Water

Question 1

Water molecule structure

Answer 1

1 oxygen atom covalently bonded to 2 hydrogen atoms

Question 2

What is the charges like on a water molecule?

Answer 2

Oxygen = small negative charge
Hydrogen = small positive charge

Question 3

“Polar molecule”

Answer 3

What describes water molecule because it has negative oxygen ion and positive hydrogen ion = one end slightly positive, the other slightly negative due to uneven sharing of electrons

Question 4

Hydrogen bonds

Answer 4

Formed between each water molecules because the positive hydrogen ions are attracted to oppositely charged oxygen ions

Question 5

How strong are hydrogen bonds?

Answer 5

Quite weak

Question 6

Why do hydrogen bonds effect the properties of water?

Answer 6

Because there are many even in a small volume of water

Question 7

Properties of water

Answer 7

Cohesion + adhesion
Very high specific heat capacity
Ice = less dense than liquid
High latent heat of vaporisation
Solvent
Surface tension
Metabolite
Transparent

Question 8

What happens when we heat water?

Answer 8

Energy goes to weakening the many hydrogen bonds , not changing temp
Therefore water acts as a ‘buffer’ against rapid temp changes = temp not change rapidly = its thermostable

Question 9

What’s useful about water not changing temp quickly?

Answer 9

If it did then a lot of aquatic life couldn’t survive

Question 10

Density

Answer 10

Ice is LESS DENSE than water
(Has less mass for a given volume)
So floats

Question 11

Biological role of ice

Answer 11

Acts as habitat for some organisms
Insulates the water below from freezing = organisms under ice continue living

Question 12

water’s latent heat of vaporisation

Answer 12

Amount of energy required to vaporise 1g of substance
When this is done, hydrogen bonds between water is broken = gases atoms have highest Ek
When these leave, they transfer average Ek so decrease in temp =cooling effect

Question 13

Biological role of latent heat of vaporisation

Answer 13

Allows organisms to cool without losing a lot of water eg sweating = reduces body temp
Eg in water evaporation from mesophyll cells

Question 14

Solvent

Answer 14

Many substances can dissolve in water

Question 15

Biological role of water as solvent

Answer 15

Organisms contain substances dissolved in water from metabolic reactions = so they can occur
Dissolved oxygen for aquatic life = provides habitat
Excellent transport medium due to being good solvent

Question 16

What dissolved substances does plasma have?

Answer 16

CO2, sodium ions, glucose, amino acids

Question 17

What dissolved substances travel up the xylem?

Answer 17

Magnesium ions

Question 18

Cohesion

Answer 18

Hydrogen bonding between molecules = molecules stick together
Can travel up against force of gravity ie in xylem and supports the tube

Question 19

Adhesion

Answer 19

Charge in water molecules = sticks to other materials due to charges attracting

Question 20

Surface tension

Answer 20

Hydrogen bonds allow surface of water for pond skaters to walk on = habitat

Question 21

Metabolite

Answer 21

Water is a reactant in photosynthesis + hydrolysis
And product in respiration + condensation

Question 22

What in the structure of the water molecule causes the hydrogen bonding

Answer 22

An uneven distribution of hydrogen’s electrons where they are pulled towards the oxygen atom
Forming positive cloud on the hydrogen atoms and negative cloud on the oxygen atoms