water & inorganic ions

• structure of a water molecule

  dipolar molecule 

  hydrogen bonding
• dipolar molecule

  -electrons in covalent bonding are not shared equally 

  -the oxygen has a greater electronegativity meaning it has a greater pull on the electrons 

  -oxygen has a slightly negative charge and hydrogen has a slightly positive charge
• hydrogen bonding

  -positive pole (hydrogen) of one water molecule is attracted to the negative pole (oxygen) of another water molecule

  -the attractive force between opposite charges is a hydrogen bond

  -hydrogen bonds are relatively weak but many together become strong
• properties of water

  metabolite

  cohesion

  adhesion

  surface tension

  density 

  high latent heat of vaporisation

  high specific heat capacity 

  solvent

  transparent
• density

  -water most dense at 4°c

  -when water freezes the hydrogen bonds between the water form a rigid lattice

  -the molecules in ice spread out in a lattice so it expands and is less dense so it floats

  -forms an insulating layer in aquatic environments which acts as a barrier to the cold

  -the water below doesn't freeze so organisms can still move and swim to survive
• metabolite

  -water takes place in many metabolic reactions

  -it is the medium in which enzyme-catalysed reactions take place 

  -water is used in hydrolysis and formed in condensation reactions

  -water is required in photosynthesis and respiration
• solvent

  -universal solvent

  -metabolic reactions occur faster in solution

  -solvent due to its dipolar nature

  -ionic compounds made from a negatively charged atom and positively charged atom so attracted to postive and negative atoms in water 

  -mineral ions dissolved in water can be taken up by plants
• cohesion

  -the attraction of water molecules of the same type

  -water molecules 'stick' to eachother as they are polar and have hydrogen bonds 

  -water molecules stick to eachother in the transpiration stream to transport water
• adhesion

  -the attraction of water molecules to a different type of molecule or object 

  -sticking to the side of a measuring cylinder
• surface tension

  -how hard it is to break the surface of a liquid

  -at an interface between air and water, the water molecules on the surface forms hydrogen bonds with water molecules below it but not above it

  -the unequal distribution of bonds causes the water surface to contract and form a tough film
• transparent

  -allows aquatic organisms to respire and live

  -photosynthesis can occur within the water
• high latent heat of vaporisation

  -the heat energy it takes to change the substances state

  -lots of energy required to break the hydrogen bonds so it is hard to evaporate

  -sweating is effective for cooling the body as sweat for sweat glands gains energy to evaporate
• high specific heat capacity

  -the heat energy it takes to change the temperature of 1kg by 1°c

  -has lots of hydrogen bonds that require a lot of energy to break

  -water can gain or lose a lot of energy without changing temperature
• inorganic ions

  H+

  Na+

  Ca2+

  Fe2+

  PO43-
• H+

  hydrogen ions 

  more H+ ions means something is more acidic
• Na+

  sodium ions

  co-transport of glucose and amino acids
• Ca2+

  calcium ions

  muscle contraction

  helps insulin be released from the pancreas

  transmitting nerve impulses

  co-factors for various enzymes
• Fe2+

  iron ions 

  component of haemoglobin which binds to oxygen

  red blood cells
• PO43-

  phosphate ions 

  components of DNA and ATP