1.

(a) Describe the preparation of potassium dichromate.

Answer»

Solution :Potassiumdichromate ispreparedfromchromate ore.Theore isconcentrated by gravityseparation . It ismixedwithexcesssodiumcarbonateandlimeandroastedin areverbratoryfurnace .
`4FeCr_(2) O_(4) + 8Na_(2) CO_(3)+ 7O_(2) overset(900 - 100^(@)C(to)`
Theroasted massis treated withwaterto separatesolublesodiumchromatefrominsolubleironoxide. They yellossolution of sodium chromate istreatedwith conc. sulphuricacid whichconvertssodiumchromateintosodiumdichromate .
`2Na_(2) CrO_(4) + H_(2) SO_(4) toNa_(2) Cr_(2) O_(3) + Na_(2) SO_(4) + H_(2) O`
Theabovesolutionis concentrated to removelesssolublesodium sulphate . theresultingsolutionis filteredand furtherconcentrated . It iscooledto getthecrystalsof `Na_(2) SO_(4) 2H_(2)O`.
Thesaturatedsolutionof sodiumdichromate in water in mixedwith KCIand thencon.centreatedto getcrystalof NaCI. It is filteredwhilehot andfilratecooledto OBTAIN`K_(2) Cr_(2) O_(7)` crystals.


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