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Properties of Water

Biology: AQA A Level, topic 1.7.3

Useful Properties of Water

Water is a major component of cells and is essential to life as we know it (60–70% of the human body is made up of water). The properties of water that make it such a useful substance are:

Good metabolite

Good metabolite

  • Water is used or formed in many metabolic reactions, such as condensation and hydrolysis reactions.
  • ATP + H2O → ADP + Pi + energy
    • A bond is broken and a water molecule is used up and so this is a hydrolysis reaction.
  • ADP + Pi + energy → ATP + H2O
    • A new bond is formed and a water molecule is released and so this is a condensation reaction.
High heat of vaporisation

High heat of vaporisation

  • The specific latent heat of vaporisation is the amount of energy needed to change 1 kg of a liquid substance to a gas.
  • As liquid water heats up, hydrogen bonding makes it difficult to separate the water molecules from each other. This means that a lot of energy is needed for water to evaporate.
  • When water evaporates, energy is used up - this cools the environment where the evaporation is taking place.
  • This is why sweating helps with body temperature regulation.
High heat capacity

High heat capacity

  • Specific heat capacity is the amount of heat one gram of a substance must absorb or lose to change its temperature by 1oC.
  • Water has a high heat capacity so takes a long time to heat and cool.
  • The specific heat capacity of water is much larger than sand. This is why land cools faster than the sea.
  • Water is used by warm blooded animals to more evenly disperse heat in their bodies.
Good solvent

Good solvent

  • Water is a good solvent because ions and polar molecules can easily dissolve in it.
  • Water is a polar molecule. This means that the positive end of the water molecule attracts negative ions and the negative end will attract positive ions.
Cohesive properties

Cohesive properties

  • The strong attraction between water molecules due to hydrogen bonds is called cohesion.
  • Cohesion produces surface tension where water meets air.
  • This is why water forms droplets when placed on a dry surface rather than being flattened out by gravity.
  • Plants use this natural phenomenon to help transport water from their roots to their leaves.

Test yourself on Properties of Water

  • Water’s high heat capacity is caused by what?

  • What % of the human body is made up of water?

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