Classify each statement as an example of adhesion, cohesion, or surface tension.
A drop of water spilled on a table forms a drop on the table, rather than spreading out over the surface.
adhesion
Water molecules cling to plant cell walls.
Water molecules are attracted to each other.
cohesion
A water strider runs across a pond without breaking the surface.
Water molecules cling to the side of a beaker.
surface tension
A sewing needle floats when it is placed gently on top of water in a bucket.
The Correct Answer and Explanation is :
Statement Classification:
- A drop of water spilled on a table forms a drop on the table, rather than spreading out over the surface. – Cohesion
- Water molecules cling to plant cell walls. – Adhesion
- Water molecules are attracted to each other. – Cohesion
- A water strider runs across a pond without breaking the surface. – Surface Tension
- Water molecules cling to the side of a beaker. – Adhesion
- A sewing needle floats when it is placed gently on top of water in a bucket. – Surface Tension
Explanation:
Cohesion refers to the attraction between molecules of the same substance. For instance, when water forms drops on a table, it demonstrates cohesion because the water molecules prefer to stick together rather than disperse over the surface. This cohesive force is due to hydrogen bonding, a strong type of dipole-dipole interaction occurring between water molecules.
Adhesion is the attraction between molecules of different substances. This can be seen when water molecules cling to plant cell walls or the sides of a beaker. The interaction between water molecules and other materials can alter the way water behaves, adhering it to various surfaces rather than forming beads or droplets.
Surface tension is a physical property resulting from the cohesion of liquid molecules, characterized by the elastic-like force existing at the liquid-air interface. The example of a water strider moving across the surface of a pond without sinking exemplifies surface tension; the insect’s weight is not enough to overcome the strength of the hydrogen bonds between water molecules, allowing it to walk on water. Similarly, a sewing needle, when placed gently, can float despite being denser than water due to the surface tension keeping it afloat.
These properties of water are all manifestations of the polarity of water molecules, which features a partial negative charge near the oxygen atom and partial positive charges near the hydrogen atoms. This polarity allows water to engage in hydrogen bonding, which is crucial for the unique behaviors observed in cohesion, adhesion, and surface tension.
Image Generation:
Let’s create an image that visually depicts these concepts, focusing on surface tension with a water strider.
{
"prompt": "Illustration of a water strider walking on the surface of a pond, demonstrating the concept of surface tension. The image should show close-up details of the water strider's legs making contact with the water surface, which bends but does not break under the insect. The background should depict a serene pond setting with clear water and visible plant life around. The focus is on the physical interaction between the insect and the water surface, highlighting the strength of the water's surface tension.",
"size": "1024x1024"
}