What types of intermolecular forces exist between CH3OH and H2O?
The correct answer and explanation is:
Correct Answer: The intermolecular forces that exist between CH₃OH (methanol) and H₂O (water) are hydrogen bonding, dipole-dipole interactions, and London dispersion forces.
Explanation:
Intermolecular forces are the attractive forces that occur between molecules, and they determine many physical properties such as boiling point, solubility, and vapor pressure. When methanol (CH₃OH) and water (H₂O) interact, several types of intermolecular forces can be observed.
The strongest force between CH₃OH and H₂O is hydrogen bonding. Both methanol and water have -OH (hydroxyl) groups. In methanol, the oxygen atom is bonded to a hydrogen atom, just as in water. The hydrogen atom in one molecule can form a hydrogen bond with the lone pair of electrons on the oxygen atom of the other molecule. This mutual ability to donate and accept hydrogen bonds allows strong hydrogen bonding interactions to occur between CH₃OH and H₂O molecules.
In addition to hydrogen bonding, dipole-dipole interactions are present. Both CH₃OH and H₂O are polar molecules. In methanol, the electronegative oxygen creates a partial negative charge near itself and a partial positive charge near the hydrogen. Water also has a permanent dipole. The partial charges in these molecules attract each other, resulting in dipole-dipole attractions.
Lastly, London dispersion forces also exist between CH₃OH and H₂O. These are the weakest intermolecular forces and occur between all molecules, whether they are polar or nonpolar. They arise from the temporary movement of electrons that create instantaneous dipoles.
The combination of these three types of forces—hydrogen bonding, dipole-dipole, and London dispersion—makes the interaction between methanol and water particularly strong. This explains why methanol is completely miscible in water, forming a uniform solution.