Question

a student places a small amount of water in a glass dish and then carefully places a small paperclip on the surface of the water. the paperclip floats. what happens if the student adds a drop or two of dish soap to the water? choose three correct answers.

• the soap decreases the surface tension of the water.
• the soap acts as a surfactant.
• the soap increases the surface tension of the water.
• the paperclip falls through the water to the bottom of the dish.

Explanation:

Analyze the physical phenomenon

Using the Surface Tension Causes knowledge point:
The floating paperclip is supported by the surface tension of water, which arises from cohesive intermolecular forces between water molecules at the surface.

Analyze the effect of adding soap

Using the Surfactants knowledge point:
Dish soap molecules have hydrophilic heads and hydrophobic tails. When added to water, they disrupt the hydrogen bonding network at the surface, acting as a surfactant and decreasing the surface tension.

Determine the outcome for the paperclip

With the surface tension significantly reduced, the upward force supporting the paperclip is lost, causing the paperclip to sink to the bottom of the dish.

Answer:

• The soap decreases the surface tension of the water. (Correct answer)
• The soap acts as a surfactant. (Correct answer)
• The soap increases the surface tension of the water.
• The paperclip falls through the water to the bottom of the dish. (Correct answer)