Water

• What is water made from?

  1 oxygen and 2 hydrogen atoms held together by covalent bonds.
• Which atom's nucleus do the shared electrons move nearer to and why?

  Oxygen - it has a stronger positive charge so the negative electrons are more attracted to it.
• What effect does the shared electrons being attracted to one atom have on both atom charges?

  Oxygen becomes more negative (delta negative)

  Hydrogen becomes more positive (delta positive)
• What is a hydrogen bond?

  The electrostatic attraction between a slightly positive charge on an atom of one molecule and the slightly negative charge on another.
• How are hydrogen bonds represented in a diagram?

  Dotted lines
• Is an individual hydrogen bond strong or weak?

  It is a weak intermolecular force.
• What is specific heat capacity?

  The amount of energy required to raise the temperature of one gram of a substance by 1 degree C.
• Does water have a high or low specific heat capacity and why?

  (Relatively) high - there are many hydrogen bonds between particles that require lots of energy to break before the particles can gain kinetic energy, move faster and therefore increase in temperature.
• Why is water's specific heat capacity important to living things?

  Water resists temperature changes, acting as a buffer. In living things this means that it buffers internal temperature changes, aiding thermoregulation, maintaining optimum conditions for enzyme activity.
• What is latent heat of vaporisation?

  The amount of energy required to change the state of 1 gram of a liquid, to a gas.
• Does water have high or low latent heat of vaporisation and why?

  (Relatively) high - the hydrogen bonding between water molecules means that a lot of energy is required to break the many bonds and enable the water molecules to move away from each other, so that the change of state occurs.
• Why is water's latent heat of vaporisation important to living things?

  The evaporation of water has a large cooling effect. When a mammal sweats, a large amount of energy is removed from the skin and the blood within the skin capillaries, having a cooling effect and aiding thermoregulation. This is important in maintaining optimum conditions for enzymes. This is also true for transpiration in plants.
• What is cohesion?

  The attraction between molecules of the same type.
• What causes water's cohesion?

  Hydrogen bonds form between molecules due to the attraction between slightly positive hydrogen atoms on one molecule and the slightly negative oxygen atoms of another.
• Why is water's cohesion important to living things?

  Water molecules can form a continuous column of water, making it useful for transporting substances, e.g. in the xylem in plants. Therefore it is important in the exchange of substances for chemical reactions to support life.
• What is surface tension?

  The increased density of a liquid at the interface with air due to cohesion of molecules acting in the same direction.
• Does water have high or low surface tension and why?

  High - the top layers of water molecules do not have any water molecules above them to which they can be attracted. As a result there is a net attraction downwards.
• What does water's surface tension allow?

  Sweat droplets to form on skin (as part of thermoregulation)

  Small animals to walk on water's surface
• What is a metabolite?

  A substance that is involved in a chemical reaction as a reactant or product.
• Why is water being a metabolite important to living things?

  Water is involved in both hydrolysis reactions and condensation reactions that are essential for life.
• What is a hydrolysis reaction?

  The use of water in a chemical reaction to break down bonds in a molecule.

  e.g. digestion, break down of ATP to ADP
• What is a condensation reaction?

  Where water is released as a product during a reaction.

  e.g. protein synthesis, lipid synthesis, ATP synthesis
• What is a solvent?

  A substance capable of dissolving another substance (a solute).
• What type of substances can water dissolve and why?

  Polar substances - it too has polarity

  e.g. the slightly positive H atoms allow the water molecule to be attracted to negative charges of an ion. The ion would then become totally surrounded by water, dissolving it.
• Why is water being a solvent important to living things?

  It allows substances to move freely by dissolving them, acting as a medium for chemical reactions.

  It can transport substances around or out of the body.

  e.g. blood plasma and urine are both mainly water
• What does dipolar mean?

  Substances that have both a slightly positive and a slightly negative charge.

  e.g. water
• What is mass flow?

  The bulk movement of liquids due to pressure gradients.