Lecture 3: Water

Question 1

what properties of water make it critical to life?

Answer 1

1. covalent, very stable
2. “universal” solvent
3. thermal properties
4. plays direct role in stability and behaviour of other molecules in the cell
5. plays direct role in chemical reaction mechanisms

Question 2

water forms a ___ shape due to ___ of lone pairs, it is __

Answer 2

tetrahedron; distorted tetrahedron

Question 3

it is the polar nature of water that allows it to

Answer 3

interact with other charged/polar molecules to dissolve them

Question 4

each water molecule can interact with up to __ other water molecules

Answer 4

4

Question 5

____ explains why water is a cohesive liquid at room temp

Answer 5

hydrogen bonding

Question 6

hydrogen bonds found to be less than the sum of ___

Answer 6

their van der waals radii

Question 7

hydrogen bond strength increases with

Answer 7

increase in electronegativity

Question 8

hydrogen bond formation in liquid water is a __ process. Each bond has a half life of about ____

Answer 8

dynamic; 10 pinoseconds

Question 9

most water molecules at liquid phase are bound to __ other water molecules at any given time

Answer 9

1-2

Question 10

the surface of the water is ___ molecules thick

Answer 10

one

Question 11

the surface of the water is held in tension by

Answer 11

innumerable hydrogen bonds

Question 12

why can an insect walk on the surface of the water?

Answer 12

the water molecules are more attracted to each than to the leg of the insect

Question 13

water can evaporate below the boiling point if:

Answer 13

the air around is not 100% saturated with water

Question 14

the thermal energy needed to break H bonds is taken from ___, which __

Answer 14

the liquid water, which cools it down

Question 15

solid water forms a

Answer 15

cross-linked lattice

Question 16

molecules in solid water are oriented so that ___, this provides__

Answer 16

H bonds form a straight line; maximum strength to each bond

Question 17

why is solid water less dense than liquid water?

Answer 17

the lattice causes molecules to be pushed farther apart, which lowers the density

Question 18

the transition from solid to liquid results from the breaking of __% of H bonds in ice

Answer 18

15-20

Question 19

an odd property of water is that is is __ at room temp

Answer 19

liquid

Question 20

compared to related molecules, water should have a melting point of ___ and a boiling point of __

Answer 20

-100’C and -91’C

Question 21

water separates ions by ____ interacting through ___ interactions

Answer 21

electrostatically; charge-dipole

Question 22

each ion being dissolved by water is surrounded by a __, which __

Answer 22

hydration shell of water; shields them from interacting with each other

Question 23

the ability of water to shield ion charges is measured by its ___ or __

Answer 23

dielectric constant; relative permittivity

Question 24

the dielectric constant of a solvent is a measure of its __

Answer 24

polarity

Question 25

water has a ___ dielectric constant

Answer 25

very high

Question 26

the lower the dielectric constant, the ___

Answer 26

less able it is to hydrate ions

Question 27

energy of interaction

Answer 27

the energy required to separate 2 charged particles by countering the attractive electrostatic force bewteen them

Question 28

water can dissolve other non-ionic molecules as long as they are

Answer 28

polar

Question 29

hydrophobic molecules cannot dissolve in water because

Answer 29

theyre not ionic or polar

Question 30

in the presence of hydrophobic molecule, how to water molecules react?

Answer 30

interact with each other, forming a cage around the molecule

Question 31

a clathrate represents a ___ arrangement

Answer 31

highly ordered

Question 32

a clathrate is thermodynamically ___ which causes the hydrophobic molecule ___ suddenly, reducing ___

Answer 32

unfavourable; coalesce; surface area contact to water

Question 33

clathrate coalesce suddenly is a ___ driven process

Answer 33

entropy

Question 34

the longer the HC chain the ___ soluble

Answer 34

less

Question 35

the more polar groups per carbon the __ soluble

Answer 35

more