Chemistry
Core concepts
Chemistry supports biochemistry and physiology. Know atomic structure, electron configuration, periodic trends, ionic and covalent bonding, polarity, hydrogen bonding, and intermolecular forces. Acid-base chemistry is essential: pH equals negative log of hydrogen ion concentration, buffers resist pH change, and the Henderson-Hasselbalch equation relates pH, pKa, and the ratio of conjugate base to acid. Organic chemistry questions test functional groups, isomerism, stereochemistry, and reaction types. Understand carbohydrates, lipids, proteins, and nucleic acids at the level of monomers, bonds, and major functions. Thermodynamics and kinetics distinguish spontaneity from reaction rate.
Traps
pH is logarithmic: a change of one pH unit means a tenfold change in hydrogen ion concentration. Acid strength is not the same as concentration; a dilute strong acid can have a higher pH than a concentrated weak acid. Do not confuse enantiomers, which are nonsuperimposable mirror images, with diastereomers. In buffers, maximum capacity occurs near the pKa.
Worked example and rule of thumb
For 0.01 M HCl, assuming complete dissociation, hydrogen ion concentration is 0.01 M, or 10^-2 M, so pH is 2. For 0.01 M acetic acid, pH is higher than 2 because the weak acid only partly dissociates. Rule: each pH unit is a tenfold hydrogen ion change.
Exam focus
Practice pH and buffer calculations, functional-group recognition, and bonding polarity. These predict solubility, reactivity, and biological behavior.