2.2 PROPERTIES OF WATER

Water is a Polar Molecule

This means there is an uneven distribution therefore water has a partial negative charge at the oxygen atom and partial positive charge at the hydrogen atoms

Hydrogen Bonds are attractions between Polar Molecules

Hydrophilic: Substances that are chemically attracted to water

Hydrophilic substances include:

• All substances that dissolve in water such as glucose
• Particles with positve or negative charges such as sodium and cholride ions
• Substances that water adheres to such as cellulose

Hydrophobic: Substances that are insoluble in water

Hydrophobic substances include:

• Substances that do not have positive or negative charges
• Nonpolar substances
• Substances that dissolve in other solvents

Water is Cohesive - Water molecules cohere (stick to each other)

This property results from the polarity of the water molecule and water's ability to form hydrogen bonds

Hydrogen bonds are weak, however the large number of Hydrogen bonds present gives great strength to the Cohesion Property

Benefit of Cohesion: Coloumns of water can be sucked to the top of trees in tubes called Xylem Vessels because of the strong pulling force of Cohesion

Water is Adhesive - Water is a Polar Molecule and has a large number of Hydrogen bonds

The large number of Hydrogen Bonds gives Water great Adhesive strength

Water molecules can therefore adhere to surfaces (stick to surfaces)

Benefit of Water's Adhesion: Adhesive forces between water and cellose in cell walls of leaves cause water to be drawn out of the xylem vessels this keeps the cells walls moist to maintain the ability to act as a gas exchange surface

Many substances dissolve in water due to polarity (partial positive and negative charge)

Benefit of Solvent Property: Water is a medium for metabollic reactions where all polar substances involved dissolve in water.

Temperature of Water remains relatively stable

Water has a high specific heat capacity this means that a lot of energy is required to change the temperature

Water's high specific heat capacity is due to the many Hydrogen Bonds

Water has a high latent heat of vapourization this means that a lot of energy is required to change state from liquid to gas

Water also has high melting and boiling points (100°)

Benefit of Thermal Property: Water is liquid in most habitats on Earth this makes it suitable for living organisms. High specific heat capacity allows for a stable habitat because temperature change is slow. High latent heat of vapourization makes water an effective coolant for animals (sweat) and plants (transpiration)