Key Questions How can you account for the high surface tension and low vapor pressure of water? How would your relate the structure of ice to that of water and water vapor?

Vocabulary Surface tension Surfactant Vapor pressure

Introduction

Water in the liquid state… Besides just the water on the surface, water exists in huge quantities underground too! Ice vs. salt water Unique properties: High surface tension Low vapor pressure Boils easily Vaporizes/evaporates relatively easily Hydrogen Bonding

Surface Tension The inward force, or “pull” that tends to minimize the surface area of a liquid All liquids have surface tension, some have higher tensions than others Surfactants are substances tat interferes with the hydrogen bonding between water molecules thereby reducing the surface tension

Demonstration of Surface Tension

Vapor Pressure Vapor pressure: result of molecules escaping from the surface of the liquid to enter the vapor phase Why would the vapor pressure be low? What would happen if water did not have a low vapor pressure and instead had a high Vapor Pressure?

Water in the solid state… Have you ever filled a glass with water and placed it in the freezer? What happened? As water begins to cool, it initially acts like a typical liquid. It slowly contracts and its density gradually increases. But then below 4 o C, the density no longer increases, but begins to decreases. This is the reason ice floats! But why…?

Water in the solid state… The structure of ice is a regular open framework of water molecules arranged like a honeycomb! The particles actually spread out more than the liquid state, which is weird!

Check Quiz 1. What causes the high surface tension and low vapor pressure of water? 2. How would you describe the internal arrangement of ice particles? 3. What effect do surfactants have on liquids? 4. Why does water form “droplets”? 5. The molecules of water and methane (CH 4 ) have similar masses, but methane changes from a gas to a liquid at -161 o C. Water becomes a gas at 100 o C. What could account for the difference?