Question

Which of the following would lose weight on exposure to air?
A. Conc. \[{{H}_{2}}S{{O}_{4}}\]
B. Conc. \[HN{{O}_{3}}\]
C. Anhydrous \[N{{a}_{2}}C{{O}_{3}}\]
D. A saturated solution of \[C{{O}_{2}}\]

Answer 1

Hint: A compound loses weight in air when it does not form a new heavy product after reacting with the air present in the atmosphere, in other words, compound which does not absorb anything from the atmosphere but is itself consumed in the reaction with air present in the atmosphere and loses its weight. If any compound absorbs matter present in the air thus, it becomes heavy and becomes dense.

Complete Step by Step Answer:
If we talk about concentrated \[{{H}_{2}}S{{O}_{4}}\]which is a hygroscopic compound as its name suggests conc. \[{{H}_{2}}S{{O}_{4}}\]absorbs moisture or vapours from the air and gets heavy, dilutes, and results in an increase in volume. This is the reason why conc. hydrochloric acid is placed in air tight bottles to prevent it from reacting with moist air and getting diluted.

Concentrated nitric acid , \[HN{{O}_{3}}\] is a very reactive acid as in this compound oxidation state of nitrogen is +5 which makes it unstable. When it is exposed to air it reacts with oxygen and light to give nitrogen dioxide, water, and also oxygen. HNO3 gets reduced when exposed to air as it forms nitrogen dioxide whose oxidation state is +4. As the oxidation state decreases from converting nitric acid to nitrogen dioxide, nitric acid is absorbed or gains electrons and gets reduced to give nitrogen dioxide.

Anhydrous sodium carbonate, \[N{{a}_{2}}C{{O}_{3}}\] is also known as washing soda without water molecules. It is formed when hydrated sodium carbonate loses water molecules upon heating. When this prepared anhydrous sodium carbonate is exposed to air it absorbs moisture from the air to form hydrous sodium carbonate. All three absorb air to form new products and get heavier and thus, do not lose weight.

A saturated solution of carbon dioxide loss weighs when exposed to air as carbon dioxide from the solution dies when exposed to air. Carbon dioxide gets absorbed by air and thus, the solution loses its weight as carbon dioxide gets absorbed by air or dies up in the atmosphere.
Thus, the correct option is D.

Note: Saturated solution of carbon dioxide so what is the meaning of saturated? Saturated solution means the solution containing solvent which is highly soluble in solution. So, in a saturated solution of carbon dioxide, carbon dioxide is mixed in as a solution let’s say water. This is forming soda, so the example of saturated solution carbon dioxide is soda or soft drink. When we open the bottle of soda in the air, all the carbon dioxide dies up in the air and the saturated solution loses its weight.