9700 · 2.4
Water flashcards
Revision flashcards for Cambridge 9700 Water (syllabus 2.4). Flip, recall, then mark a real past-paper question.
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Why is a water molecule described as polar?
Due to an unequal sharing of electrons between the oxygen and hydrogen atoms. The oxygen atom is more electronegative, resulting in a slight negative charge (δ-), while the hydrogen atoms have slight positive charges (δ+).
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What is a hydrogen bond in the context of water?
A weak electrostatic attraction between the slight positive charge (δ+) on a hydrogen atom of one water molecule and the slight negative charge (δ-) on the oxygen atom of a neighbouring water molecule.
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What is meant by water's high specific heat capacity?
It means a large amount of heat energy is required to raise the temperature of 1 kg of water by 1°C (approx. 4.2 kJ). This is due to the extensive hydrogen bonding that must be broken.
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Explain the biological significance of water's high latent heat of vaporisation.
A large amount of energy is needed for water to evaporate. This provides an effective cooling mechanism for organisms (e.g., sweating in mammals, transpiration in plants) as the evaporating water removes significant heat from the body.
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Why is water an excellent solvent for many biological molecules?
Its polarity allows it to form hydrogen bonds with other polar molecules (e.g., glucose) and surround ions (e.g., Na⁺, Cl⁻), forming hydration shells and dissolving them. This makes it a key transport medium and the site of metabolic reactions.
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Define cohesion and adhesion of water and state their importance in plants.
**Cohesion:** Attraction between water molecules. **Adhesion:** Attraction between water molecules and other surfaces. Together, they create the continuous transpiration stream in the xylem, allowing water to move from roots to leaves against gravity.
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Why does ice float on liquid water and why is this important for aquatic life?
As water freezes, molecules form a crystalline lattice, which is less dense than liquid water. Ice floating on ponds and lakes provides an insulating layer, preventing the entire body of water from freezing and allowing aquatic organisms to survive underneath.
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What is the role of water as a metabolite in a hydrolysis reaction?
In hydrolysis, a water molecule is used to break a chemical bond, splitting a large polymer into smaller monomers. For example, the digestion of starch into glucose.