Lecture 1 (water)

• Why is water polar?

  Oxygen atom is more electronegative than the hydrogen atoms so attracts electrons more. Gives oxygen slight negative charge & hydrogens slight positive charge.
• How are strong interactions made between water molecules?

  Weak bonds form between oxygen of one molecule and hydrogen of another. Weak bonds add up to make strong interactions (hydrogen bonding)
• Describe the hydrogen bonding in liquid water:


  Bonds constantly made & broken
• Describe the hydrogen bonding in ice:


  Bonds are fixed. Ice less dense than water so floats.
• Why is surface ice helpful?


  Insulates water & keeps it liquid, otherwise most water on Earth would be frozen.
• Why does water have a high bp & mp compared to molecules of same size?


  Hydrogen bonding. Water is liquid at 0-100.C so life can exist at temperatures on Earth.
• What do hydrophilic molecules contain?

  Polar covalent bonds. The electronegative atoms can form hydrogen bonds.
• Why do polar molecules have high solubility?


  Can make hydrogen bonds with the water & therefore dissolve in it.
• Why are hydrophobic molecules insoluble in water?


  No electronegative atoms (e.g, benzene) so can't form hydrogen bonds with water & don't mix well with it (e.g, oil in water).
• What is the hydrophobic effect?


  Hydrophobic molecules tend to stick together in solution- minimises unfavourable interactions with water. Important in forming correct structure of biological membranes & proteins.
• Why do ions dissolve in water?


  Form electrostatic interactions between ions & polar water.
• What are electrolytes?


  Ions dissolved in the water in the body.
• What are phosphate (PO4(3-) & carbonate (CO3(2-) ions important for?

  Maintaining correct pH
• What can electrolyte imbalance cause?


  Severe illness or death
• Hyponatremia:


  Salt conc. too low
• Hypernatremia:


  Salt conc. too high (usually due to dehydration)
• What is osmolarity?


  Concentration of electrolytes (ions)
• Why may osmolarity be different from molarity?


  Salts dissociate into individual ions when they dissolve.
• What is molarity?


  Concentration of molecules dissolved in water (mol/L)
• What is the total osmolarity of 1M Nacl?


  2 Osmolar (osm/L). (1M Na+ + 1M Cl-)
• What is formed when water dissociates?

  Hydronium ion and hydroxyl ion.
• Where is Na+ low?


  inside cells
• Where is Na+ high?


  Outside cells
• Where is K+ high?


  inside cells
• Where is K+ low?


  Outside cells
• Where is Ca 2+ high?


  inside endoplasmic reticulum
• Where is Ca 2+ very low?


  in cytosol of cells
• What does a hydrogen bond look like?


  :

  
• What does hydrogen bonding look like in water?


  :

  
• What does hydrogen bonding look like in ice?


  :

  
• Example of dissociation/ionisation?


  Water dissociation (loss of H+)
• Solubility:


  Ability to be dissolved (in water)