Question

Hydrogen bonds cause surface tension in water, allowing some small organisms, like water striders, to move around on the surface of the water without getting wet. If you introduce soap (a large compound made up of polar covalent bonds) to the water, the surface tension disappears, and the water striders will sink into the water. This is because...

1) Water striders can't swim
2) Water makes hydrogen bonds with the soap instead of with itself, disrupting the surface tension
3) Soap dissociates in the water, becoming an electrolyte, and disrupting the surface tension
4) Soap creates new covalent bonds with water, becoming non-polar so surface tension disappears
5) None of the above

Answer 1

Soap reduces the surface tension of water by disrupting the cohesive hydrogen bonds between water molecules, allowing water to bond with the soap instead, which explains why soap causes water striders to sink.

Step-by-step explanation:

Surface tension in water is caused by the cohesion of water molecules, which happens due to hydrogen bonding. These hydrogen bonds give water the ability to maintain a firm surface that organisms, like water striders, can traverse. When soap is introduced into the water, it disrupts this surface tension, causing the water striders to sink. The effect occurs because soap molecules have a polar end that is attracted to water and a non-polar hydrocarbon tail that is repelled by water. As soap molecules spread across the water surface, the non-polar tails disrupt the network of hydrogen bonds between water molecules, thus reducing the surface tension.

The correct explanation for why soap causes water striders to sink is that water makes hydrogen bonds with the soap instead of with itself, disrupting the cohesion and surface tension that normally allow the water strider to stay atop the water's surface. This is indeed what happens according to choice (2) in the student's options.