1.7 Water

• Explain how hydrogen bonds occur between water molecules?

  ● Water is polar molecule

  ● Slightly negatively charged oxygen atoms attract slightly positively charged hydrogen atoms of other water molecules
• State 5 properties of water?


  Metabolite

  Solvent

  High Specific Heat capacity

  High latent of heat vaporisation

  Strong cohesion
• Metabolite importance:

  Used in condensation / hydrolysis / photosynthesis / respiration
• Solvent (can dissolve solutes) importance

  1. Allows metabolic reactions to occur (faster in solution)
  2. 2. Allows transport of substances eg. nitrates in xylem, urea in blood
• High specific heat capacity importance:

  ● Buffers changes in temperature

  ● As can gain / lose a lot of heat / energy without changing temperature

  1. Good habitat for aquatic organisms as temperature more stable than land
  2. Helps organisms maintain a constant internal body temperature
• High latent heat of vaporisation importance

  ● Allows effective cooling via evaporation of a small volume (eg. sweat)

  ● So helps organisms maintain a constant internal body temperature
• Strong cohesion between water molecules importance:

  1. Supports columns of water eg. transpiration stream through xylem in plants

  2. Produces surface tension, supporting small organisms (to walk on water)
• 
  

  ❌- Exam insight: common mistakes ❌:(1/4)

  ❌- “Water has a high latent heat of evaporation.”

  ✅-Water has a high latent heat of vaporisation
• Exam insight: common mistakes ❌:(2/4)

  ❌- “Water is a solute.”

  ✅-Water is a solvent that dissolves other substances (solutes).
• Exam insight: common mistakes ❌:(3/4)

  ❌- “Water is cohesive which aids transpiration.”

  ✅-Transpiration is the loss of water vapour from leaves. The transpiration stream is the constant movement of water through the plant. Cohesion aids the transpiration stream.
• Exam insight: common mistakes ❌:(4/4)

  ❌- *Mixing up specific heat capacity and latent heat of vaporisation.*

  ✅-These are completely different properties - make sure you know the difference.