2.3 Properties of Water

Tell me about the Structure of Water. What is its importance to life?

Water is polar because it has a slight charge difference across different poles of molecule (dipole)

This allows water to form weak associations (H bonds) with other polar or ionic molecules

Hydrogen bonding and the angular shape of a water molecule gives it unique properties essential to existence of living things

What are the Unique Properties of Water?

1. Water is an excellent solvent

2. Water is both adhesive and cohesive

3. Water has a high specific heat capacity

4. Water has a high heat conductivity

5. Water has a high boiling/freezing point

6. Water is more dense as a liquid then as a solid

What is a solvent?

substance that is able to dissolve other substances

Tell me about Water being a good solvent. What is an example of it being helpful within life?

Water is a polar molecule

• Break ionic bonds

Hydrophilic “water loving” - substances that freely associate and readily dissolve in water (all polar molecules and ions)

Hydrophobic “water hating” - substances that do not freely associate and readily dissolve in water (fats and oils)

e.g. Water soluble substances (NaCl, O2, glucose, ionized aa) can travel freely in blood plasma, whereas water insoluble substances (lipids) cannot (form complexes with proteins - lipoproteins)

Tell me about Water being Adhesive and Cohesive. What is an example of it being helpful within life?

Adhesive - tendency of dissimilar particles/surfaces to cling to one another (plants can get water throughout their system via capillary action)

Cohesive - tendency of similar or identical particles/surfaces to cling to one another (our blood is able to move smoothly through vessels)

What is Specific Heat Capacity? What is an example of water’s specific heat capacity being helpful within life?

amount of energy needed to change the temperature of 1 kg of a substance by 1°C

Water is slow to change temperature

H-bonds broken before change state (absorb heat)

e.g temperature regulation

What about water’s high heat conductivity? What is an example of water’s high heat conductivity being helpful within life?

Since water has strong H-bonds, when heat is applied, energy is absorbed into breaking the bonds, and the increased kinetic energy is efficiently transferred through hydrogen bonding meaning

water takes in a lot of energy without changing state

e.g. also temperature regulation as if you are cold you can heat yourself up quickly.

Tell me about water’s high boiling/freezing points. How is it good for life?

• Boiling Point: The high boiling point of water results from the need to break numerous hydrogen bonds before transitioning from a liquid to a gas.

• Freezing Point: Water's freezing point is elevated due to the formation of a stable and structured network of hydrogen bonds in the liquid state before transitioning to the solid state.

e.g. your blood won’t turn to gas just because its summertime or freeze because it’s winter

Tell me about water being denser as a liquid than solid. How is water’s density good for life?

• Water molecules form a hexagonal lattice structure when transitioning from a liquid to a solid state.

• Hydrogen bonds cause molecules to arrange themselves with slightly more space in a solid (ice) compared to a liquid (water).

e.g. during winter, lakes can freeze over and life will survive

Summary

Property	Attributes	Significance
Solvent	Dipolarity means water can dissolve molecules that are polar or charged	Water is a good transport medium (e.g. the blood system can transport soluble materials in its plasma)
Adhesive	Dipolarity means water will stick to surfaces that are polar or charged	Water can move via capillary action against gravity (e.g. water can move up the xylem via transpiration)
Cohesive	Dipolarity means water will stick to other water molecules (via H-bonds)	Water has a high surface tension, allowing small organisms to move on its surface (e.g. Basilisk lizard)
Thermal	Extensive hydrogen bonding means water can absorb a lot of heat before changing state	Water is an excellent coolant (e.g. sweat) Water is a good medium for metabolic reactions (absorbs heat from exothermic reactions)
Density	Water is less dense as a solid than as a liquid (maximum density ~ 4°C)	Ice floats on water (prevents oceans from freezing as ice layer prevents exposure to cold temperatures)
Transparency	Water is transparent to visible spectrum	Aquatic plants can undergo photosynthesis