"Are protons just hydrogen ions?"
Kana asked in the night laboratory.
Rei nodded. "H⁺. But doesn't exist alone."
"Why?"
"Naked protons are unstable. Immediately bind to water molecules."
Milia drew a diagram. "H₃O⁺. Hydronium ion."
"This is acid?"
"Acids are substances that release protons," Rei explained.
Toma added. "Bases accept protons."
"Simple," Kana said.
"But profound," Milia smiled. "Acid-base reactions are journeys of protons."
Rei prepared a beaker. "Dissolving acetic acid in water."
"What happens?"
"CH₃COOH → CH₃COO⁻ + H⁺. Proton leaves."
Kana questioned. "All leave?"
"No, only some. Reaches equilibrium."
"Equilibrium?"
"Dissociation and recombination happen at same rate," Milia explained.
Rei continued. "This equilibrium constant is pKa."
"pKa?"
"Index of acid strength. Smaller means stronger acid."
Toma brought a pH meter. "Let's measure."
Immersing in liquid, numbers displayed.
"pH 4.7," Kana read.
"Logarithm of proton concentration," Rei explained. "pH = -log[H⁺]."
"Why logarithm?"
"Concentration range is too wide. From 10⁻¹⁴ to 1."
Milia supplemented. "With logarithmic scale, easier to handle."
"pH 7 is neutral?"
"Yes. When [H⁺] = [OH⁻]."
Rei made another solution. "Mixing acetic acid and sodium acetate."
"What for?"
"Buffer solution. Stabilizes pH."
Kana looked curious. "Stabilize?"
Milia explained. "Adding acid or base, pH barely changes."
"Why?"
"Equilibrium adjusts," Rei drew a diagram.
"When acid is added?"
"Acetate ion accepts protons, becomes acetic acid."
"When base is added?"
"Acetic acid releases protons, becomes acetate ion."
Toma experimented. "One drop of hydrochloric acid... pH doesn't change!"
"That's buffering," Milia said.
Kana questioned. "In living organisms too?"
"Absolutely necessary," Rei emphasized. "Blood pH is kept at 7.4."
"Why important?"
"Enzyme activity depends on pH. Small changes lose function."
Milia supplemented. "Blood has carbonic acid/bicarbonate buffer system."
"How does it work?"
"CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻," Rei wrote the equation.
"Complex..."
"But maintains pH between 7.35 and 7.45."
Toma was impressed. "Range of 0.1?"
"Beyond that threatens life."
Kana said quietly. "Proton journeys support life."
"Yes," Milia nodded. "Every second, countless protons move."
Rei continued. "Stomach is pH 2. Small intestine is pH 8. Different for each organ."
"Why?"
"Different functions. Stomach acid needed for digestion. Small intestine has pH suitable for absorption."
Kana questioned. "How fast do protons move?"
"Very fast," Milia answered. "Transmitted through hydrogen bond networks."
"Grotthuss mechanism," Rei explained. "Protons jump."
"Jump?"
"Relayed from water molecule to water molecule."
Toma drew a diagram. "Like bucket relay."
"Correct. That's why it's faster than diffusion."
Kana stared at the beaker. "Right now, protons are traveling inside."
"Billions, trillions of journeys," Milia said.
Rei said quietly. "Most chemical reactions involve proton transfer."
"That important?"
"Enzyme reactions, respiration, photosynthesis... all involve protons."
Kana was moved. "Tiny protons move the world."
Milia smiled. "Proton journeys are chemistry's poetry."
The three imagined invisible proton flows in the night laboratory.
Through water, through proteins, across membranes.
Protons continue their journey.
For life.