water (a)

Question 1

how does hydrogen bonding occur between water molecules?

Answer 1

In an O-H bond, oxygen has a greater share of the electrons than hydrogen. This makes oxygen slightly negative, and hydrogen slightly positive. since water has 2 hydroxyl groups, it is polar.

Question 2

what are hydrogen bonds?

Answer 2

relatively weak interactions, which break and reform between the constantly moving water molecules.

Question 3

how do polar molecules interact with each other?

Answer 3

the positive and negative regions of the molecule attract each other and form hydrogen bonds.

Question 4

why has water got unique properties?

Answer 4

because hydrogen bonds occur in high numbers and give water unique characteristics.

Question 5

characteristics of water

Answer 5

• high boiling point
• small, lighter than gases like CO2 or O2
• liquid at room temp.
• freezes into ice
• has cohesive properties
• has adhesive properties

Question 6

why does it have a relatively high boiling point?

Answer 6

due to hydrogen bonding between water molecules - takes a lot of energy to increase the temp. of water to make it evaporate

Question 7

why is ice less dense than water?

Answer 7

below 4 degrees C, the hydrogen bonds fix positions of the polar molecules slightly further apart than the average distance in the liquid state. this produces a giant, rigid but open structure with every O atom at the centre of a tetrahedral arrangement of hydrogen atoms, resulting in solid ice that is less dense than liquid water.

Question 8

what is cohesion?

Answer 8

water moves as one mass because the molecules are attracted to each other

Question 9

what is adhesion?

Answer 9

water is attracted to other materials

Question 10

why does water have a ‘skin’ of surface tension?

Answer 10

because water molecules are more strongly cohesive to each other than they are to air.

Question 11

what are the roles of water?

Answer 11

• a solvent
• transport medium
• coolant
• habitat

Question 12

water as a solvent

Answer 12

• since it is a polar molecule, it acts as a solvent in which many of the solutes in an organism can be dissolved.
• the cytosol of prokaryotes and eukaryotes is mainly water
• dissolved compounds easily transported

Question 13

water as a transport medium

Answer 13

• efficient transport medium within living things
• effects of cohesion and adhesion result in water exhibiting capillary action - the process by which water can rise up a narrow tube against the force of gravity

Question 14

water as a coolant

Answer 14

• helps buffer temp. changes during chemical reactions in prokaryotic + eukaryotic cells because of the large amounts of energy required to overcome hydrogen bonding
• important in cellular environments since enzymes are only active in a narrow temp. range

Question 15

water as a habitat

Answer 15

• it is stable + does not easily change temp. so it provides a constant environment
• since ice floats it forms on surfaces, acting as an insulating layer above the water - sustains aquatic organisms habitats
• surface tension is strong enough to support small insects that inhibit the surface of water, e.g. pond skaters