Question

In which of the following methods of purification, metal is converted to its volatile compound which is decomposed to give pure metal?

• A. heating with iodine.
• B. heating with a stream of carbon monoxide.
• C. liquation.
• D. distillation

Answer 1

Answer: (A), (B)

heating with a stream of carbon monoxide.

Correct Answer- Option A and B

Part 1: Mond’s process

In Mond’s process impure Ni is heated in a stream of carbon monoxide and it forms a Nickel tetracarbonyl complex which is volatile and on decomposition gives the pure metal.

$Ni+4CO\to Ni(CO{)}_4$

$NiC{O}_4\to Ni\left(pure\right)+4CO\left(at460K\right)$

Part 2: Van Arkel process

In Van Arkel process Impure Zr or Ti is heated with Iodine in an evacuated vessel and it forms a volatile complex which on decomposition gives the pure metal.

$Zr+2I_2\to Zr{I}_4$

$Zr{I}_4\to Zr\left(pure\right)+2I_2\left(at1800K\right)$

Analysing the options:

Option (A):

In Mond’s process impure Ni is heated in a stream of carbon monoxide and it forms a Nickel tetracarbonyl complex which is volatile and on decomposition gives the pure metal.

Option (B):

In Van Arkel process Impure Zr or Ti is heated with Iodine in an evacuated vessel and it forms a volatile complex which on decomposition gives the pure metal.

Option (C):

In the liquation process a low melting metal like tin can be made to flow on a sloping surface. In this way it is separated from higher melting impurities.

Option (D):

The impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The more basic metal remains in the solution and the less basic ones go to the anode mud.

Hence, the correct options are (A) and (B).