OSAT Chemistry cheat sheet

Atomic structure: Z = protons = electrons in a neutral atom; mass number A = protons + neutrons; isotopes differ only in neutron count and share chemical behavior but differ in mass.

Electron configuration follows Aufbau (1s 2s 2p 3s 3p 4s 3d 4p), Pauli exclusion (two electrons per orbital, opposite spins), and Hund's rule (maximize unpaired spins within a subshell).

Periodic trends: atomic radius decreases left-to-right and increases top-to-bottom; ionization energy and electronegativity increase left-to-right and decrease down a group; metallic character follows the reverse of ionization energy.

Mole relationships: n = m/M, N = n x 6.022e23, molarity M = mol solute / L solution; molar mass from formula sums atomic masses.

Stoichiometry decision rule: balance the equation first, convert given quantity to moles, apply the mole ratio from coefficients, then convert to requested units; identify the limiting reactant by comparing mole ratios.

Gas laws: PV = nRT with R = 0.08206 L atm/mol K; combined gas law P1V1/T1 = P2V2/T2; STP molar volume 22.4 L/mol at 0 C and 1 atm.

Solutions: dilution M1V1 = M2V2; colligative properties depend on particle count (van't Hoff factor i) not identity; strong electrolytes dissociate completely, weak partially.

Acid-base and equilibrium: pH = -log[H3O+], pOH = 14 - pH at 25 C, Kw = 1.0e-14; Ka x Kb = Kw for a conjugate pair; Le Chatelier shifts away from added stress.

Thermochemistry and kinetics: q = mc(delta T); delta H negative = exothermic; delta G = delta H - T delta S; spontaneous when delta G < 0; rate depends on concentration, temperature, surface area, and catalysts.

Safety hierarchy: goggles and apron for all wet labs; fume hood for volatile or toxic vapors; never pipette by mouth; add acid to water, not water to acid, when diluting.

Waste rules: halogenated and non-halogenated organic waste kept separate; heavy-metal solutions never poured down the drain; broken glass goes in a designated sharps/glass container, not regular trash.

Significant figures: multiplication and division keep the least number of sig figs; addition and subtraction keep the least number of decimal places; exact counting numbers are unlimited.

Measurement error: accuracy is closeness to the true value, precision is reproducibility; random error scatters both ways, systematic error shifts all readings in one direction.

Lab technique: read volumetric glassware at the bottom of the meniscus; rinse burettes with titrant; use a primary standard (e.g., KHP) to standardize NaOH.

Separation methods: filtration removes insoluble solids; distillation separates by boiling point; chromatography by differential affinity; extraction by differing solubility in two immiscible phases.

Spectroscopy basics: flame tests identify metal cations by emission color; Beer-Lambert law A = epsilon b c relates absorbance linearly to concentration; atomic emission lines are quantized.

Graphing and data: slope of a linear calibration gives the constant; extrapolate cautiously; report units; R-squared near 1 indicates good linear fit but not necessarily accuracy.

Scientific reasoning: a hypothesis must be falsifiable; a control isolates the independent variable; correlation does not establish causation; peer review and replication establish consensus.