2.2 water

Question 1

water molecules are polar and there are hydrogen bonds between them but like why lol

Answer 1

• 8 protons in the oxygen atom, while there is only 1 proton in each of the hydrogen atom
• oxygen with more protons attract the electrons more strongly, hence the oxygen end of a water molecule is a little more negative while the hydrogen end is a little more positive
• slightly positive charged regions of the hydrogen atoms of a water molecule is attracted to the slightly negative region of the oxygen atom of an adjacent water molecule
• attraction results in the formation of a hydrogen bond between the water molecules
• hydrogen atoms are transitionary in nature, and these bonds are constantly breaking and reforming between different water molecules

Question 2

what are the 4 emergent properties of water that contributes to the ability to sustain life on earth?

Answer 2

• cohesion between water molecules (cohesive)
• ability to adhere to surfaces (adhesive)
• ability to moderate temperature (thermal)
• versatility as a solvent (solvent)

Question 3

how does hydrogen bonding and dipolarity explain the cohesive property of water?

Answer 3

• water molecules are attracted to each other via hydrogen bonds, there is a level of cohesiveness between water molecules, and water molecules and also water droplets have a tendency to stick to each other
• even though hydrogen bonds are generally considered weak, each water molecule can form 4 hydrogen bonds with other water molecules, and the sheer number of gives water its strong cohesive abilities
• examples:
  • water on vertical surfaces tend to congregate into droplets due to the cohesive forces between water molecules
  • surface tension arising from cohesive forces in water allows for insects to stand on the surface of a body of water

Question 4

how does hydrogen bonding and dipolarity explain the adhesive properties of water?

Answer 4

• forces of attraction can also form between water molecules and charged or polar substances
• forces are weak individually, but the large number of bonds give the adhesion greater strength
• allows water to defy gravity and stick onto surfaces
• an important trait of water that allows water to move up the xylem vessels in plants via capillary action

Question 5

how does hydrogen bonding and dipolarity explain the thermal properties of water?

Answer 5

• high heat capacity compared to comparable liquids
• when heat is applied to a liquid in general, the molecules within tend to vibrate more and move further apart, leading to an increase in temperature
• however, when heat is applied to water, the hydrogen bonds between adjacent water molecules resist the moving apart of molecules, and hence more heat energy is required to raise the temperature of water as compared to other liquids of the same mass
• thus water is considered to have high thermal inertia
• due to the high heat capacity of water, water can be used as a good insulator, and also as a good store for heat energy
• can absorb or release a large amount of energy with small changes in its temperature
• amount of energy required to raise 1g of water by 1 degree Celsius is 4.2J
• 4.2J is also considered to be the value of one calorie

Question 6

how does hydrogen bonding and dipolarity explain the solvent properties of water?

Answer 6

• can allow a wide variety of organic and inorganic molecules to dissolve in it, with the main examples being polar or charged molecules
• some polar molecules dissolve as water molecules can form hydrogen bonds with them
• some ionic compounds are also soluble as water
• molecules can surround the positive and negative ion in the compound and separate them into individual ions, allowing them to dissolve
• water molecules around these ions form a shell called a hydration shell

Question 7

what is hydrophilic?

Answer 7

• substances that can dissolve in water are considered to be hydrophilic
• substances that water can adhere to are also considered to be hydrophilic, like cellulose

Question 8

what is hydrophobic?

Answer 8

• molecules insoluble in water are considered hydrophobic
• usually, molecules are hydrophobic if they are non-polar, or do not possess any charges
• cannot form hydrogen bonds or attract polar water molecules
• lipids are hydrophobic
• hydrophobic substances can dissolve in other solvents like organic solvents

Question 9

how are glucose and amino acids transported in blood? (with relation to their solubility in water)

Answer 9

• blood mainly made up of water (90% to 95%)
• glucose is a polar molecule and can form hydrogen bonds with water allowing it to dissolve and be carried in blood
• amino acids can dissociate in water to form charged ions, allowing them to dissolve in water in blood

Question 10

how is oxygen transported in blood? (with relation to its solubility in water)

Answer 10

• small, non-polar molecule
• due to its small size, it is mildly soluble in water
• amount of oxygen carried in blood in the form of dissolved oxygen is not able to support human life due to high demands of oxygen by cells in the body
• to transport oxygen, specialised cells known as red blood cells, which are rich in haemoglobin, are used to transport oxygen

Question 11

how are cholesterol and fats transported in blood? (with relation to their solubility in water)

Answer 11

• non-polar substances that are not soluble in water
• carried in blood with the help of lipoproteins present
• form complexes known as lipoprotein complexes with lipoproteins, and these complexes are soluble in water

Question 12

how is sodium chloride transported in blood? (with relation to its solubility in water)

Answer 12

• can dissociate in water to form ions, stabilised by the hydration shells around them

Question 13

compare the thermal properties of water with that of methane.

Answer 13

methane:

• chemical formula of CH4
• common waste product of prokaryotes living in anaerobic conditions
• nonpolar
• density = 0.46 g / cm3
• specific heat capacity = 2.2 J g-1 degrees celsius-1
• latent heat of vapourisation = 760 J g-1
• melting point = – 182 degrees celsius
• boiling point = – 160 degrees celsius

water:
- polar
- density = 1 g / cm3
- specific heat capacity = 4.2 J g-1 degrees celsius-1
- latent heat of vapourisation = 2257 J g-1
- melting point = 0 degrees celsius
- boiling point = 100 degrees celsius

Question 14

how does water work as a coolant in sweat?

Answer 14

• high temp impact the efficiency of enzyme based reactions, and may even denature proteins and enzymes necessary in life
• water has a high latent heat of vapourisation, it takes a lot of energy to convert water into the gaseous state via evaporation
• sweat is effective as a coolant, as when water evaporates, it removes a large amount of heat energy from the body