2: Water

Question 1

most abundant compound in organisms (70% of body weight)

Answer 1

water

Question 2

molecular geometry of water

Answer 2

bent or V-shaped (nearly tetrahedral arrangement of four electron groups around O)

Question 3

how many hydrogen bonds can each water molecule make?

Answer 3

4 (2 on oxygen, 1 on each hydrogen)

Question 4

8 unique properties of water that sustain life on Earth

Answer 4

high cohesion
high adhesion
high surface tension
high specific heat
high heat of vaporization
liquid at room temperature
excellent solvent
hydrophobic exclusion

Question 5

act of sticking together

Answer 5

cohesion

Question 6

act of sticking to something (due to ability of water to form H bonds)

Answer 6

adhesion

Question 7

what component of plant cell walls can form H bonds with water molecules, allowing the latter’s transport?

Answer 7

cellulose (the hydroxyl groups)

Question 8

measure of the resistance of a substance to increase its surface area due to high cohesion of its molecules

Answer 8

surface tension

Question 9

2 types of molecules in a sample of water

Answer 9

inner and surface

Question 10

explain the high surface tension in water

Answer 10

there is formation of stronger bond between surface water molecules as they are pulled inward by a net inward force due to absence of attractive force acting from above and thus preventing them from being stretched or broken

Question 11

2 importance of high surface tension of water

Answer 11

• allows denser things and animals to float
• formation of water droplets

Question 12

amount of heat per unit mass required to raise the temperature by 1degree Celsius

Answer 12

specific heat

Question 13

specific heat of water

Answer 13

2 cal/g-degree Celsius

Question 14

what happens when temperature of water increases? decreases?

Answer 14

increase in T: water molecules would move faster due to increase in kinetic energy, leading to the breaking of H bonds which absorbs heat

decrease in T: water molecules would move slower due to decrease in KE, causing the formation of H bonds which releases heat

Question 15

2 importance of moderation of temperature by water

Answer 15

regulate air temperature change near oceans

regulation of internal body temperature

Question 16

process at which as liquid evaporates, the liquid surface that remains behind cools down

Answer 16

evaporative cooling

Question 17

what makes evaporative cooling possible

Answer 17

high heat of vaporization of water

Question 18

amount of heat needed to turn 1 g of liquid into a vapor without a rise in temperature of the liquid

Answer 18

heat of vaporization

Question 19

heat of vaporization of water

Answer 19

540 cal/g at 25 degrees Celsius (high due to hydrogen bonding)

Question 20

2 importance of evaporative cooling

Answer 20

sweating

evaporation of water on the surface of leaves

Question 21

how many hydrogen bonds does water molecules form on ice? on liquid water?

Answer 21

ice: 4 H bonds, stable

liquid water: 3.2 H bonds on average, constant breaking and reformation of H bonds

Question 22

ice is ____ than water

Answer 22

less dense

Question 23

why does water readily dissolve other polar compounds and salts?

Answer 23

high dielectric constant

Question 24

measure of the ability of a solvent to keep opposite charges apart

Answer 24

dielectric constant

Question 25

refers to when ions are nonrandomly surrounded by water molecules that attenuates the coulombic forces between these ions

Answer 25

hydration

Question 26

tendency of amphiphiles to self-associate in water than to dissolve individually

Answer 26

hydrophobic effect

Question 27

why do amphiphile molecules cluster together instead of each amphiphile molecule being surrounded by water molecules?

Answer 27

the latter is not favored because of the resulting highly ordered structure (decrease in entropy of the system) and the former also requires fewer water molecules

Question 28

spherical amphiphilic structures that have a hydrophobic core and a hydrophilic shell

Answer 28

micelles

Question 29

3 instances of water as medium for biochemical processes

Answer 29

weak interactions in the aqueous system

water and its ionization products (H3O+ and OH-)

weak acid-base equilibria/physiological buffers

Question 30

4 weak interactions of water in aqueous systems that are individually weak but are collectively significant

Answer 30

hydrogen bonding
ionic interactions
hydrophobic interactions
van der Waals forces

Question 31

4 examples where H bonds are found in biological systems

Answer 31

between alcohol and water
between carbonyl ketone and water
between peptide groups
between nitrogenous bases

Question 32

bond between nucleic acids

Answer 32

phosphodiester bond