Lecture 3: Water

Question 1

linear
sequence of the nucleotide residues in a strand of DNA is maintained
by _____ bonds (covalent or ionic

Answer 1

covalent

Question 2

the double helix structure of DNA is stabilized by ___

interactions between different parts of the molecule

Answer 2

noncovalent

Question 3

every
kind of protein is made up of amino acids linked by ___
bonds

Answer 3

covalent peptide

Question 4

Why is water unique?

Answer 4

the strong tendency of water molecules to form hydrogen bonds with other water molecules

Question 5

what are the roles of the 6 electons in the outer orbital of oxygen atom in water?

Answer 5

two are involved in covalent bonds to the hydrogen atoms.

The other four electrons exist in nonbonded pairs, which are excellent hydrogen-bond acceptors.

Question 6

vaporization of water

requires __ amount of energy for a molecule of its size

Answer 6

large

Question 7

true or false: Only the boiling point not the heat of vaporization of water are therefore remarkably high

Answer 7

false: Both the heat of vaporization

and the boiling point

Question 8

What is heat capacity?

Answer 8

Heat capacity is a measure of

the energy that must be added to raise (or removed to lower) the temperature of a substance by 1 °C

Question 9

Ice is a molecular lattice
formed by indefinite repetition of a
___ pattern.

Answer 9

tetrahedral hydrogen-bonding

Question 10

Why is ice’s density is low?

Answer 10

Because of the length of the hydrogen
bonds, the structure is a relatively
open one, which accounts for the low
density of ice.

Question 11

Each molecule in a tetrahedral lattice in ice is hydrogen-bonded to how many other molecule?

Answer 11

four

Question 12

The structure of liquid water has been described as ____ of hydrogen bonds

Answer 12

“flickering clusters”

Question 13

Why is the liquid phase of water more dense than the solid phase of water?

Answer 13

the liquid phase of water is more
dense than its solid phase because when the lattice breaks down,
molecules can move closer together.

Question 14

Does water have high viscosity? What is viscosity?

Answer 14

Yes; it is the resistance to flow

Question 15

Does water have high surface tension? What is surface tension?

Answer 15

Yes, it is the resistance of a liquid surface to distortion or penetration).

Question 16

Does water have high dielectric constant? What is it effect/what does it do?

Answer 16

Yes. It lowers electrostatic interaction between cations and anions.

Question 17

Water is a good solvent because

Answer 17

its tendency to
form hydrogen bonds and
its polar character.

Question 18

What are hydrophilics?

Answer 18

water-loving

Question 19

Is water is an excellent solvent for

ionic compounds?

Answer 19

Yes

Question 20

Explain how water dissolves salt

Answer 20

The interactions of the negative ends of the water dipoles with cations and the positive ends of water dipoles with anions
in aqueous solution cause the ions to become hydrated, that is, surrounded
by shells of oriented water molecules called hydration shells

Question 21

What are hydrophobics?

Answer 21

water-fearing

Question 22

Hydrophilic forms ___, while hydrophobic forms ___ in water

Answer 22

hydration shell, clathrate

Question 23

Clathrate formation corresponds to ____, which is unfavorable in nature

Answer 23

decrease in entropy or randomness of mixture

Question 24

Explain what the hydrophobic effect is

Answer 24

Surrounding
two hydrophobic molecules with two separate cages requires
more ordering of water in clathrates than surrounding both
hydrophobes within a single cage. Thus, the hydrophobic molecules
tend to aggregate, because doing so releases some water molecules
from the clathrates, thereby increasing the entropy of the solvent.

Question 25

What are amphipathic molecules?

Answer 25

they have both hydrophobic and hydrophilic properties

Question 26

Amphipatic have ___- head and ____ tail

Answer 26

hydrophilic; hydrophobic