Water, Acids, Bases & Buffers – Key Vocabulary

These vocabulary flashcards cover the critical terms and definitions related to water’s biochemical roles, acid–base chemistry, and physiological buffer systems discussed in the lecture.

Water (H₂O)

Predominant chemical component of the body (≈50–60 % of adult weight, 75 % in children); universal solvent, heat regulator, reactant/product in metabolism, and determinant of biomolecular structure.

Solvent of Life

Role of water in dissolving and transporting polar and ionic compounds throughout blood and cellular compartments.

Dipole–Dipole Interaction

Attractive force between molecules with permanent dipoles; water’s polarity enables these interactions with solutes.

Hydrogen Bond

Weak electrostatic attraction between a hydrogen atom bound to an electronegative atom (O or N) and another electronegative atom; key to water’s high cohesion and solvent power.

Hydrophobic Effect

Tendency of non-polar regions of biomolecules to aggregate in aqueous solution, driving protein folding and membrane formation.

Heat of Fusion (Water)

Large energy removal required to convert liquid water to ice, helping prevent sudden body-temperature drops.

Heat Capacity (Water)

Amount of heat needed to raise water’s temperature; high value buffers body temperature changes.

Heat of Vaporization

Energy required to convert water to vapor; underlies cooling by perspiration and evaporation.

Thermal Conductivity (Water)

Efficiency in transferring heat, allowing dissipation from high-metabolic organs (e.g., brain) to blood and body water pool.

Nucleophile

Electron-rich species that donates an electron pair; water (lone pairs on O) acts as an excellent biological nucleophile.

Hydrolysis

Reaction in which water cleaves chemical bonds, converting polymers to monomers (e.g., protein digestion).

Dehydration (Condensation)

Reaction joining monomers and releasing water to form larger biomolecules.

Ion Product of Water (K₍w₎)

Equilibrium constant for water dissociation: [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ mol² L⁻² at 25 °C.

pH

Negative logarithm of hydrogen-ion concentration: pH = −log[H⁺]; expresses acidity/alkalinity.

pOH

Negative logarithm of hydroxide-ion concentration: pOH = −log[OH⁻]; pH + pOH = 14 at 25 °C.

Acid

Proton donor; strong acids fully dissociate (e.g., HCl), weak acids partially dissociate (e.g., acetic acid).

Base

Proton acceptor; strong bases fully dissociate (e.g., NaOH), weak bases partially dissociate (e.g., NH₃).

pKₐ

Negative log of acid dissociation constant (Kₐ); lower pKₐ signifies a stronger weak acid.

Conjugate Base

Species formed when an acid donates a proton; participates in buffer systems (e.g., HCO₃⁻ for H₂CO₃).

Monoprotic Acid

Acid that donates one proton (e.g., lactic acid).

Diprotic/Triprotic Acid

Acid able to donate two or three protons respectively (e.g., carbonic acid is diprotic, phosphoric acid triprotic).

Henderson–Hasselbalch Equation

pH = pKₐ + log([A⁻]/[HA]); relates pH to ratio of conjugate base and weak acid in a buffer.

Buffer

Solution of a weak acid/base and its conjugate that resists pH changes upon addition of strong acid or base.

Bicarbonate Buffer System

Major extracellular buffer: CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻; regulated by lungs and kidneys.

Carbonic Anhydrase

Enzyme catalyzing interconversion of CO₂ and H₂CO₃, accelerating bicarbonate buffer responses.

Hemoglobin Buffer

Intracellular (RBC) buffer using imidazole groups of histidine to bind or release H⁺, especially during CO₂ transport.

Phosphate Buffer

Intracellular and urinary buffer pair H₂PO₄⁻ / HPO₄²⁻ (pK₂ ≈ 7.2).

Protein Buffer

Buffering via ionizable side chains (e.g., carboxyl, amino, imidazole) of cellular and plasma proteins.

Acid–Base Balance

Physiological maintenance of arterial pH ≈ 7.35–7.45 via buffers, respiration, and renal excretion.

Acidosis

Condition in which blood pH drops below normal range (e.g., metabolic acidosis, respiratory acidosis).

Alkalosis

Condition in which blood pH rises above normal range (e.g., metabolic or respiratory alkalosis).

Metabolic Acidosis

Decreased pH due to excess metabolic acid or bicarbonate loss (e.g., diabetic ketoacidosis).

Respiratory Acidosis

Decreased pH from CO₂ retention owing to hypoventilation or lung disease (e.g., COPD).

Metabolic Alkalosis

Elevated pH from excess bicarbonate or acid loss (e.g., prolonged vomiting).

Respiratory Alkalosis

Elevated pH from excessive CO₂ loss, commonly due to hyperventilation.

Hyperventilation

Rapid, deep breathing that lowers arterial CO₂, predisposing to respiratory alkalosis.

Kidney Ammonium Excretion

Renal mechanism converting NH₃ to NH₄⁺ to remove acid and regenerate bicarbonate, aiding long-term pH control.

Hydrogen Ion (H⁺)

Proton whose concentration determines acidity; small changes greatly affect enzyme activity and protein structure.

Lactate

Conjugate base of lactic acid (pKₐ ≈ 3.86); accumulates during anaerobic glycolysis.

Ketone Bodies

Acetoacetic acid and β-hydroxybutyric acid—weak acids produced during fatty-acid oxidation; contribute to metabolic acidosis in excess.

Ionizable Group

Functional group (e.g., –COOH, –NH₃⁺) that can donate or accept protons; its pKₐ dictates contributions to buffering and protein charge.

Hydration Shell

Layer of water molecules surrounding ions or polar solutes, enabling their solubility and transport.

Kw Dependency on Temperature

Ion product of water increases with temperature, affecting neutral pH value.

Conformational Stability

Protein’s folded state maintained partly by hydrophobic interactions and hydrogen bonding with water.

Physiological Range

Narrow pH span (≈ 7.35–7.45) compatible with normal enzymatic and metabolic function in humans.