Question

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A lanthanoid metal oxide, LazO3 is reduced to metal by passing 8 amperes of current for 16 h. Mass of lanthanum produced is (At wt. of La = 139)
2.0 kg
20.25 g
451.2 g
221.28​

Answer 1

27.65

Explanation:

since the metal oxide given is La2O3 the valency of metal is 3+

therefore 3Faraday charge is required to deposit 1 mole of the metal(i.e 139g)

(i.e 3×96500C of charge)

since Q=It

so 16×60×60(convert hours into sec)×8 Cof charge will deposit La=16×60×60×139/3*96500

=27.65g of La will be deposited