Water and its Functions

Question 1

What elements is water made up of and what charges do they have? (2)

Answer 1

• 2 hydrogens with a slight positive charge
• 1 oxygen with a slight negative charge

Question 2

What word describes the polarity of water and what is the overall charge of water? (2)

Answer 2

• Water is described to be dipolar because it has a negative (O-) and positive (H+) pole
• Although water does not have an overall charge

Question 3

How is a hydrogen bond formed? (2)

Answer 3

• It is formed when the positive pole of one water molecule is attracted to the negative pole of another water molecule
• because opposites attract

Question 4

How strong is a hydrogen bond? (2)

Answer 4

• Hydrogen bonds are weak but collectively they are strong
• and this gives water its unique properties

Question 5

Name the 7 functions of water (7)

Answer 5

• Water as a metabolite
• Water as a solvent
• Latent heat capacity of water
• Specific heat capacity of water
• Cohesion and surface tension in water
• Density and incompressibility of water
• Transparency of water

Question 6

What is a metabolite and what are the 2 metabolic reactions involving water? (3)

Answer 6

• A metabolite is a molecule that takes part in a metabolic reaction which is a chemical reaction that occurs in living organisms to keep them alive
• Condensation reaction
• Hydrolysis reaction

Question 7

Give 3 examples of water as a solvent (3)

Answer 7

• Water can dissolve gases such as CO2 and O2
• Water can dissolve waste such as ammonia and urea
• Water can dissolve enzymes whose reactions occur in water

Question 8

Describe the latent heat capacity of water and its use (5)

Answer 8

• Water has a high latent heat capacity
• because a lot of heat is needed to evaporate 1g of water
• due to hydrogen bonding
• this means that water can be used as a thermoregulatory system because water uses up a lot of heat to evaporate
• so sweating cools the body down as the water uses up body heat to evaporate it

Question 9

Describe cohesion in water and give an example (4)

Answer 9

• Cohesion is the tendency of molecules to stick together
• Water has large cohesive forces due to hydrogen bonding
• This allows water to be pulled up through a tube
• E.g. in xylem cells in a plant

Question 10

Describe surface tension in water and give an example (3)

Answer 10

• Cohesion causes surface tension when water meets the air
• The waters surface acts like a skin to support organisms on it
• E.g. pond skaters can walk on water

Question 11

Describe the specific heat capacity of water and its use (4)

Answer 11

• Specific heat capacity is the amount of energy needed to raise 1kg of water by 1C
• The specific heat capacity of water is high and it has a high boiling point
• Without hydrogen bonding water would be a gas
• The specific heat capacity acts as a buffer against sudden temperature variations

Question 12

Describe the density of water and give an example (3)

Answer 12

• Ice is less dense than water as the water molecules are further apart
• This allows ice to float and allows aquatic organisms to continue living under the water
• It can also act a layer of insulation

Question 13

Describe the compressibility of water (3)

Answer 13

• Water is very difficult to compress
• Due to the strong intermolecular forces between the water molecules
• so it provides support

Question 14

Explain why the transparency of water is useful (1)

Answer 14

• It allows light to pass through so aquatic plants can still photosynthesise as light can pass through