Chemistry content domain (weight not stated in source)
Domain 1: Chemistry content domain (weight not stated in source)
The CSET Science Chemistry domain samples the chemistry a candidate must command to teach secondary science: atomic structure and periodicity, bonding and intermolecular forces, stoichiometry and solution chemistry, thermochemistry, kinetics, equilibrium, acid–base behavior, redox and electrochemistry, and selected organic, nuclear, and laboratory-safety ideas. Questions reward correct chemical reasoning and unit-aware calculation, not memorized trivia.
Core rules
- Electron configurations follow the Aufbau order, Pauli exclusion, and Hund’s rule; Cr and Cu are standard exceptions ([Ar]3d⁵4s¹ and [Ar]3d¹⁰4s¹). Across a period, atomic radius decreases and first ionization energy generally increases; down a group the reverse occurs.
- Use VSEPR to assign shapes and bond angles, then decide molecular polarity from vector cancellation. Stronger intermolecular forces-ion–dipole, hydrogen bonding, dipole–dipole, London dispersion-raise boiling point and solubility in like solvents.
- Stoichiometry is mole-ratio reasoning. Convert mass or solution volume to moles, identify the limiting reagent, then convert product moles to mass or concentration. For solutions, M = mol/L and dilution uses M₁V₁ = M₂V₂.
Worked example
25.0 mL of 0.200 M AgNO₃ is mixed with 25.0 mL of 0.150 M NaCl. Find the limiting reagent, mass of AgCl formed, and [Ag⁺] remaining.
Ag⁺ + Cl⁻ → AgCl(s). Moles Ag⁺ = 0.0250 L × 0.200 mol/L = 5.00 × 10⁻³ mol. Moles Cl⁻ = 0.0250 L × 0.150 mol/L = 3.75 × 10⁻³ mol. The 1:1 ratio makes Cl⁻ limiting. AgCl mass = 3.75 × 10⁻³ mol × 143.32 g/mol = 0.537 g. Excess Ag⁺ = (5.00 − 3.75) × 10⁻³ = 1.25 × 10⁻³ mol; total volume = 0.0500 L, so [Ag⁺] = 2.50 × 10⁻² M.
Thermodynamics, kinetics, equilibrium
ΔG° = ΔH° − TΔS° predicts spontaneity under standard conditions; ΔH alone does not. Rate depends on concentration, temperature, activation energy, and catalysts; equilibrium constant K depends on temperature. Compare Q with K to predict direction; Le Châtelier shifts are concentration, pressure/volume, and temperature effects. For acids, pH = −log[H₃O⁺], and buffers resist pH change when conjugate acid–base concentrations are comparable.
Traps that cost marks
- Using the smaller concentration as limiting without converting to moles.
- Forgetting that concentrations after mixing use total volume.
- Rounding molar masses or intermediate moles too early; carry extra digits, then apply significant figures.
- Treating ΔH < 0 as automatically spontaneous, or confusing rate with equilibrium position.
- Confusing molecular shape with electron-pair geometry when lone pairs are present.