How Does Water Affect Electrostatic Interactions?

Coulomb’s law explains the force between two charged particles, but the solvent environment plays a crucial role in determining the strength of this interaction. In water, electrostatic interactions are significantly weaker than in a vacuum due to its high dielectric constant.

Given Data and Explanation

1. Point charges are 5.5 Å apart in vacuum.
2. Energy of interaction in vacuum = 60 kcal/mol.
3. Dielectric constant of water at 20°C = 80.

The energy of interaction in a medium with a dielectric constant (D) is calculated as:

Fm= Fair/ D

Substituting the given values:

                     Fm= 60 /80

Correct Answer: 0.75 kcal/mol (Option 3)

Why Water Weakens Electrostatic Interactions

• Water has a high dielectric constant (80), reducing electrostatic attraction between charges.
• Charged particles in water experience shielding, weakening their interaction.
• In biological systems, this property is essential for molecular stability, protein folding, and ion transport.

Why Other Options Are Incorrect

• 4800 kcal/mol (Option 1):
  • Incorrect, as water weakens interactions rather than strengthening them.
• 60 kcal/mol (Option 2):
  • Incorrect, as this is the interaction energy in a vacuum, not in water.
• 140 kcal/mol (Option 4):
  • Incorrect, as the interaction energy significantly decreases in water.

Conclusion: Water Reduces Electrostatic Attraction

In aqueous environments, ionic interactions are significantly weaker than in vacuum due to water’s high dielectric constant. This principle is crucial in biochemistry, electrochemistry, and drug design, where solvent effects determine molecular behavior.