Properties of Water

Background

Water is a polar molecule, which means it has a positive end and a negative end. The oxygen end (blue) is like the negative pole and the hydrogen end (gray) is like the positive pole. Just like magnets, the positive end of one water molecule will attract the negative end of another water molecule resulting in the properties of adhesion, cohesion, and surface tension.

• Adhesion: the attraction of water molecules to other substances
• Cohesions: the attraction of water molecules to other water molecules
• Surface tension: the attraction of surface water molecules to other surface water molecules resulting in a surface “skin.”

Because of water’s unique molecular properties, its observable physical properties impact our daily lives in ways we don’t often notice. This activity provides you with visual and quantitative evidence of the phenomena of adhesion, cohesion, and surface tension in water. You will compare these properties of water for deionized water and deionized water with Dawn dish detergent added to make sense of how water’s polar nature determines its physical properties.

Standards

This activity addresses the following AP® Biology concepts:

• SYI-1 Living systems are organized in a hierarchy of structural levels that interact.
• SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect its biological function.
• SYI-1.A.3 The hydrogen bonds between water molecules result in cohesion, adhesion, and surface tension.