"Cold."
Kana spilled acetone on her hand.
Rei panicked. "Wipe it off. High volatility."
"Volatility?"
"Evaporates easily," Milia explained. "When vaporizing, it takes heat away."
Kana looked at her hand. "That's why it's cold."
"Endothermic process," Rei wrote in his notebook. "Liquid to gas phase transition."
Milia supplemented. "For molecules to leave the liquid, intermolecular forces must be broken."
"That energy is taken from surroundings."
Kana asked. "What is acetone?"
"A type of ketone," Rei answered. "Organic compound with a carbonyl group."
"Carbonyl group?"
Milia drew a structural formula. "C=O. Double bond between carbon and oxygen."
"This group determines ketone properties."
Kana stared. "Two lines for equals?"
"Double bond. σ bond and π bond," Rei explained.
"Strong bond, but polar."
Milia continued. "Oxygen has higher electronegativity. Attracts electrons."
"So C=O is a polar bond."
Kana wrote in her notebook. "Polarity = charge distribution."
"Accurate," Rei acknowledged.
"So ketones dissolve in water?" Milia asked.
Kana thought. "Since they're polar... they dissolve?"
"Partially correct," Rei said. "Acetone dissolves in water."
"But larger ketones are less soluble."
"Why?"
Milia explained. "Balance of the whole molecule. Ratio of hydrophobic to hydrophilic parts."
"Carbonyl group is hydrophilic. But hydrocarbon chain is hydrophobic."
Rei drew a diagram. "In small molecules, carbonyl influence is large."
"In large molecules, hydrocarbon part dominates."
Kana understood. "It's about balance."
"Molecular properties are determined by both functional groups and skeleton."
Toma entered the room. "What are you talking about?"
"Ketones," Kana answered.
"Ah, acetone. Nail polish remover smell."
Milia nodded. "Used to dissolve nail polish."
"High dissolving power," Rei supplemented. "Can dissolve both polar and nonpolar substances."
Kana was interested. "It's a convenient solvent."
"Commonly used in laboratories."
Toma brought up another topic. "Are ketones also made in the body?"
Milia became serious. "Ketone bodies. Increase during fasting or diabetes."
"Used as energy source."
Rei explained. "When glucose is insufficient, ketone bodies are synthesized from fatty acids."
"Acetoacetic acid, β-hydroxybutyric acid, acetone."
Kana was surprised. "Acetone, inside the body too?"
"Small amounts are normal. But excess is dangerous."
"Ketoacidosis," Milia warned. "Blood becomes acidic."
Toma understood. "That's why diabetic patients are careful."
Rei summarized. "Chemical substances change meaning with context."
"Solvent in the lab. Metabolic product in the body."
Kana looked at the acetone bottle. "Same molecule, different roles in different places."
Milia added. "Concentration is also important. Can be poison or medicine."
Toma asked. "What's the difference between ketones and aldehydes?"
Rei answered. "Position of the carbonyl group."
"Ketones in the middle of the molecule. Aldehydes at the end."
Milia compared structures. "R-CO-R' is ketone, R-CHO is aldehyde."
"This difference affects reactivity."
Kana proposed an experiment. "I want to confirm the difference."
"Silver mirror reaction," Rei suggested. "Aldehydes react, but ketones don't."
They added reagents to test tubes.
In the aldehyde tube, mirror-like silver precipitated.
"Amazing."
No change in the ketone tube.
"The position of functional groups makes such a difference."
Milia smiled. "The beauty of organic chemistry."
"Small differences create big distinctions."
Outside the window, wind blew. The pale coldness of ketones taught them about the molecular world.