Question

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

(i) Heating with stream of carbon monoxide.

(ii) Heating with iodine.

(iii) Liquation.

(iv) Distillation.

Answer 1

(i) Heating with stream of carbon monoxide.

(ii) Heating with iodine.

Explanation:

In vapour phase refining method, the metal is converted into its volatile compound and collected elsewhere. It is then decomposed to give pure metal.

Mond process for refining nickel: In this process, nickel is heated in a stream of carbonmonoxide forming a volatile complex, nickel tetracarbonyl.

\[\ce{Ni + 4CO ->[330 - 350K] Ni(CO)4}\]

The carbonyl is subjected to higher temperature so that it is decomposed giving the pure metal:

\[\ce{Ni(CO)4 ->[450 - 470K] Ni + 4CO}\]

The metal iodide being more covalent, volatilises:

\[\ce{Zr + 2I2 -> ZrI4}\]

The metal iodide is decomposed on a tungsten filament, electrically heated to about 1800 K.

The pure metal is thus deposited on the filament.

\[\ce{ZrI4 -> Zr + 2I2}\]