4)What is the process involved inthe Dewar method of separation of inert gases?

Procedure: Separation of noble gases is carried out in a flask designed by Dewar called as Dewar's flask. It is a double walled flask containing activated coconut charcoal in the middle. A tube is arranged above the flask, to introduce the gaseous mixture and to remove the unadsorbed gases. The procedure involves the following steps.

Step i: The mixture of noble gases is brought in contact with charcoal (Charcoal -1)kept in a Dewar's flask maintained at a temperature of 173K.It is allowed to remain for one hour, when argon, krypton and xenon gases get adsorbed while helium and neon remain unadsorbed and are pumped out of the bulb.

Step ii: The mixture of helium and neon is introduced into another bulb containing coconut charcoal (Charcoal - 2) maintained at a temperature of 93K.Only neon gets adsorbed leaving behind helium which is pumped out. This charcoal is warmed to recover neon.

Step iii: The first charcoul with Argon, Krypton and Xenon adsorbed on it is brought in contact with another charcoal (Charcoal - 3) cooled to liquid air temperature (11K). Argon being a lighter gas diffuses into this charcoal (at 77K)and is recovered by warming separately.

Step iv: Krypton and Xenon which are still on the first charcoal (Charcoal -1)are separated by raising the temperature of the charcoal to 183X". At this temperature krypton cannot remain in the adsorbed state and it is collected. Xenon which remains on the first charcoal is released by warming and is collected separately. All these changes are shown schematically.

Thank You

Ruchi

Askiitians Faculty