Question

Which gas is most soluble in water?
a.) He
b.) \[{{H}_{2}}\]
c.) $N{{H}_{3}}$
d.) $C{{O}_{2}}$

Answer 1

Hint: To comment about solubility, we must be aware of the polar and nonpolar molecules because they play an important role in solubility. As we are aware of the fact – like dissolves like. So the concept of polarity is important for this question.

Complete step by step answer:
-Based on polarity, the molecules can be divided into 2 parts- polar and nonpolar molecules. Polar molecules are those which have a net dipole moment due to the differences in the electronegativities of the atoms present in the molecule which do not allow to cancel the dipoles.
Non-polar molecules are those which have net dipole moment as zero as the dipoles of the atoms are cancelled out within the molecule
-Polar bonds have a net dipole moment and they generally are formed when there is no symmetry present within the molecule. With no symmetry, the dipole moments of different atoms do not cancel out each other thus leading to a net dipole moment.
-Non-polar bonds do not have any net dipole moment and are generally formed in the compounds where there is a presence of symmetry. Even if the atoms have a net dipole moment, the overall dipole moment of the compound is zero because they cancel each other.

-Some examples of polar molecules are $HF,HCl,{{H}_{2}}O,N{{H}_{3}}$
The orientation of the dipole moment can be shown as $H\to Cl,H\to F$

Some examples of non-polar molecules which are caused due to symmetry are $CC{{l}_{4}},C{{H}_{3}}C{{H}_{2}}C{{H}_{3}}$, O=C=O, O=O

-Ability to be dissolved in a solvent is called solubility. The compound that dissolves a substance is called solvent and the substance that gets dissolved is called solute. Polar solvents can dissolve polar substances easily as they form polar bonds or hydrogen bonds with one another. Non-polar substances readily dissolve in non-polar solvents.
-In the question, we have been given different gases and we need to see which one dissolves in water. For that, we must first find out which gases are polar and which are non-polar. Water is a non-polar solvent due to the difference in the electronegativities of H and O atoms present in water molecules.
-So. The easiest way to solve this question is by finding which of the given gases are polar in nature because only they will be easily soluble in water. The polarity can also be checked by the presence of symmetry within the molecule.

-Helium is an inert gas and is monatomic in nature. Due to its inert nature, it is non-polar as it has complete electrons in its shell and has complete octet. So, it is not soluble in water.

-Hydrogen is a diatomic gas and is present in nature as \[{{H}_{2}}\]. If we draw its structure, we can see that it is also a nonpolar gas as it is made up of a single atom which is symmetrical in nature. So it cannot be polar as no orientation of electrons occur in any direction.

-Ammonia is a gas which is made up of 2 different atoms, hydrogen and nitrogen and its chemical formula is given as $N{{H}_{3}}$.
Nitrogen atoms have a high value of electronegativity and so it attracts the shared pair of electrons towards itself. Thus ammonia is polar in nature and so it easily dissolves in water. As ammonia contains nitrogen atoms, it makes hydrogen bond with water. This results in high solubility of ammonia in water as hydrogen bond is comparatively stronger.

-Carbon Dioxide gas also has 2 atoms in it, carbon and oxygen and its structure is represented as O=C=O. Oxygen atoms are more electronegative than carbon atoms. Yet it is a nonpolar gas because it shows symmetry in its structure. So, it is not a polar molecule.
So, the correct answer is “Option C”.

Note: Helium and its compounds are least soluble in water or any other solvent. No single gas exists which has lower solubility than helium. Also, solubility of gases increases with an increase in pressure and decrease with the increase in temperature.