Tuesday, 7 August 2012

stpm biology chapter 1 water note

Water
Dipolar molecules
-uneven charge within the molecules
  oxygen (slight -ve charge), hydrogen(slight +ve charge)
-bond angle 104.5°
-hydrogen bond between positively charged oxygen & negatively charge hydrogen in liq. state 
  form, break and reform ( high frequency)

Universal solvent
-caused by polarity of water
  • a suitable solvent for ions and polar molecules.
  •  displace their attraction to each other.
~polar dissolve in water = hydrophilic 
~nonpolar [lipid and hydrocarbon] = hydrophobic

Density
 In liq. state, water molecules 
  • break and reform
  • are arranged more irregular but closer
In ice (solid) state, water molecules
  • are arranged regularly, hexagonal crystalline lattice
  • Each can form a max. no. of  4 hydrogen bond with other water molecules
Advantage of lattice structure of ice
-occupies more space
-has less water molecules per vol.
therefore water expands when it freezes, less dense than liq. water

*Water has max. density at 4°C
-at 0° and below ice floats on surface>>form insulating layer
-prevent water fr. freezing in lower depths
therefore aquatic organisms like fish can survive during winter

 or u can download this one.... BIOLOGY-STPM-LOWER-6-CHAPTER-1




1 comment:

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