2.2 Water

Question 1

Polarity of water

Answer 1

polar molecule
polar molecules and ions dissolve together, stick to one another
polar and non-polar molecules do not dissolve together or stick

hydrophobic: water repelling, do no dissolve in water because molecules are more attracted to each other than they are to water
hydrophilic: water attracting, stick to water molecules, ionic and polar compounds are hydrophilic and dissolve in water because molecules are more attracted to water than they are to each other

Question 2

Blood transport

Answer 2

blood transports a variety of substances , most in blood plasma, mode of transport depends on the substances solubility in water

NaCl: soluble due to polar ions - dissolved in plasma
Glucose and amino acids: polar substances - dissolved in plasma
Oxygen: non-polar - carried by red blood cells attached to haemoglobin
Cholesterol and fats: non - polar - carried by small droplets called lipoproteins

Question 3

Adhesion

Answer 3

water molecules form intermolecular associations with polar and charged molecules
this attraction to charged or polar surfaces allow water to flow in opposition of gravitational forces (capillary action)
necessary to allow water to be transported up plant stems

Question 4

Cohesion

Answer 4

water molecules stick to each other
due to hydrogen bonds that form between molecules
these bonds allow water to resist low levels of external force (surface tension)
high surface tension makes it sufficiently dense for smaller organisms to move along its surface

Question 5

Water as a Solvent

Answer 5

many substances dissolve in water due to its polarity
medium for chemical reactions
transports substances

Question 6

Thermal properties of Water

Answer 6

due to hydrogen bonding water has high mp and bp
high latent heat of vaporisation and specific heat capacity
liquid in most earth environments
remains at a relatively stable temperature
aquatic environments don’t change much
heat can be lost by evaporation hence an effective coolant

Question 7

Difference between water and methane thermal properties

Answer 7

methane is non-polar
similar molecular mass
weak intermolecular forces rather than hydrogen bonds

this causes a much lower mp and bp
a lower SHC and LH of vaporisation

Question 8

How does sweat cool us down?

Answer 8

• the change of water from a liquid to vapour requires energy
• the energy comes from the surface of your skin when it’s hot
• when sweat evaporates skin is cooled
• water has a high SHC, so it absorbs a lot of thermal energy before it evaporates
• therefore water functions as a highly effective coolant