quiz 3 study guide ]

Question 1

Why is water a liquid at room temperature?

Answer 1

Extensive hydrogen bonding between water molecules

Hydrogen bonds are responsible for many of water’s unique properties.

Question 2

What bond holds atoms together within one water molecule?

Answer 2

Covalent O–H bonds (intramolecular)

These bonds are strong and determine the molecular structure of water.

Question 3

What interaction holds water molecules together with each other?

Answer 3

Hydrogen bonds (intermolecular)

These weak interactions are crucial for the properties of water.

Question 4

Key distinction: covalent vs hydrogen bonds in water?

Answer 4

Covalent O–H bonds hold atoms within a molecule; hydrogen bonds between molecules determine physical properties

This distinction is fundamental in understanding molecular interactions.

Question 5

Why does water have a high boiling point for its size?

Answer 5

Hydrogen bonding raises boiling point (100°C at 18 g/mol)

The extensive hydrogen bonding network requires more energy to break.

Question 6

What is a hydrogen bond?

Answer 6

A weak electrostatic attraction between a donor H and an acceptor atom (O, N, or F)

Hydrogen bonds are essential in biological systems.

Question 7

Hydrogen bond donor requirement?

Answer 7

H covalently bonded to O, N, or F

This configuration allows the hydrogen to participate in hydrogen bonding.

Question 8

Hydrogen bond acceptor requirement?

Answer 8

O, N, or F with lone pairs

These atoms can stabilize the hydrogen bond through their electron pairs.

Question 9

Strength order: covalent vs H-bond vs van der Waals?

Answer 9

Covalent strongest (~100 kcal/mol) > H-bond (2–5) > van der Waals (~1)

Understanding this order is crucial for predicting molecular interactions.

Question 10

What must a molecule have to H-bond with itself?

Answer 10

Both a donor (O–H/N–H/F–H) AND an acceptor (O/N/F with lone pairs)

This requirement is key for self-association in molecules like water.

Question 11

Why are hydrogen bonds important in biology?

Answer 11

They stabilize biomolecule structure but allow flexibility

This balance is vital for the function of proteins and nucleic acids.

Question 12

Main types of noncovalent interactions in biomolecules?

Answer 12

• Hydrogen bonds
• Electrostatic interactions
• Van der Waals forces
• Hydrophobic interactions

These interactions play critical roles in the structure and function of biomolecules.

Question 13

Key difference: covalent vs noncovalent interactions?

Answer 13

Covalent = electron sharing; noncovalent = no electron sharing

This distinction is fundamental in chemistry.

Question 14

Why are weak interactions useful for life?

Answer 14

Individually weak but collectively strong; allow dynamic and reversible structure/function

This property is essential for biological processes.

Question 15

What is an acid?

Answer 15

Proton (H⁺) donor

Acids play a crucial role in chemical reactions and biological systems.

Question 16

What is a base?

Answer 16

Proton (H⁺) acceptor

Bases are essential for neutralizing acids in biological systems.

Question 17

What is the pH equation?

Answer 17

pH = −log[H⁺]

This equation is fundamental in understanding acidity and basicity.

Question 18

What does low pH mean?

Answer 18

High [H⁺] (acidic)

Low pH values indicate strong acidic conditions.

Question 19

What does high pH mean?

Answer 19

Low [H⁺] (basic)

High pH values indicate basic conditions.

Question 20

How much does [H⁺] change per 1 pH unit?

Answer 20

10-fold

This logarithmic scale is crucial for understanding acidity.

Question 21

Neutral pH at 25°C?

Answer 21

pH = 7

This is the standard reference point for acidity.

Question 22

What is a buffer?

Answer 22

A system that resists pH change when acid/base is added

Buffers are critical for maintaining stable pH in biological systems.

Question 23

What does a buffer contain?

Answer 23

• Weak acid (HA)
• Conjugate base (A⁻)

This combination allows buffers to neutralize added acids or bases.

Question 24

What does HA do in a buffer?

Answer 24

Neutralizes added base

This action helps maintain pH stability.

Question 25

What does **A⁻** do in a buffer?

Answer 25

Neutralizes added acid ## Footnote This action is essential for pH regulation.

Question 26

What determines **buffering capacity**?

Answer 26

Total concentration of buffer components ## Footnote Higher concentrations allow for greater resistance to pH changes.

Question 27

When is buffering **maximal**?

Answer 27

When [HA] = [A⁻] (pH = pKa) ## Footnote This condition provides optimal buffering ability.

Question 28

Typical effective **buffer range**?

Answer 28

pKa ± 1 pH unit ## Footnote Buffers are most effective within this range.

Question 29

Main **blood buffer systems**?

Answer 29

* Bicarbonate (~75%) * Proteins (~25%) * Phosphate (more intracellular) ## Footnote These systems are crucial for maintaining blood pH.

Question 30

Why is **bicarbonate buffer** most important in blood?

Answer 30

High [HCO₃⁻], open system (CO₂ exhaled), regulated by lungs (fast) + kidneys (slow) ## Footnote This system plays a vital role in acid-base balance.

Question 31

Bicarbonate buffer **equilibrium**?

Answer 31

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ ## Footnote This reaction illustrates the dynamic nature of the bicarbonate buffer system.

Question 32

What is meant by **“open system”** for bicarbonate buffer?

Answer 32

CO₂ can be removed by exhaling ## Footnote This property allows for rapid adjustments in pH.

Question 33

What does **hyperventilation** do to blood pH?

Answer 33

Increases pH (respiratory alkalosis) ## Footnote This condition results from excessive CO₂ removal.

Question 34

Why does **hyperventilation** raise pH?

Answer 34

Blows off CO₂ → shifts equilibrium left → decreases [H⁺] ## Footnote This shift results in a higher pH.

Question 35

What does **hypoventilation** do to blood pH?

Answer 35

Decreases pH (respiratory acidosis) ## Footnote This condition results from CO₂ retention.

Question 36

Why does **hypoventilation** lower pH?

Answer 36

Retains CO₂ → shifts equilibrium right → increases [H⁺] ## Footnote This shift results in a lower pH.

Question 37

Panic attack **hyperventilation** causes what?

Answer 37

Respiratory alkalosis (tingling/lightheadedness) ## Footnote This condition can lead to discomfort and anxiety.

Question 38

Paper bag breathing helps because…

Answer 38

Increases CO₂ intake ## Footnote This method can alleviate symptoms of hyperventilation.

Question 39

What are **colligative properties**?

Answer 39

Properties that depend on number of dissolved particles, not identity ## Footnote These properties are important in solutions and biological systems.

Question 40

What is **osmolarity**?

Answer 40

Total concentration of dissolved particles ## Footnote Osmolarity is a key factor in understanding solution behavior.

Question 41

Osmolarity **formula**?

Answer 41

Osmolarity = molarity × number of particles after dissociation ## Footnote This formula is essential for calculating osmotic pressure.

Question 42

Example: 0.25 M **Na₃PO₄** osmolarity?

Answer 42

0.25 × 4 = 1.0 osmolar ## Footnote This calculation illustrates the concept of osmolarity.

Question 43

Molarity vs **osmolarity**?

Answer 43

Molarity = concentration of molecules; osmolarity = concentration of total particles ## Footnote Understanding this difference is crucial for solution chemistry.

Question 44

Osmolarity vs **tonicity**?

Answer 44

Osmolarity counts particles; tonicity predicts cell effect (depends on membrane permeability) ## Footnote This distinction is important in biological contexts.

Question 45

Normal **blood osmolarity**?

Answer 45

~0.3 osmolar (300 mOsm) ## Footnote This value is critical for physiological function.

Question 46

Hypertonic solution does what to **cells**?

Answer 46

Cells shrink (crenation) ## Footnote This occurs due to water moving out of the cells.

Question 47

Hypotonic solution does what to **cells**?

Answer 47

Cells swell (lysis) ## Footnote This occurs due to water moving into the cells.

Question 48

Why must **IV solutions** be isotonic?

Answer 48

Prevent cell damage from water movement ## Footnote Isotonic solutions maintain cellular integrity.

Question 49

What does **amphipathic** mean?

Answer 49

Has both hydrophobic and hydrophilic regions ## Footnote This property is crucial for membrane formation.

Question 50

Amphipathic molecule **hydrophobic region**?

Answer 50

Long hydrocarbon tail (typically 8–18 carbons) ## Footnote This region is nonpolar and repels water.

Question 51

Amphipathic molecule **hydrophilic region**?

Answer 51

Polar/charged head group ## Footnote This region interacts favorably with water.

Question 52

What is a **micelle**?

Answer 52

Amphipathic molecules forming a sphere with tails inside and heads outside ## Footnote Micelles are important in solubilizing fats.

Question 53

What triggers **micelle formation**?

Answer 53

Concentration above the CMC (critical micelle concentration) ## Footnote This concentration is necessary for micelle stability.

Question 54

Why do **micelles** form in water?

Answer 54

Hydrophobic effect ## Footnote This effect drives the aggregation of nonpolar regions.

Question 55

Examples of **amphipathic molecules**?

Answer 55

* Fatty acids/soaps * Detergents (SDS) * Bile salts ## Footnote These molecules play critical roles in biological processes.

Question 56

Biological importance of **amphipathic molecules**?

Answer 56

* Membrane formation * Detergent solubilization * Bile salt fat emulsification ## Footnote These functions are essential for digestion and cellular structure.

Question 57

What is the **hydrophobic effect**?

Answer 57

Nonpolar molecules aggregate in water because water entropy increases ## Footnote This effect is fundamental in biological systems.

Question 58

Is the **hydrophobic effect** due to attraction between nonpolar molecules?

Answer 58

No—it's driven by increased entropy of released water ## Footnote This understanding is crucial for molecular interactions.

Question 59

Why do **nonpolar molecules** “cluster” in water?

Answer 59

Aggregation releases ordered water “cages,” increasing entropy ## Footnote This clustering is a key aspect of the hydrophobic effect.

Question 60

What happens to **ΔG** when hydrophobic groups aggregate?

Answer 60

ΔG becomes negative (favorable) ## Footnote This indicates that the process is thermodynamically favorable.

Question 61

Hydrophobic effect is mainly **entropy-driven** or **enthalpy-driven**?

Answer 61

Entropy-driven ## Footnote This characteristic is essential for understanding molecular behavior.

Question 62

Biological roles of **hydrophobic effect**?

Answer 62

* Protein folding * Membrane bilayers * Protein binding * Enzyme-substrate binding * Drug-receptor binding ## Footnote These roles are critical for biological function.

Question 63

Water **autoionization reaction** (simple form)?

Answer 63

H₂O ⇌ H⁺ + OH⁻ ## Footnote This reaction is fundamental to acid-base chemistry.

Question 64

More accurate **autoionization reaction**?

Answer 64

2 H₂O ⇌ H₃O⁺ + OH⁻ ## Footnote This representation emphasizes the role of hydronium ions.

Question 65

What is **Kw**?

Answer 65

Kw = [H⁺][OH⁻] ## Footnote This product is constant at a given temperature.

Question 66

Kw value at **25°C**?

Answer 66

1.0 × 10⁻¹⁴ ## Footnote This value is crucial for calculating pH and pOH.

Question 67

[H⁺] and [OH⁻] in **pure water at 25°C**?

Answer 67

Both 1.0 × 10⁻⁷ M ## Footnote This equality defines neutral conditions.

Question 68

What is **pOH**?

Answer 68

pOH = −log[OH⁻] ## Footnote This measure is related to pH and acidity.

Question 69

Relationship between **pH and pOH** at 25°C?

Answer 69

pH + pOH = 14 ## Footnote This relationship is fundamental in acid-base chemistry.

Question 70

In any aqueous solution, what stays constant at **25°C**?

Answer 70

[H⁺][OH⁻] = 1.0 × 10⁻¹⁴ ## Footnote This constant is essential for understanding solution behavior.

Question 71

Neutral means what?

Answer 71

[H⁺] = [OH⁻] ## Footnote This condition defines neutrality in solutions.

Question 72

Why isn’t **neutral** always pH 7?

Answer 72

Kw changes with temperature ## Footnote This variation affects the definition of neutrality.

Question 73

Neutral pH at **37°C** (body temp) is about…

Answer 73

~6.8 (because Kw is higher) ## Footnote This adjustment is important for physiological processes.

Question 74

What is **Ka**?

Answer 74

Acid dissociation constant: Ka = [H⁺][A⁻]/[HA] ## Footnote This constant quantifies the strength of an acid.

Question 75

What is **pKa**?

Answer 75

pKa = −log(Ka) ## Footnote This measure is used to express acid strength.

Question 76

Low **pKa** means…

Answer 76

Stronger acid (donates H⁺ easily) ## Footnote This relationship is crucial for understanding acid behavior.

Question 77

High **pKa** means…

Answer 77

Weaker acid (reluctant to donate H⁺) ## Footnote This indicates a lower tendency to ionize.

Question 78

Henderson–Hasselbalch **equation**?

Answer 78

pH = pKa + log([A⁻]/[HA]) ## Footnote This equation is essential for buffer calculations.

Question 79

When pH = pKa, what is the ratio **[A⁻]/[HA]**?

Answer 79

1 (equal concentrations) ## Footnote This condition indicates optimal buffering.

Question 80

When pH > pKa, which form predominates?

Answer 80

A⁻ (deprotonated, conjugate base) ## Footnote This shift is important for understanding acid-base behavior.

Question 81

When pH < pKa, which form predominates?

Answer 81

HA (protonated, conjugate acid) ## Footnote This condition indicates a higher concentration of the acid form.

Question 82

Buffer **selection rule**?

Answer 82

Choose buffer with pKa within ±1 of desired pH ## Footnote This guideline ensures effective buffering.

Question 83

Rule of thumb: 2 pH units below **pKa** means…

Answer 83

~99% HA (protonated) ## Footnote This rule helps predict acid-base behavior.

Question 84

Rule of thumb: 2 pH units above **pKa** means…

Answer 84

~99% A⁻ (deprotonated) ## Footnote This rule is useful for understanding buffer systems.

Question 85

Histidine side chain **pKa** is about…

Answer 85

~6.0 (imidazole) ## Footnote This property is important for enzyme function.

Question 86

Why is **histidine** important in enzymes?

Answer 86

Can donate/accept protons near physiological pH ## Footnote This flexibility is crucial for catalytic activity.

Question 87

Phosphate buffer **pKa** (given) and where important?

Answer 87

pKa = 6.8; important intracellularly ## Footnote This buffer system plays a key role in cellular processes.

Question 88

Bicarbonate buffer **pKa** and blood ratio at pH 7.4?

Answer 88

pKa = 6.1; [HCO₃⁻]/[H₂CO₃] ≈ 20:1 ## Footnote This ratio is vital for maintaining blood pH.

Question 89

Common mistake: **pKa vs pH**?

Answer 89

pKa is property of an acid; pH is property of a solution ## Footnote This distinction is essential for understanding acid-base chemistry.

Question 90

Can you use **Henderson–Hasselbalch** for strong acids?

Answer 90

No—only valid for weak acids/buffers ## Footnote Strong acids do not establish a stable equilibrium.

Question 91

Why can log([A⁻]/[HA]) be **negative**?

Answer 91

When [A⁻] < [HA] (pH < pKa) ## Footnote This situation indicates a predominance of the protonated form.

Question 92

Do all **buffers** work at all pH values?

Answer 92

No—must be within pKa ± 1 ## Footnote This limitation is crucial for effective buffering.