Ch 2 Water

Question 1

What percentage of the mass of living things is water?

Answer 1

60 - 70%

This indicates the essential role of water in biological systems.

Question 2

How is body water distributed in cells?

Answer 2

2/3 inside cells, 1/3 outside cells

Question 3

What is the primary role of water in biological systems?

Answer 3

Water is the solvent for biological systems.

Question 4

What is a hydrophilic compound?

Answer 4

A water-loving compound that interacts with and dissolves in water.

Question 5

What types of compounds are considered hydrophilic?

Answer 5

• Polar compounds
• Ionic compounds

Question 6

What is a hydrophobic compound?

Answer 6

A water-hating compound that avoids water.

Question 7

What types of compounds are considered hydrophobic?

Answer 7

• Non-polar compounds
• Oils and fats

Question 8

What makes water a polar molecule?

Answer 8

Electrons are unequally shared between oxygen and hydrogen.

Question 9

Define electronegativity.

Answer 9

The tendency of an atom to attract electrons.

Question 10

What is the significance of hydrogen bonds in biochemistry?

Answer 10

They provide organization to macromolecules but are weak enough to be readily broken.

Question 11

What is a hydrogen bond?

Answer 11

A dipole-dipole bond between an electronegative atom and a hydrogen atom.

Question 12

True or False: Water can act as both a weak acid and a weak base.

Answer 12

True

Question 13

What is the relationship between [H+] and [OH–] in a solution?

Answer 13

[H+] and [OH–] are inversely related.

Question 14

What is the pH of pure water at 25°C?

Answer 14

7.0

Question 15

What does a strong acid do in solution?

Answer 15

Completely ionizes in aqueous solution.

Question 16

What does a weak acid do in solution?

Answer 16

Is incompletely ionized in aqueous solution.

Question 17

Define pK.

Answer 17

A measure related to an acid’s tendency to ionize.

Question 18

What is the ionization constant of water (Kw)?

Answer 18

Kw = [H+][OH–] = 10–14 at 25°C.

Question 19

What is the pH scale?

Answer 19

A logarithmic scale that measures hydrogen ion concentration.

Question 20

What is the significance of pH being a logarithmic scale?

Answer 20

A difference of one pH unit represents a tenfold difference in [H+].

Question 21

What is the formula for calculating pH?

Answer 21

pH = -log[H+]

Question 22

What does the term ‘amphipathic’ refer to?

Answer 22

Molecules that have both hydrophilic and hydrophobic regions.

Question 23

What is the Henderson-Hasselbalch equation used for?

Answer 23

Calculating pH based on the concentrations of an acid and its conjugate base.

Question 24

What happens to ionic compounds when they dissolve in water?

Answer 24

They are pulled apart due to ion-dipole interactions.

Question 25

Fill in the blank: Water can donate or accept a _______.

Answer 25

proton

Question 26

What is the physiological pH of human blood?

Answer 26

7.4

Question 27

What is the relationship between the concentration of H+ and OH– in neutral water?

Answer 27

[H+] = [OH–] = 10–7 M

Question 28

What does the acid dissociation constant (Ka) measure?

Answer 28

The strength of an acid in terms of its ionization in water.

Question 29

How does the electronegativity of oxygen compare to carbon and hydrogen?

Answer 29

Oxygen is more electronegative than both carbon and hydrogen.

Question 30

What effect does adding an acid have on the pH of a solution?

Answer 30

Decreases pH

Question 31

What effect does adding a base have on the pH of a solution?

Answer 31

Increases pH

Question 32

What is the definition of an acid in biochemistry?

Answer 32

A substance that can donate a proton

Question 33

What is the definition of a base in biochemistry?

Answer 33

A substance that can accept a proton

Question 34

What does K_a represent?

Answer 34

The acid dissociation constant

Question 35

What is the relationship between K_a and acid strength?

Answer 35

The larger the K_a value, the stronger the acid

Question 36

How is pK_a calculated?

Answer 36

pK_a = -log K_a

Question 37

What does a lower pK_a value indicate?

Answer 37

A stronger acid

Question 38

What is the pK_a of an acid with a K_a value of 3.3 x 10^-3?

Answer 38

2.5

Question 39

How does adding an acid affect pH?

Answer 39

Increases [H+] and decreases pH

Question 40

How does adding a base affect pH?

Answer 40

Decreases [H+] and increases pH

Question 41

What is a buffer?

Answer 41

A weak acid whose pH resists change upon addition of either more acid or more base

Question 42

What components make up a buffer?

Answer 42

A weak acid and its conjugate base

Question 43

What is the principal buffer in cells?

Answer 43

H2PO4-/HPO4^2-

Question 44

What is the Henderson-Hasselbalch equation used for?

Answer 44

To relate pH to pK_a and the concentrations of acid and conjugate base

Question 45

When is a buffer's maximum buffering capacity achieved?

Answer 45

When pK_a equals pH, and [HA] = [A-]

Question 46

What happens to the pH if [A-] is higher than [HA]?

Answer 46

The pH is higher than the pK_a

Question 47

What happens to the pH if [A-] is lower than [HA]?

Answer 47

The pH is lower than the pK_a

Question 48

What is the effective buffer range?

Answer 48

About 1 pH unit above or below the pK_a

Question 49

What ratio of HA to A- occurs 1 pH unit below the pK_a?

Answer 49

90% HA: 10% A-

Question 50

What ratio of HA to A- occurs 1 pH unit above the pK_a?

Answer 50

10% HA: 90% A-

Question 51

What is the bicarbonate buffer system's role in blood?

Answer 51

It helps maintain blood pH

Question 52

What effect does hyperventilation have on blood pH?

Answer 52

Increases blood pH

Question 53

What effect does hypoventilation have on blood pH?

Answer 53

Decreases blood pH

Question 54

What is carbonic acid's pK_a value?

Answer 54

Around 6.36

Question 55

What is the significance of carbonic anhydrase?

Answer 55

One of the fastest enzymes, catalyzing reactions at rates of 10^4 to 10^6 reactions per second

Question 56

Fill in the blank: Buffers resist changes in pH by either _______ H+ when an acid is added, or _______ H+ when a base is added.

Answer 56

[binding] [releasing]