2.2: Water

Experiment: Regulation of human body

temperature through sweat production

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PolarityCovalent bonds BUT

electrons are NOT equally shared

It is a POLAR covalent bond

Oxygen exerts a greater pull on electrons than Hydrogen

Therefore, electrons move closer to Oxygen

Oxygen = negative charge

Hydrogen = positive charge

Hydrogen bondsThe attraction between the water molecules

Technically NOT a bond – an attraction

Weak intermolecular

force, BUT water molecules are very small LOTS of H-

bonds.

Solvent propertiesWater is an excellent solvent.

Forms hydrogen bonds with polar molecules.

Both positive and negative ions are able to dissolve.

Cohesive & Adhesive properties

Cohesion = when two of the same type of molecule bind together

Adhesion = two molecules, of different types bind together

Cohesion Adhesion

Water transport in plants – suction force through xylem ‘pulls’ water molecules upwards. Cohesion insures water molecules do not separate.

Maintain moisture in the leaves of plants. Water molecules ‘stick’ to cellulose molecules to prevent water loss.

Thermal properties

• High specific heat capacityA (relatively) large amount of energy is required to raise and lower the temperature of water. As a result, water is a (relatively) thermally stable environment.

• High latent heat capacityLatent heat of vaporization = amount of heat required to evaporate a liquid. In water (due to H-bonds) the amount of energy required is high, therefore evaporation has a cooling effect.

More thermal properties…

• High boiling pointWater is liquid over a wide range of temperatures 0 – 100 degrees C. Most habitats are within this range.

Comparing the thermal properties of water and

methane

Read orange box pg. 71. Write a summary paragraph.

Hydrophilic V’s Hydrophobic

Hydrophilic Hydrophobic

Water ‘loving’ Substances are chemically attracted to water.Polar substances.Anything that dissolves in water.Anything that adheres to water.

Water ‘fearing’ Insoluble in water (can dissolve into other substances.Non-polar (uncharged) substances.

e.g. glucose, cellulose All lipids

*this question is from the OLD syllabus

International mindedness

There are challenges for the increasing human population in sharing water resources equitably for drinking and irrigation, electricity generation and a range of industrial and domestic processes

Design an experiment to investigate the solubility

of water

Thermal properties – water/methane comparison data