The Properties of Water

prerequisite review

What unique feature of water molecules leads to properties like cohesion, adhesion, and high surface tension?

• Hydrogen bonds (H bonds), which

• Bonds form between partial (+) charge of hydrogen of one water molecule and the partial (-) oxygen of another due to water's polarity

What is solubility in water

The ability to dissolve many substances (making it a universal solvent),

What causes the solubility in water?

• Its polarity and H bonding that attract/surround solute molecules

• Example: NaCl + H₂O → Na⁺ + Cl⁻.

What is the biological purpose of water's solubility?

• allows chemical reactions to occur more frequently

• this helps organisms respond quickly to their environment.

What is cohesion and adhesion in water?

• Cohesion = Water molecules stick to each other via hydrogen bonds.

• Adhesion: Water sticks to other polar surfaces due to polarity

What is the biological purpose of cohesion and adhesion in water?

• allow for capillary action (water sticks/moves up the walls of the capillary)

• Effective transport of nutrients/waste within an organism

What is surface tension in water, and what causes it?

• Water molecules cling tightly to each other at the surface

• creates a "skin" because they're more attracted to each other than to air.

What is the biological purpose of surface tension?

• explains how water-striding insects can walk on water

• supports small organisms or objects on the surface.

What is high heat capacity in water, and what causes it?

• Water's ability to absorb a large amount of heat w/o changing its chemical state/temp

• due to hydrogen bonds requiring energy to break.

What is the biological purpose of high heat capacity?

• stabilizes temperatures in bodies of water

• helps organisms maintain normal internal thermal temperatures.

How does water's density change with temperature, and what happens with ice?

• Depends on temperature

• as water cools and expands (especially when freezing) this decreases

• Ice is expanded and less dense, so it floats.

What is the biological purpose of water’s density?

• The ice floats and acts as an insulator on bodies of water

• this protects aquatic organisms below and allows them to survive winter.

List the main properties of water

• Unique H bonds

• cohesive/adhesive

• universal solvent

• high surface tension

• high heat capacity

• density depends on temp (expansion = lower density)

• quite polar

• Molecules cling together; adhesion from polarity