2.1.2 - Water

Question 1

Hydrogen bonding

Answer 1

• A weak interaction between a slightly negatively charged atom(oxygen) and a slightly positively charged atom (hydrogen). - There are hydrogen bonds between water molecules

Question 2

Structure of water

Answer 2

• Water consists of 2 hydrogen atoms and 1 oxygen atom

- There is a covalent bond between the hydrogen atom and the oxygen atom

Question 3

Why is water polar?

Answer 3

• The electrons in the covalent bond are not shared equally.
• The oxygen attracts the shared electrons more strongly than the hydrogen atom
• The hydrogen atom is slightly positively charged
• The oxygen atom is slightly negatively charged

Question 4

High boiling point

Answer 4

• Water has a high BP(100 degrees Celsius)
• The multiple hydrogen bonds result in a high BP
• Water is a liquid at room temperature
• This property of water means that it can :
• > Provide habitats for aquatic organisms
• > Provide a medium for chemical reactions
• > Provide a medium for transport

Question 5

High Specific Heat Capacity

Answer 5

• Water has a high SHC, so it takes a lot of energy to increase the temperature of water
• This means that water does not heat up or cool down very easily
• High SHC means that:
• > Lakes and seas stay at a stable temperature
• > Maintaining constant temp in cells is important for enzymes to function effectively

Question 6

Cohesion & Adhesion

Answer 6

• Cohesion: Attraction between molecules of the same type
• The hydrogen bonds between molecules of water attract them to each other
• Adhesion : Water molecules attracted to other molecules
• Cohesion and adhesion result in water exhibiting capillary action : process by which water can rise up a narrow tube against the force of gravity.

Question 7

Surface Tension

Answer 7

• Surface tension causes the surface of a liquid to contract so that it occupies the least possible area
• Cohesion causes surface tension
• This property of water allows it to act as a habitat for pond-skaters

Question 8

Coolant

Answer 8

• Water cools our body down

- When the sweat evaporates, energy is transferred to the surroundings, cooling us down.

Question 9

Solvent

Answer 9

• Water is a solvent because of its polarity

- Water can easily dissolve ionic and polar molecules

Question 10

Transport medium

Answer 10

• As water is a solvent, it can be used as a transport medium for solutes

Question 11

Density

Answer 11

• Ice is less dense than water due to the hydrogen bonds formed
• As liquid water cools, more hydrogen bonds are formed.
• When it freezes to ice, the water molecules are held apart in an open lattice structure
• Ice floats on water
• This means:
• > Animals like polar bears can live on ice caps
• > Ice forms an insulating layer above the water below

Question 12

How do hydrogen bonds form between two water molecules

Answer 12

• Hydrogen bonds form between oxygen on one water molecule and hydrogen on another water molecule
• Water is polar
• Hydrogen is electropositive and oxygen is electronegative, they attract each other

Question 13

Why is the ability of water to act as a solvent important for an organism’s survival

Answer 13

• Medium for metabolic reactions because it allows ionic compounds to separate
• Transport (e.g. blood)
• A