water

Question 1

what are polar molecules

Answer 1

molecules which have regions of negativity and regions of positivity.
- negative electrons are not always shared equally by the atoms of different elements in covalent bonds
- electrons may spend more time closer to one atom than the other
- atom with the greater share of electrons will be slightly negative (d-) compared to the other atom which is slightly positive (d+)

Question 2

polarity of OH bonds

Answer 2

• oxygen has a greater share of electrons in an O-H bond
• oxygen is d-
• hydrogen is d+

Question 3

hydrogen bonds

Answer 3

• polar molecules interact with each other as the positive and negative regions attract each other and form bonds called hydrogen bonds
• they are relatively weak interactions
• break and reform between the constantly moving water molecules
• they occur in high numbers

Question 4

water has an unusually high boiling point. explain

Answer 4

• small molecule, lighter than gases CO2 and O2, but is a liquid at room temperature
• due to hydrogen bonding
• takes a lot of energy to increase the temperature of water and for it to become gaseous

Question 5

when water freezes it turns to less dense ice, but most substances are more dense in their solid state. explain.

Answer 5

• because of hydrogen bonding
• as water is cooled below 4C, hydrogen bonds fix the positions of the polar molecules slightly further apart than the average distance in the liquid state
• produces giant, rigid but open structure
• every oxygen atom at the centre of a tetrahedral arrangement of hydrogen atoms
• so its less dense

Question 6

water has cohesive properties

Answer 6

• moves as one mass because molecules are attracted to each other (cohesion)
• so plants are able to draw up water from roots
• water has adhesive properties which means that water molecules are attracted to other materials
• water molecules are more cohesive to each other than they are to air which results in water having surface tension

Question 7

water acts as a solvent

Answer 7

• many solutes in an organism can dissolve in it
• cytosol in prokaryotes and eukaryotes is mainly water
• water acts as a medium for chemical reactions and also helps transport dissolved compounds into and out of cells

Question 8

water makes a very efficient transport medium in living things

Answer 8

-cohesion between water molecules means molecules will stick together when water is transported through the body
- adhesion occurs between water molecules and other polar molecules and surfaces
- adhesion and cohesion results in capillary action(the process by which water can rise up a narrow tube against the force of gravity

Question 9

water acts as a coolant

Answer 9

• helps buffer temperature changes during chemical reactions in prokaryotic/eukaryotic cells
• this is because of the large amounts of energy required to overcome hydrogen bonding
• maintaining constant temperatures in cellular environments is important as enzymes only work in a narrow temperature range

Question 10

many organisms live in water

Answer 10

• water is stable
• does not change temperature or become a gas easily, providing a constant environment
• ice floats so it forms on the surface, not the bottom which forms an insulating layer
• aquatic organisms would not be able to survive freezing temps if their habitat froze solid
• some small organisms inhabit the surface of water as surface tension is strong enough to support them