In which of the following method of purification, metal is converted to its volatile compound which is decomposed to give pure metal?
This technique is called vapour phase refining. Mond’s process and Van Arkel process use vapour phase refining.
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 →Ni(CO)4
Ni(CO)4→ Ni(pure) + 4CO (at 460K)
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 + 2I2→ ZrI4
ZrI4→Zr(pure) + 2I2 (at 1800K)