Question

Arrange the molecules H2O, NH3, Ar, NaCl in order of expected increasing boiling points. 1. None of these 2. NaCl, H2O, NH3, Ar 3. Ar, NH3, H2O, NaCl 4. NH3, Ar, H2O, NaCl

Answer 1

Answer:

Option (4) is correct

Explanation:

• NaCl is an ionic solid. $Na^{+}$ and $Cl^{-}$ ions are held together by strong coloumbic attractive force. Hence NaCl has highest boiling point'
• Ar is a monoatomic molecule. Hence only weak london dispersion force exists between Ar atom/molecules. Hence it requires lowest amount of energy to boil and thereby possess lowest boiling point.
• $NH_{3}$ and $H_{2}O$ are polar protic molecules. Hence they possess london dispersion force, dipole-dipole force and hydrogen bonding as intermolecular forces.
• Dipole-dipole force is stronger in $H_{2}O$ than $NH_{3}$ due to more polar O-H bond than N-H bond. Also molecular weight of $H_{2}O$ is higher than $NH_{3}$. So, more energy is required to boil $H_{2}O$. So, $H_{2}O$ has higher boiling point than $NH_{3}$

Hence order of boiling point : $NaCl>H_{2}O>NH_{3}>Ar$