2.2.2 properties of water

Question 1

how many properties of water are there & list them

Answer 1

1. liquid
2. density
3. solvent
4. cohesion & surface tension
5. high specific heat capacity
6. high latent heat of vaporisation
7. reactant

Question 2

(1. liquid) water is liquid at room temperature, so it can:

Answer 2

• provide habitats for living things (rivers, lakes & seas)
• form major component of tissues in living organisms
• provide reaction medium for chemical reactions
• provide effective transport medium (eg. blood, vascular tissue)

Question 3

(2. density) because ice is less dense than water, it can:

Answer 3

• provide aquatic organisms with a stable environment to live in during the winter
• ponds/other bodies of water are insulated against extreme cold –> ice layer reduces rate of heat loss

Question 4

why is ice less dense than water?

Answer 4

• water becomes more dense when it gets colder until about 4 degrees
• (due to its polar nature) the water molecules align themselves in a structure less dense than liquid water

Question 5

(3. solvent) as water is a good solvent, it can:

Answer 5

• allow molecules/ions to move around & react together in water –> many reactions occur in cytoplasm (70% water)
• allow molecules/ions to be transported around living things whilst dissolved in water

Question 6

how is water a good solvent?

Answer 6

• as water is polar, the positive/negative parts are attracted the positive/negative parts of the solute
• the water molecules cluster around these solute molecules/ions & help to separate them/keep them apart
• they dissolve & solutions formed

Question 7

name of examples of water being a good solute

Answer 7

• ionic solutes eg. sodium chloride
• covalent solutes eg. glucose

Question 8

(4. surface tension/cohesion) due to this:

Answer 8

• columns of water in plant vascular tissue are pulled up xylem from roots
• insects (eg. pond skaters) can walk on water

Question 9

explain surface tension/cohesion

Answer 9

• water molecules on surface are hydrogen-bonded to molecules beneath (& more attracted than air molecules above)
• surface of water contracts (molecules pulled inwards)
• gives surface of water ability to resist force applied

Question 10

(5. high specific heat capacity) why is it important?

Answer 10

• living things (incl prokaryotes/eukaryotes) need stable temp. for enzyme-controlled reactions to occur properly
• aquatic organisms need stable environment to live in

Question 11

what is water temperature a measure of

Answer 11

kinetic energy of water molecules

Question 12

what is the specific heat capacity

Answer 12

the amount of heat energy required to raise 1kg of water by 1 degrees
–> 4.2 KJ

Question 13

(6. high latent heat of vaporisation) it can:

Answer 13

• cool living things
• ^keep temperatures stable

Question 14

explain what the term ‘high latent heat of vaporisation’ means

Answer 14

when water evaporates, it helps (the heat energy) the molecules break apart from each other to become a gas

Question 15

(7. reactant) examples of reactions water is included in:

Answer 15

• eg. photosynthesis
• hydrolysis reactions eg. digestion of starch, proteins & lipids

Question 16

what reactions is water’s role as a reactant extremely important for

Answer 16

digestion & synthesis of large biological molecules