3.2 Water

Question 1

Define a POLAR CHARGE

Answer 1

this is when a covalent molecule shares its electrons inequally resulting in electrons orbiting some atoms longer than others, this leads to some areas becoming slightly negative and other areas becoming slightly positively charged

Question 2

How is Water a POLAR MOLECULE

Answer 2

electrons from the H2 orbit the O atom for longer, causing the O atom to gain a small negative and the 2 H atoms to have a slight positive charge

Question 3

What are HYDROGEN BONDS?

Answer 3

these are weak bonds that form between the positive and negative regions of water molecules that are in close proximity to one another

Question 4

Characteristics of Water:

Boiling Point

Answer 4

• water has a high specific heat capacity, and so has a large boiling point, despite being lighter than both O2 and CO2.
• this is a result of the immense number of hydrogen bonds that form in water

Question 5

Characteristics of Water:

Freezing

Answer 5

• when water freezes it becomes less dense than it is as a liquid
• this is a result of the hydrogen bonds fixing the water molecules further away than if they were in a liquid, resulting in a large rigid structure which is less dense than water
• so ice floats

Question 6

Characteristics of Water:

Cohesion and Adhesion

Answer 6

• water molecules are attracted to one another and so will move as one mass - cohesion
  ie; drink through a straw
• water molecules are also attracted to other molecules and will stick to other objects - adhesion
  ie; get wet hands

Question 7

Water’s Importance in Life:

Solvent

Answer 7

• water acts as a solvent in which many solvents in an organism can dissolve in
• cytoplasm is mostly water and so water acts as a medium for chemical reactions to occur

Question 8

Water’s Importance in Life:

Transport Medium

Answer 8

• cohesion means that when water is transported molecules stick together, and adhesion means that water will stick to other polar molecules + surfaces
  this results in CAPILLARY ACTION

Question 9

Water’s Importance in Life:

Coolant

Answer 9

• water buffers temperature changes during chemical reactions in cells helping to maintain constant internal temperatures within cells
• a result of waters high SHC

Question 10

Water’s Importance in Life:

Water as a Habitat

Answer 10

• water is stable - it doesn’t change temp easily or evaporate easily
• because ice floats it forms on top of the water, forming an insulating layer keeping the water below at a constant temp allowing organisms to survive freezing conditions
• also water tension can support small insects, allowing organisms to inhabit the surface of the water too