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*Straight A Student* Biology OCR A A-level Notes
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[Surface tension -
water
molecules due hydrogen to
bonds creating surface tension
Practical for detergent and water
Surface tension is the force which helps a blob of water on a surface hold its shape and not spread
out. The surfactant molecules of the detergent break apart these forces and make water behave,
well, wetter!
Practical for water and capillary tube .
Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and
result in a meniscus which turns upward. The surface tension acts to hold the surface intact. Capillary
action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid
molecules.
Practical for ice cube and water
The polar molecules form a crystal structure at 4oC so water expands
Practical for expanding ice
There is a strong tendency to form a network of hydrogen bonds, where each hydrogen atom is in a line
between two oxygen atoms. This hydrogen bonding tendency gets stronger as the temperature gets lower
(because there is less thermal energy to shake the hydrogen bonds out of position). The ice structure is
completely hydrogen bonded, and these bonds force the crystalline structure
water structure ← formed by the
•
water has covalent bonds attraction of
•
Polar molecule because of the uneven distribution of charge .
the H+ ( poshegion)
•
r molecule and a
)
small in size
•
forms hydrogen bonds at cool temperatures ( below 4
"
) negative region
weak ( often 2)
-
0 of
bonds
←
electronegative
.
another .
( is stronger so
oxygen
pulls the electrons to its side)
← electro positive
different to other
bonded
hydrogen
molecules . .
.
( page 5)
,%!%j
HIGH COHESION
Water is unusual tendency together due to
-
. . . of molecules to stick hydrogen
I:[ III. III water molecules on the surface are pulled inwards
Bonding between molecules other water molecules due to hydrogen bonds tension and
to
creating surface
-
allowing organisms such as pond skaters to move .
Roles, Properties and Explaination
liquid provides habitats
•
at room temperature so .
Hydrogen bonds hold them together stronger .
•
low viscosity so can flow easily
-
effective transport medium provide ,
a reaction medium
component of tissues and dissolves ionic and polar solutes because it's a polar m .
controlled
•
stable temperature for enzyme reactions and . aquatic organisms .
Has a high shc because Its bonds
cause water molecules to be held together quite tightly lots of energy to increase their kinetic
energy
.
.
latent heat of vaporisation Na bonding between H20 molecules it alot of heat to
•
means takes
-
evaporate water .
Effective cooling mechanism .
•
Universal solvent -
solvent for ionic solids and for substances with polar groups .
molecules and ions can move around and react together .
molecules can be transported whilst
dissolved in water eg to remove area .
•
metabolism -
water is a raw material for photosynthesis Hydrolysis
. reactions break
down many complex molecules .
many chemical reactions take place in solution .
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