Question

A litre of air containing 1 % Ar is repeatedly passed over hot Cu and hot Mg till no reduction of volume takes place. The final volume of Ar shall be:
A.${\text{0mL}}$
B.${\text{230mL}}$
C.${\text{770mL}}$
D.${\text{10mL}}$

Answer 1

Hint: Air is an example of a homogeneous mixture of various substances. It consists of different kinds of gases like nitrogen, oxygen, carbon dioxide, inert or noble gases and various other substances.
-Noble gases have very low or no chemical reactivity towards metals.

Complete step by step answer:
Given that a litre of air containing 1 percent argon gas is repeatedly passed over hot copper and hot magnesium till no reduction of volume takes place.
We need to find out the final volume of the argon gas.
The volume of air according to the question is one litre which is equal to 1000 milliliters.
The volume of argon gas present in air is one percent of the total volume of air.
In other words, the volume of argon present in air $ = \dfrac{1}{{100}} \times 1000 = 10$ milliliters.
Hence, the initial volume of argon present in air before air is passed over hot copper and hot magnesium is 10 milliliters.
Now, when air is passed over hot copper and hot magnesium, argon will not undergo any reaction since it is an inert gas and thus has no chemical reactivity. But other constituents like nitrogen and oxygen are also present in air. These are reactive and so nitrogen will react with hot magnesium to form magnesium nitride and oxygen will react with copper to form copper oxide.
So, if the air is passed over hot copper and hot magnesium till no reduction of volume takes place, then by that time all the nitrogen and oxygen will completely be reacted. As a result, only the argon will be left in the air.
So, the final volume of argon in air will be equal to the initial volume of argon which is 10 milliliters. So, the final volume of argon is also 10 milliliters. Hence, the correct option is D.

Note:
-Argon gas can be used to extinguish fires without damaging server equipment.
-Argon can displace oxygen and moisture and hence it is used to increase the shelf lives of the contents of a packaging material.
-Argon is also used as a preservative for paints and varnish.