JEE Main 2021 · 25 February · evening · Single correct · +4 / −1
The method used for the purification of Indium is :
- (a) zone refining
- (b) vapour phase refining
- (c) liquation
- (d) van Arkel method
Answer and solution
Answer (a) zone refining
Solution
Chemistry ma’am · 3 steps
Indium is needed ultrapure for semiconductors, and that level of purity comes from zone refining.
- Zone refining idea. A narrow molten zone is moved slowly along a rod of impure metal. Impurities are more soluble in the melt than in the solid, so they travel with the molten zone to one end. That end is then cut off.
- Why indium. Indium, like Si, Ge, B and Ga, is used in semiconductors and must be extremely pure. Zone refining is the method that reaches this very high purity.
Method How it works Typical metals Zone refining impurities move along with a moving molten zone Si, Ge, B, Ga, In Vapour phase refining metal forms a volatile compound, which then decomposes to pure metal Ni (Mond process), Zr, Ti Liquation low-melting metal melts and flows away from infusible impurities Sn, Pb, Bi van Arkel method volatile iodide decomposed on a hot filament Zr, Ti - So. Indium is purified by zone refining, option (a).
The idea to keep. Need extremely high purity, as for semiconductors? Think zone refining: Si, Ge, B, Ga, In. Volatile compound route means Mond (Ni) or van Arkel (Zr, Ti). Low-melting metal draining off impurities means liquation.
Answer from the NTA final answer key. Solution by PrepWiser.