Which best explains the high surface tension of water? A. its high density B. its ion-dipole interactions C. its adhesive interactions D. its hydrogen bonding interactions
The Correct Answer and Explanation is:
The best explanation for the high surface tension of water is D. its hydrogen bonding interactions.
Water molecules exhibit strong hydrogen bonds due to the polarity of the water molecule. Each water molecule has a bent shape, with a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. This polarity allows each water molecule to form hydrogen bonds with neighboring molecules. A hydrogen bond is a weak attraction between a hydrogen atom attached to an electronegative atom (like oxygen) and another electronegative atom, creating a cohesive force that holds the molecules together.
At the surface of water, the molecules experience an imbalance in the forces acting on them. While water molecules inside the liquid are surrounded by other water molecules on all sides, molecules at the surface are only pulled inward by the hydrogen bonds of neighboring molecules, not outward. This results in the surface molecules experiencing a net inward force, which makes the surface of the water contract and resist external forces, contributing to the high surface tension.
Explanation of Other Choices:
- A. its high density: Water does have a relatively high density, but this is not the primary factor contributing to its surface tension. Density refers to the mass per unit volume and does not directly affect the cohesive forces at the surface.
- B. its ion-dipole interactions: Ion-dipole interactions occur when ions interact with polar molecules. While these interactions can be important in aqueous solutions, they do not directly explain the surface tension of pure water. Surface tension is more related to the cohesive forces between water molecules themselves, not ions.
- C. its adhesive interactions: Adhesive interactions refer to the attraction between water molecules and other substances (e.g., glass). While adhesive forces can influence phenomena like capillary action, the surface tension of water itself is primarily governed by the cohesive hydrogen bonds between water molecules.
Thus, the key factor contributing to water’s high surface tension is its hydrogen bonding interactions.
