Properties of Water

• Water exhibits unique properties due to its molecular structure and hydrogen bonding.

Adhesion and Cohesion

• Adhesion: The attraction of water molecules to other surfaces, allowing it to form droplets on surfaces like glass or grass.

• Cohesion: The attraction of water molecules to one another, allowing them to stick together, creating surface tension.

• Example: Water adheres to blades of grass and also to itself, demonstrating both adhesion and cohesion.

Surface Tension

• Surface tension is the result of strong cohesive forces among water molecules at the surface, due to hydrogen bonds.

• The stronger the cohesive forces, the greater the surface tension.

• A water strider bug can walk on water due to the high surface tension, which can support small objects.

• Experiments such as the penny drop and pepper flakes demonstrate the effects of surface tension and hydrogen bonds:

  • Penny Drop: Water holds onto the penny until too much is added, demonstrating surface tension.

  • Pepper Experiment: Pepper flakes rest on the surface of water due to hydrogen bonds, showing cohesion and surface tension.

Role of Polarity in Water

• Polarity refers to the uneven distribution of charge within a water molecule (oxygen is slightly negative, hydrogens are slightly positive).

• This polarity leads to strong hydrogen bonding:

  • Polarity allows for hydrogen bonds to form between water molecules, increasing cohesion.

• Each water molecule can bond with multiple other water molecules through hydrogen bonds, contributing to the overall strength of the surface tension.

Capillary Action

• Capillary action is the ability of water to flow in narrow spaces without external forces, driven by adhesion and cohesion.

• This property allows plants to draw water upward through their roots and stems.

Specific Heat of Water

• Water has a high specific heat, meaning it resists rapid temperature changes.

• This property is due to the energy required to break hydrogen bonds.

• Compared to other liquids (e.g., oil), water takes longer to heat up and cool down due to its specific heat.

Summary of Key Concepts

• Polarity ➡ Hydrogen Bonding ➡ Cohesion ➡ Surface Tension: These concepts are interlinked; polarity creates hydrogen bonds, which enhance cohesion, ultimately leading to surface tension in water.