_3 + 6CO`

`Al_4C_3 overset(12H_2O) -> 4Al(OH)_3 + 3CH_4`

Uses :

(i) It is used as a refractory material.

(ii) In chromatography for separation of mixture.

(iii) In preparation of Artificial gems.

`AlCl_3`

Preparation :

(i) `undersettext((over heated))(2Al) + undersettext(dry)(6HCl) text(vap.) rightarrow 2AlCl_3 + 3H_2`

(ii) `Al_2O_3 + 3C + 3Cl_2underset(1000^oC)overset(Delta) rightarrow (2AlCl_3)text(vap.) + 3CO`

`(2AlCl_3)text(vap.) undersettext(cooled) -> text(solid anh.) AlCl_3`

Properties :

(i) Its anhydrous forme is deliquescent and fumes in air.

(ii) It sublimes at `180^oC`.

(iii) It is covalent and exists in the form of dimer even if in non polar solvents e.g. alc., ether, benzene, where it is soluble in fair extent.

Uses :

(i) Friedel-Craft reaction.

(ii) Dyeing, drug & perfumes etc.

Alums :

`M_2SO_4*M'_2(SO_4)_3*24H_2O`

Properties :

Swelling characteristics

where `M = Na^+`, `K^+`, `Rb^+`, `Cs^+`, `As^+`, `Tl^+`, `NH^+`

`M' = Al^(+3)`, `Cr^(+3)`, `Fe^(+3)`, `Mn^(+3)`, `Co^(+3)`

`K_2SO_4*Al_2(SO_4)_3*24H_2O` Potash alum

`(NH_4)_2SO_4*Al_2(SO_4)_3*24 H_2O` Ammonium alum

`K_2SO_4*Cr_2(SO_4)_3*24H_2O` Chrome alum

`(NH_4)_2SO_4* Fe_2(SO_4)_3*24H_2O` Ferric alum

Preparation :

`Al_2O_3 + 3H_2SO_4 rightarrow Al_2(SO_4)_3 + 3H_2O`

`Al_2(SO_4)_3 + K_2SO_4 + text(aq. soln) rightarrow text(crystallise)`

Uses :

(i) Act as coagulant.

(ii) Purification of water.

(iii) Tanning of leather.

(iv) Mordant in dying.

(v) Antiseptic.