Question

Coconut charcoal at $-100{}^\circ C$ adsorbs a mixture of:
(A) He and Kr
(B) Ar, Kr, and Xe
(C) Kr and Xe
(D) He and Ne

Answer 1

Hint: The coconut charcoal is used to separate the noble gases in the Dewar’s process. So, studying Dewar’s process in brief can help us reach the required answer.

Complete Solution :
Let us study the Dewar’s process to solve the given problem;
Dewar’s process-
- The method of separation of noble gases by using the coconut charcoal at distinct temperatures is known as Dewar’s method. The process can be briefly described as,
- The Dewar charcoal adsorption method is the method where noble gases such as He, Ar, Ne, Xe and Kr are separated from their mixture at different temperatures by using coconut charcoal.
- The coconut charcoal adsorbs different gases at different temperatures. The process takes place in Dewar’s flask as shown in the figure.
- The coconut charcoal is placed in a low temperature bath at 173 K where Ar, Kr and Xe are adsorbed. -Then the temperature is lowered till 93 K and Ne is absorbed leaving He as free gas from the process.
- Further separation of these gases takes place by fractional distillation or by repeated charcoal adsorption.
So, we can see that coconut charcoal at $-100{}^\circ C$ (173 K) adsorbs a mixture of Ar, Kr and Xe.
So, the correct answer is “Option B”.

Note: Do note that at any temperature in Dewar’s flask experiment, He is never adsorbed on the coconut charcoal. So, the options containing He in them can be ignored from start i.e. option (A) and (D).