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

The correct order of increasing boiling points for Ar, NH3, H2O, and NaCl is Argon (lowest boiling point due to dispersion forces), followed by Ammonia (hydrogen bonds), Water (extensive hydrogen bonds), and Sodium Chloride (an ionic compound with the highest boiling point).

Step-by-step explanation:

To order the substances H2O, NH3, Ar, and NaCl by expected increasing boiling points, we need to consider the types of intermolecular forces each substance exhibits. Argon (Ar) is a noble gas with very weak dispersion forces, so it has the lowest boiling point. Ammonia (NH3) exhibits hydrogen bonding but is less extensive than water due to having only one lone electron pair for hydrogen bonding. Water (H2O) also exhibits hydrogen bonding but to a greater extent, leading to a higher boiling point. Lastly, sodium chloride (NaCl) is an ionic compound, which has strong electrostatic interactions between ions, resulting in the highest boiling point.

Therefore, the correct order from lowest to highest boiling point is Ar, NH3, H2O, and NaCl, which corresponds to option 3.

Answer 2

Option (4) is correct

Step-by-step 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`