When methanol (CH3OH) is mixed with water (H2O), the strongest intermolecular forces which result between a molecule of water and a molecule of methanol are:  A: hydrogen bonds B: ion-dipole C: induced dipole – induced dipole interactions (dispersion forces) D: dipole-dipole When methanol (CH3OH) is mixed with water (H2O), the strongest intermolecular forces which result between a molecule of water and a molecule of methanol are:  A: hydrogen bonds B: ion-dipole C: induced dipole – induced dipole interactions (dispersion forces) D: dipole-dipole
The Correct Answer and Explanation is :
Correct Answer: A: Hydrogen bonds
Explanation:
When methanol (CH3OH\text{CH}_3\text{OH}) is mixed with water (H2O\text{H}_2\text{O}), the strongest intermolecular forces between the molecules are hydrogen bonds. Here’s why:
1. Structure and Polarity of Methanol and Water:
- Methanol consists of a hydroxyl group (−OH-\text{OH}) attached to a methyl group (CH3\text{CH}_3).
- Water is composed of two hydrogen atoms covalently bonded to an oxygen atom.
- Both methanol and water are polar molecules. They have significant electronegativity differences between oxygen and hydrogen, making their bonds polar.
2. Hydrogen Bonding in Methanol and Water:
- Hydrogen bonding occurs when a hydrogen atom bonded to a highly electronegative atom (like oxygen, nitrogen, or fluorine) interacts with a lone pair of electrons on another electronegative atom.
- In both methanol and water, the oxygen atom has lone pairs, and the hydrogen atoms bonded to oxygen are partial positively charged (δ+\delta^+). This enables the formation of hydrogen bonds between:
- The hydrogen atom in the −OH-\text{OH} group of methanol and the oxygen atom of water.
- The hydrogen atom of water and the oxygen atom of methanol.
3. Why Not Other Intermolecular Forces?
- Ion-dipole (B): This occurs between ions and polar molecules. Methanol and water do not ionize under normal conditions, so this force is not applicable.
- Induced dipole-induced dipole (C): Also called London dispersion forces, these are weaker and present in all molecules but not the strongest force here.
- Dipole-dipole (D): While both methanol and water are polar, dipole-dipole interactions are weaker than hydrogen bonds.
4. Conclusion:
The strongest intermolecular forces between methanol and water are hydrogen bonds due to the presence of highly electronegative oxygen atoms and hydrogen atoms available for bonding. These interactions are responsible for their high miscibility and unique physical properties.