How does the addition of soap affect the surface tension of water?

• A. Soap has no effect on the surface tension of water.
• B. Soap causes water to evaporate more quickly, which increases surface tension.
• C. Soap decreases the surface tension of water by disrupting hydrogen bonding between water molecules.
• D. Soap increases the surface tension of water by strengthening hydrogen bonds.

Answer: (C)

Verified step by step guidance

1. Understand that surface tension is the result of cohesive forces between liquid molecules, primarily hydrogen bonding in water.
2. Recognize that soap molecules are surfactants, meaning they have both hydrophobic (water-repelling) and hydrophilic (water-attracting) parts.
3. When soap is added to water, the soap molecules position themselves at the surface, disrupting the hydrogen bonding network among water molecules.
4. This disruption reduces the cohesive forces at the surface, thereby lowering the surface tension of water.
5. Therefore, the addition of soap decreases the surface tension of water by interfering with the hydrogen bonds between water molecules.