Chemistry, pH & Buffers

Question 1

What is the pH formula?

Accepted Answer

pH = −log[H⁺]

Question 2

What does the ion product of water K w equal at 25 °C?

Accepted Answer

K w = [H⁺][OH⁻] = 10⁻¹⁴

Question 3

Buffer capacity is maximized (pH change minimized) when which condition holds?

Accepted Answer

[acid] = [base] (i.e., pH = pKa )

Question 4

Henderson-Hasselbalch equation : pH = pKa + log ([____] / [____])

Accepted Answer

[A⁻] / [HA] ( base / acid )

Question 5

What is the normal arterial plasma [HCO₃⁻]/[CO₂] ratio , and the pH it gives?

Accepted Answer

Ratio = 20 → pH = 7.40

Question 6

What is the pKa of the bicarbonate buffer system at 37 °C?

Accepted Answer

6.1

Question 7

Which metal ion does carbonic anhydrase contain?

Accepted Answer

Zn²⁺ (zinc)

Question 8

In pure water at 25 °C, what is [H⁺] (= [OH⁻]), the neutral point ?

Accepted Answer

10⁻⁷ M (pH 7.0)

Question 9

What is the master dilution equation , and what quantity is conserved?

Accepted Answer

C₁V₁ = C₂V₂ ; moles are conserved (only volume changes)

Question 10

Cloze: Each 1-unit change in pH represents a ____-fold change in [H⁺] .

Accepted Answer

10-fold (tenfold)

Question 11

What is the conversion from pCO₂ (mmHg) to [CO₂] in mM?

Accepted Answer

[CO₂] = pCO₂ × 0.03 mM/mmHg

Question 12

What is the effective (useful) buffer range relative to pKa?

Accepted Answer

pKa ± 1 pH unit

Question 13

Two acetate buffers are equimolar — one 1.0 M, one 0.1 M. How do their pH and buffer capacity compare?

Accepted Answer

Same pH ( 4.74 ); the 1.0 M buffer has ~10× greater capacity . pH and capacity are independent .

Question 14

By what mechanism (route) is the LARGEST fraction of CO₂ transported in blood, and what percent?

Accepted Answer

As dissolved HCO₃⁻ — 78%

Question 15

What is the relationship between Ka and Kb for a conjugate acid-base pair?

Accepted Answer

Ka × Kb = Kw = 10⁻¹⁴ (so pKa + pKb = 14 )

Question 16

Is ice more or less dense than liquid water, and why?

Accepted Answer

Less dense — the hexagonal H-bond lattice holds molecules further apart

Question 17

At what temperature does water reach maximum density ?

Accepted Answer

3.98 °C (not 0 °C)

Question 18

When pH = pKa , what does the [A⁻]/[HA] ratio equal (and why)?

Accepted Answer

Ratio = 1 , because log(1) = 0

Question 19

Cloze: Acidosis = the [HCO₃⁻]/pCO₂ ratio ____ (pH < 7.35).

Accepted Answer

falls

Question 20

Cloze: Alkalosis = the [HCO₃⁻]/pCO₂ ratio ____ (pH > 7.45).

Accepted Answer

rises

Question 21

Why is the bicarbonate buffer effective at pH 7.4 despite its pKa being 6.1 (outside the ±1 range)?

Accepted Answer

Blood is an open system — the lungs continuously exhale CO₂ (the acid component), so it never accumulates

Question 22

For a STRONG acid , how does [H⁺] relate to the acid's initial concentration?

Accepted Answer

[H⁺] = initial acid concentration (dissociation is complete)

Question 23

For a WEAK acid (small α), what is the formula for [H⁺] ?

Accepted Answer

[H⁺] = √(Ka × C)

Question 24

In respiratory acidosis , what is the primary change and the renal compensation?

Accepted Answer

pCO₂ ↑ ; kidneys retain HCO₃⁻ (over days)

Question 25

In metabolic acidosis , what is the primary change and the compensation?

Accepted Answer

[HCO₃⁻] ↓ ; hyperventilation blows off CO₂ (minutes/hours)

Question 26

Which protein is the predominant buffer of the H⁺ generated when CO₂ → HCO₃⁻ inside red blood cells ?

Accepted Answer

Hemoglobin (via its histidine imidazole groups)

Question 27

What approximate kcat makes carbonic anhydrase one of the fastest enzymes known?

Accepted Answer

≈ 10⁶ s⁻¹

Question 28

Acidosis drives which electrolyte out of cells into plasma — producing what disturbance?

Accepted Answer

K⁺ shifts out → hyperkalemia

Question 29

Which noncovalent force is an entropy-driven expulsion rather than a true attraction?

Accepted Answer

The hydrophobic effect

Question 30

What is the O–H–O bond angle of the bent water molecule?

Accepted Answer

≈ 104.5°

Question 31

Why does water's high dielectric constant (80) dissolve ionic compounds?

Accepted Answer

It diminishes electrostatic attraction between ions (~80-fold vs vacuum), letting them separate and hydrate

Question 32

What is the individual energy of a single hydrogen bond ?

Accepted Answer

1–5 kcal/mol (weak alone, collectively strong)

Question 33

In a panicking patient: pH 7.49, low pCO₂, and HCO₃⁻ = 24 mM (normal) . What is the diagnosis?

Accepted Answer

Acute (uncompensated) respiratory alkalosis from hyperventilation

Question 34

Which Hb-O₂ effect couples CO₂ entry / H⁺ production in tissues to O₂ release ?

Accepted Answer

The Bohr effect (isohydric mechanism)

Question 35

What fraction of filtered HCO₃⁻ is reabsorbed by the proximal tubules , and via what enzyme?

Accepted Answer

~90% , via carbonic anhydrase -mediated H⁺ secretion

Question 36

Which urinary buffer do the distal tubules use to excrete H⁺ into urine?

Accepted Answer

Phosphate buffer ( HPO₄²⁻/H₂PO₄⁻ )

Question 37

Compare timescales: lung (respiratory) vs kidney (renal) acid-base compensation.

Accepted Answer

Lungs : minutes to hours ; kidneys : days

Question 38

Cloze: At 25 °C, pH + pOH = ____.

Accepted Answer

14

Question 39

Why is pH 7.0 NOT exactly neutral at body temperature (37 °C)?

Accepted Answer

K w is temperature-dependent and larger at 37 °C, so neutral pH is slightly below 7.0

Question 40

What is the life-compatible pH range defined in the lecture?

Accepted Answer

6.8 to 7.8

Question 41

In metabolic alkalosis , what is the primary change and a common cause?

Accepted Answer

[HCO₃⁻] ↑ ; vomiting (loss of H⁺) or hypokalemia

Question 42

What is the normal arterial pCO₂ (mmHg) and the [CO₂] it converts to?

Accepted Answer

pCO₂ = 40 mmHg → [CO₂] = 1.2 mM

Question 43

What is the normal arterial plasma [HCO₃⁻] ?

Accepted Answer

24 mM

Question 44

In a COMPENSATED acid-base disorder, what is the trap about pH vs the component values?

Accepted Answer

pH normalizes , but both [HCO₃⁻] and pCO₂ remain abnormal in absolute terms

Question 45

For mixing two solutions of the same solute, which shortcut gives volumes inversely proportional to concentration differences from the target?

Accepted Answer

The Rule of the Cross (alligation)

Question 46

A higher pKa indicates a ____ acid.

Accepted Answer

weaker

Question 47

What is the pKa of the phosphate buffer system ( HPO₄²⁻/H₂PO₄⁻ )?

Accepted Answer

≈ 6.7–7.2

Question 48

Protein buffering comes mainly from which side chain, and what is its pKa range?

Accepted Answer

Histidine side chains; pKa 5.6–7.0

Question 49

What is the buffering pKa range of N-terminal amino groups on proteins?

Accepted Answer

7.6–8.4

Question 50

Which buffer system dominates in blood PLASMA ?

Accepted Answer

The bicarbonate system

Question 51

Which buffers are the PRIMARY intracellular / red-blood-cell buffers?

Accepted Answer

Proteins (especially hemoglobin in RBCs) and phosphate

Question 52

Of the three CO₂ transport routes, what percent travels as carbamino compounds (CO₂ bound to Hb N-terminals)?

Accepted Answer

13%

Question 53

Of the three CO₂ transport routes, what percent travels as dissolved CO₂ ?

Accepted Answer

9%

Question 54

Name all three CO₂ transport routes in blood with their percentages.

Accepted Answer

78% as HCO₃⁻ , 13% as carbamino-Hb, 9% as dissolved CO₂

Question 55

What is water's high specific heat value?

Accepted Answer

4.18 kJ/g·°C

Question 56

What is water's high heat of vaporization value?

Accepted Answer

2.26 kJ/g

Question 57

WHY does water have such a high specific heat and heat of vaporization ?

Accepted Answer

Added heat must break hydrogen bonds before it can accelerate the molecules, so water absorbs much energy per degree

Question 58

For a WEAK BASE (e.g., NH₃, Kb = 1.8×10⁻⁵), what is the formula for [OH⁻] ?

Accepted Answer

[OH⁻] = √(Kb × C) , then convert to pH via pOH

Question 59

In respiratory ALKALOSIS , what is the primary change and the renal compensation?

Accepted Answer

pCO₂ ↓ (hyperventilation); kidneys excrete HCO₃⁻ (over days)

Question 60

Hyperventilation from anxiety or a panic attack causes which acid-base disorder?

Accepted Answer

Respiratory alkalosis

Question 61

How many histidine imidazole groups per hemoglobin tetramer give it its buffering power?

Accepted Answer

38 histidine imidazole groups (plus 4 N-terminal amino groups)

Question 62

Each step in the unit chain M → mM → µM → nM is multiplied by what factor?

Accepted Answer

×10⁻³ (so 1 M = 10³ mM = 10⁶ µM = 10⁹ nM)

Question 63

What density approximation does the lecture permit for dilute aqueous solutions (so 1 mL ≈ 1 g)?

Accepted Answer

Density ≈ 1 g/mL

Question 64

When mixing an acid with a base , what is the correct calculation strategy?

Accepted Answer

Account for neutralization first : compute moles of each, subtract stoichiometrically, then divide remaining moles by the total final volume