Presentation on water and its properties
OBJECTIVE: Explain how hydrogen bonding occurs between water molecules and relate the
properties of water to its role in living organisms, limited to solvent action, high specific heat
capacity and latent heat of vaporisation
Hydrogen Bonding in Water
Water (H₂O) is a polar molecule, meaning it has a partial positive charge on one side (the
hydrogen atoms) and a partial negative charge on the other side (the oxygen atom). This
polarity allows water molecules to form hydrogen bonds with each other.
How Hydrogen Bonding Occurs:
1. Polarity: The oxygen atom in a water molecule is more electronegative than the
hydrogen atoms. This means it attracts electrons more strongly, creating a partial
negative charge (δ−\delta^-) on the oxygen and partial positive charges (δ+\delta^+)
on the hydrogen atoms.
2. Attraction: The partial positive charge on the hydrogen atoms of one water molecule
is attracted to the partial negative charge on the oxygen atom of another water
molecule.
3. Formation: This attraction forms a weak bond called a hydrogen bond. Each water
molecule can form hydrogen bonds with up to four other water molecules, creating a
network of interconnected molecules.
Properties of Water and Its Role in Living Organisms
1. Solvent Action Water is often referred to as the "universal solvent" due to its ability
to dissolve a wide range of substances. This property is crucial for many biological
processes.
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Mechanism: Water's polarity allows it to surround and separate individual ions and
molecules in a substance, effectively dissolving them.
Biological Importance:
o Nutrient Transport: Water dissolves essential nutrients, vitamins, and
minerals, allowing them to be transported through the bloodstream to cells and
tissues.
o Waste Removal: Metabolic waste products are dissolved in water and
excreted through urine.
o Chemical Reactions: Many biochemical reactions occur in aqueous
environments, where reactants are dissolved in water.
2. High Specific Heat Capacity Specific heat capacity is the amount of heat energy
required to raise the temperature of a substance by a certain amount.
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Mechanism: Hydrogen bonds absorb heat energy, which increases the kinetic energy
of water molecules. This absorbed energy is used to break hydrogen bonds rather than
increase temperature.
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Biological Importance:
o Temperature Regulation: Water's high specific heat capacity helps stabilize
temperatures in organisms and environments. This is vital for maintaining
homeostasis and ensuring that enzymes and biochemical reactions function
optimally.
o Climate Moderation: Large bodies of water, like oceans and lakes, absorb
and store heat, moderating the climate and reducing temperature fluctuations.
3. Latent Heat of Vaporisation Latent heat of vaporisation is the amount of heat
energy required to change a substance from a liquid to a gas without changing its
temperature.
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Mechanism: During vaporisation, hydrogen bonds between water molecules must be
broken. This process requires a significant amount of energy.
Biological Importance:
o Cooling Mechanism: When water evaporates from the surface of an organism
(e.g., sweating in humans), it absorbs heat energy from the body, providing a
cooling effect. This helps regulate body temperature.
o Transpiration in Plants: Water vaporises from the leaves' surface through
transpiration, which helps cool the plant and maintains the flow of water and
nutrients from roots to leaves.