Water

Question 1

Water

Answer 1

• 2 hydrogen atoms covalently bonded to an oxygen atom (H2O)
• major component in cells
• most abundant liquid on earth
• Dipolar molecules
• About 60-70% of your body is water

Question 2

Dipolar water molecule

Answer 2

• water has 2 charges (a positive and negative pole)
• It has an unevenly distriputed charge: oxygen atom is slightly negative and the hydrogen atom is slightly positive

Question 3

Hydrogen bonding

Answer 3

• O bonds on negative pole will attact to H bonds on positive pole of another water molecule
• Attractive force is hydrogen bonding
• Each single bond is weak
• Numerous H bonds in water make it a stable structure

Question 4

What are the properties of water?

Answer 4

1. High specific heat capacity
2. High latent heat of vapourisation
3. Strong cohesion
4. Solvent
5. Metabolite

Question 5

Specific heat capacity of water

Answer 5

SHC= amount of energy required to raise 1kg of a substance by 1 degree * Water molecules can move past each other and stick together, as its a liquid
* H- bonds are continually made and broken
* It takes more heat energy to break these H-bonds so water has a high boiling point of 100 degrees
* SHC of water = 4200 j/kg degrees C
* This means that water is able to resist temperatur changes, providing a stable environment within cells + for aquatic organisms
* It buffers organisms against sudden temperature changes to maintain a stable environment for enzyme function

Question 6

Latent heat of vaporisation

Answer 6

amount of energy needed to vapourise 1g of a substance
* In order for water to change state from a liquid to a solid, H- bonds must be broken
* A lot of enegy is required to break the H bonds so water has a high latent heat of vapourisation
* If temperatures continue to rise, water molecules escape to become gases decreasing the kinetic energy in the molecules remaining
* This leads to the coolling effect
* COOLING EFFECT= the result of evaporation where some molcules evaporate and the remainder have reduced temperature
* E.g humans sweat to reduce body temperature and plants transpire

Question 7

Water in metabolism

Answer 7

• Used to break down large, complex molexules by hydrolysis
• e.g proteins into amino acids, sugars into monosaccharides
• Produced in condensation reactions
• Chemical reactions take place in an aqueous medium
• Major raw material in photosynthesis

Question 8

Water as a solvent

Answer 8

• Aqueous solutions are formed when solutes are dissolved in water
• water is a universal solvent
• It can be used as transport medium for solutes
• It dissolves:
  – gases such as o2 and CO2 in blood
  – wastes such as ammonia and urea
  – inorganic ions and small hydrophyliic molecules such as amino acids, monsaccharides anf ATP
  – enzymes

Question 9

Cohesion of water

Answer 9

tendancy of water molecules to stick together
* Hydrogen bonding means water has large cohesive forces
* This allows water to be pulled from one end of a tube to another end
* E.g plants draw water up xylem vessels in a contiouous stream against the pull of gravity
* Surface tension is created where water molecules meet air
* Water surface acts as a skin and is strong enough to support small organisms e.g pond skaters