2.2: Water What do you know about water? 5 min. discussion What are the uses of water in the human body?

Experiment: Regulation of human body temperature through sweat production Find details for this task on moodle

Polarity Covalent 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 Sometimes referred to as dipolarity

Hydrogen bonds The attraction between the water molecules Technically NOT a bond – an attraction Weak intermolecular force, BUT water molecules are very small  LOTS of H-bonds. Moly mods? Build a tetrahedral structure? Each water molecule can form four hydrogen bonds Important to remember: H-bonds are a theory, scientists cannot prove they exist. But, it has not been disproved, and the presence of H-bonds helps to explain the unique properties of water.

Solvent properties Water 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 capacity A (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 capacity Latent 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 point Water is liquid over a wide range of temperatures 0 – 100 degrees C. Most habitats are within this range.

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Comparing the thermal properties of water and methane Read orange box pg. 71. Write a summary paragraph.

Hydrophilic V’s 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 In water, hydrophobic substances will be attracted to each other (this is due to the water molecules surrounding the substance being more attracted to each other (forming hydrogen bonds) than they are to the hydrophobic/non polar substance. This ‘clumping’ together of non polar substances in water is known as hydrophobic interaction.

*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