Chapter 2

Question 1

. In contrast, nonpolar biomolecules are poorly

soluble in water because

Answer 1

they interfere with water-water

interactions but are unable to form water-solute interactions.

Question 2

Hydrogen bonds

account for the relatively high melting point of water, because

Answer 2

much thermal energy is required to break a sufficient proportion
of hydrogen bonds to destabilize the crystal lattice of ice.

Question 3

why are hydrogen bonds highly directional

Answer 3

see pg 262

Question 4

Water dissolves salts such as NaCl by

Answer 4

y hydrating and stabilizing the
Na
\+
and Cl
−
ions, weakening the electrostatic interactions
between them and thus counteracting their tendency to associate
in a crystalline lattice

Question 5

what else does water readily dissolve and give examples

Answer 5

Water also readily dissolves
charged biomolecules, including compounds with functional
groups such as ionized carboxylic acids (—COO
−
), protonated
amines (—NH
+
3
), and phosphate esters or anhydrides. Water
replaces the solute-solute hydrogen bonds linking these
biomolecules to each other with solute-water hydrogen bonds,
thus screening the electrostatic interactions between solute
molecules.

Question 6

Nonpolar compounds such

as benzene and hexane are hydrophobic meaning

Answer 6

they are unable to
undergo energetically favorable interactions with water
molecules, and they interfere with the hydrogen bonding among
water molecules.

Question 7

When two uncharged atoms are brought very close together,

Answer 7

their
surrounding electron clouds influence each other. Random
variations in the positions of the electrons around one nucleus
may create a transient electric dipole, which induces a transient,
opposite electric dipole in the nearby atom. T

Question 8

. The two dipoles

weakly attract each other,

Answer 8

bringing the two nuclei closer. These
weak attractions are called van der Waals interactions (also
known as London dispersion forces). As the two nuclei draw
closer together, their electron clouds begin to repel each other

Question 9

when are the nuclei said to be in van der waals contact

Answer 9

At

the point where the net attraction is maximal,

Question 10

Macromolecules such as proteins, DNA, and RNA contain so many

Answer 10

sites of potential hydrogen bonding or ionic, van der Waals, or
hydrophobic clustering that the cumulative effect can be
enormous.

Question 11

what is te most stable structure for macromolecules

Answer 11

For macromolecules, the most stable (that is,
the native) structure is usually that in which these weak
interactions are maximized. ( weak interactions being examples of vdw, hydrophobic clustering- its in card 10)

Question 12

what is essential to the function for many proteins

Answer 12

For many proteins, tightly bound water molecules are

essential to their function.

Question 13

osmotic pressure graph on pg 281

Answer 13

kk

Question 14

explanation of the vant hoff equation on pgs 281-282

Answer 14

kk

Question 15

good practice question on pg 285

Answer 15

kk

Question 16

good summary on pg 286

Answer 16

kk

Question 17

The very different electronegativities of H and O make water a

Answer 17

highly polar molecule, capable of forming hydrogen bonds with
itself and with solutes. Hydrogen bonds are fleeting, primarily
electrostatic, and weaker than covalent bonds.

Question 18

Alcohols, aldehydes, ketones, and compounds containing N—H

bonds all form

Answer 18

hydrogen bonds with water and are therefore

water soluble

Question 19

By screening the electrical charges of ions and by increasing
the entropy of the system, water

Answer 19

dissolves crystals of ionizable

solutes.

Question 20

N2, O2, and CO2 are… nh3 and h2s are…

Answer 20

nonpolar and poorly soluble in water…ionizable and therefore very water soluble.

Question 21

Nonpolar (hydrophobic) compounds- how they dissolve, what can’t they do and what does their presence cause. what do they do to avoid water

Answer 21

dissolve poorly in water;
they cannot hydrogen-bond with the solvent, and their presence
forces an energetically unfavorable ordering of water molecules
at their hydrophobic surfaces. To minimize the surface exposed to
water, nonpolar and amphipathic compounds such as lipids form
aggregates (micelles and bilayer vesicles) in which the
hydrophobic moieties are sequestered in the interior, an
association driven by the hydrophobic effect, and only the more
polar moieties interact with water.

Question 22

van der Waals interactions exist when

Answer 22

two nearby nuclei
induce dipoles in each other. The nearest approach of two atoms
defines the van der Waals radius of each.

Question 23

Weak, noncovalent interactions, in large numbers, decisively

influence

Answer 23

the folding of macromolecules such as proteins and

nucleic acids.

Question 24

(related to card 23, they were part of the same point)The most stable macromolecular conformations
are those in

Answer 24

which hydrogen bonding is maximized within the
molecule and between the molecule and the solvent, and in which
hydrophobic moieties cluster in the interior of the molecule away
from the aqueous solvent.

Question 25

When two aqueous compartments are separated by a semipermeable membrane (such as the plasma membrane separating a cell from its surroundings), water moves across that membrane to

Answer 25

o equalize the osmolarity in the two compartments.

Question 26

(part of the same point as card 25) what produces osmotic pressure

Answer 26

When two aqueous compartments are separated by a semipermeable membrane (such as the plasma membrane separating a cell from its surroundings), water moves across that membrane to equalize the osmolarity in the two compartments. This tendency for water to move across a semipermeable membrane produces the osmotic pressure

Question 27

When weak acids are dissolved in water, | they contribute

Answer 27

H + by ionizing; weak bases consume H + by becoming protonated.

Question 28

The ionization of water can be measured by its electrical | conductivity;

Answer 28

``` pure water carries electrical current as H3O + migrates toward the cathode and OH − migrates toward the anode. ```

Question 29

ph chart on pg 298

Answer 29

kk

Question 30

why is Measurement of pH is one of the most important and | frequently used procedures in biochemistry.

Answer 30

``` The pH affects the structure and activity of biological macromolecules, so a small change in pH can cause a large change in the structure and function of a protein ```

Question 31

acids and bases def

Answer 31

Acids (in the Brønsted-Lowry definition) are proton donors, and bases are proton acceptors

Question 32

When a proton donor such as acetic | acid (CH3COOH) loses a proton... also what is a conjugate acid-base pair

Answer 32

it becomes the corresponding proton acceptor, in this case the acetate anion (CH3COO − ). A proton donor and its corresponding proton acceptor make up a conjugate acid-base pair (Fig. 2-15), related by the reversible reaction equation at the bottom of pg 302

Question 33

what is a titration curve and what does it reveal

Answer 33

in this example on pg 306, a titration curve is a plot of pH against the amount of NAOH added. a titration curve reveals the pka of the weak acid./

Question 34

see the example on pg 307-30-8

Answer 34

kk

Question 35

Pure water ionizes slightly, forming

Answer 35

equal numbers of hydrogen ions (hydronium ions, H3O + ) and hydroxide ions.

Question 36

The extent of ionization is described by an equilibrium constant, Keq = {H}{OH}/[h20), from which the ion product of water, Kw, is derived.

Answer 36

``` At 25 °C, Kw = [H + ] [OH − ] = (55.5 M)(Keq) = 10^ −14 M 2 ```

Question 37

The pH of an aqueous solution reflects, on a logarithmic scale,

Answer 37

the concentration of hydrogen ions:

Question 38

Weak acids partially ionize to release a hydrogen ion, thus... also what do weak bases do and what is the extent of these processes characteristic of?

Answer 38

lowering the pH of the aqueous solution. Weak bases accept a hydrogen ion, increasing the pH. The extent of these processes is characteristic of each particular weak acid or base and is expressed as an acid dissociation constant:

Question 39

acid dissoc constant

Answer 39

keq= [H+]{A-]/[HA]= Ka

Question 40

pka expresses

Answer 40

on a logarithmic scale, the relative strength | of a weak acid or base: the equation is ]pka= log 1/[Ka]= -log Ka

Question 41

The stronger the acid,/base... also how do u find the pka on a titration curve

Answer 41

the smaller its pKa; the stronger the base, the larger the pKa of its conjugate acid. The pKa can be determined experimentally; it is the pH at the midpoint of the titration curve.

Question 42

buffer

Answer 42

``` are aqueous systems that tend to resist changes in pH when small amounts of acid (H + ) or base (OH − ) are added. ```

Question 43

buffering region

Answer 43

Notice that the titration curve of acetic acid has a relatively flat zone extending about 1 pH unit on either side of its midpoint pH of 4.76. In this zone, a given amount of H + or OH − added to the system has much less effect on pH than the same amount added outside the zone. This relatively flat zone is the buffering region of the acetic acid–acetate buffer pair. At the midpoint of the buffering region, where the concentration of the proton donor (acetic acid) exactly equals that of the proton acceptor (acetate), the buffering power of the system is maximal; that is, its pH changes least on addition of H + or OH − .

Question 44

what is the henderson hasselbach equation useful for

Answer 44

This equation is simply a useful way of 316 restating the expression for the ionization constant of an acid.

Question 45

henderson hasslebach fits

Answer 45

the titration curve of all weak acids and enables us to deduce some important quantitative relationships. For example, it shows why the pKa of a weak acid is equal to the pH of the solution at the midpoint of its titration.

Question 46

henderson hasslebach

Answer 46

The shape of the titration curve of any weak acid is described by the Henderson-Hasselbalch equation, which is important for understanding buffer action and acid-base balance in the blood and tissues of vertebrate

Question 47

. So, an amount of NaOH that increases the pH of | water from 7 to 12 increases

Answer 47

the pH of a buffered solution, as in | (b), from 7.0 to just 7.2. Such is the power of buffering!

Question 48

The pH of a bicarbonate buffer system depends on

Answer 48

``` the concentrations of H2CO3 and HCO − 3 , the proton donor and acceptor components. The concentration of H2CO3 in turn depends on the concentration of dissolved CO2, which in turn depends on the concentration of CO2 in the gas phase, or the partial pressure of CO2, denoted pCO2 . Thus, the pH of a bicarbonate buffer exposed to a gas phase is ultimately determined by the concentration of HCO − 3 in the aqueous phase and by pCO2 in the gas phase. ```

Question 49

acidosis and alkalosis- pgs 330-332

Answer 49

kk

Question 50

A mixture of a weak acid (or base) and its salt resists

Answer 50

``` changes in pH caused by the addition of H + or OH − . The mixture thus functions as a buffer. ```

Question 51

The pH of a solution of a weak acid (or base) and its salt is given by

Answer 51

the Henderson-Hasselbalch equation:

Question 52

In cells and tissues, phosphate and bicarbonate buffer systems maintain

Answer 52

intracellular and extracellular fluids near pH 7.4. | Enzymes generally work optimally near this physiological pH.

Question 53

Medical conditions such as untreated diabetes that lower the | pH of blood, causing

Answer 53

acidosis, or raise it, causing alkalosis, can be | life-threatening.

Question 54

whats something that could cause alkalosis

Answer 54

hyperventilation - see somewhere around pg 330 ish i think