valence

Part II

The free-response half of the national exam: 96 real problems, 489 sub-parts. Type an answer or photograph your written work, and every part comes back scored against the official key with what was missing.

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8 minutes
2026 · Problem 5 · 12 pointsNet Ionic and Organic Reaction EquationsSix short answers, one line each, and no figures to read. The fastest way to see what the grader gives you back.

Stoichiometry and solutions

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Copper hydrates: dehydration, spectroscopy, iodometric titration2025 · Problem 1 · Stoichiometry and lab · 6 parts13 ptUnknown Group 2 Metal Halide Identification2024 · Problem 1 · Stoichiometry and lab · 5 parts11 ptIdentifying an Ionic H-N-O Compound2023 · Problem 1 · Stoichiometry and lab · 5 parts22 ptChlorofluorocarbon molar mass, Cl titration, isomers2022 · Problem 1 · Stoichiometry and lab · 4 parts11 ptIdentifying a Volatile Binary Oxide2021 · Problem 1 · Stoichiometry and lab · 5 parts13 ptIdentifying a Halogenated Carbon Oxide Gas2020 · Problem 1 · Stoichiometry and lab · 5 parts14 ptStudtite decomposition and uranium oxidation state2019 · Problem 1 · Stoichiometry and lab · 5 parts12 ptUnknown Monoprotic Acid: Analysis and Titration2018 · Problem 1 · Stoichiometry and lab · 5 parts13 ptFertilizer combustion analysis and freezing point2017 · Problem 1 · Stoichiometry and lab · 4 parts12 ptUnknown Carbon–Oxygen–Chlorine Compound Identification2016 · Problem 1 · Stoichiometry and lab · 4 parts12 ptMetal Carbonate/Oxide Mixture and CO2 Vibrations2014 · Problem 1 · Stoichiometry and lab · 6 parts13 pt

Descriptive and laboratory

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Net Ionic and Organic Reaction Equations2026 · Problem 5 · Net equations · 6 parts12 ptNet Equations for Six Reactions2025 · Problem 5 · Net equations · 6 parts12 ptWriting Net Ionic and Organic Equations2024 · Problem 5 · Net equations · 6 parts12 ptNet ionic equations for six reactions2023 · Problem 5 · Net equations · 6 parts12 ptNet ionic equations for six reactions2022 · Problem 5 · Net equations · 6 parts12 ptNet Equations for Six Reactions2021 · Problem 5 · Net equations · 6 parts12 ptNet equations for six reactions2020 · Problem 5 · Net equations · 6 parts12 ptNet ionic equations for six reactions2019 · Problem 5 · Net equations · 6 parts12 ptNet ionic equations for six reactions2018 · Problem 5 · Net equations · 6 parts12 ptNet ionic equations for six reactions2017 · Problem 5 · Net equations · 6 parts12 ptNet Ionic Equations for Six Reactions2016 · Problem 5 · Net equations · 6 parts12 ptNet ionic, organic and nuclear equations2014 · Problem 6 · Structure and redox · 5 parts10 pt

States of matter

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Unknown C,H,O Compound: Formula and Phase Properties2026 · Problem 1 · Stoichiometry and lab · 6 parts12 ptPerovskite CsPbI3 and YBa2Cu3O7 Structures2025 · Problem 7 · Bonding and solids · 6 parts19 ptVapor Pressure and Freezing Point of MgCl2 Solution2023 · Problem 4 · Kinetics · 5 parts13 ptBoiling points and intermolecular forces2021 · Problem 7 · Bonding and solids · 5 parts12 ptLithium halide rock salt lattices2018 · Problem 6 · Structure and redox · 5 parts24 ptSilicon unit cell and semiconductor bands2017 · Problem 6 · Structure and redox · 4 parts12 pt

Thermodynamics

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Hydrogen Storage in Lanthanum Pentanickel2026 · Problem 3 · Thermodynamics · 4 parts17 ptThermochemistry of DMEA–acetic acid neutralization2025 · Problem 3 · Thermodynamics · 4 parts12 ptHydrogen Combustion Thermodynamics and Flammability2023 · Problem 3 · Thermodynamics · 5 parts12 ptBromine thermodynamics, bond dissociation and entropy2022 · Problem 3 · Thermodynamics · 6 parts14 ptNitryl chloride/nitrosyl chloride gas equilibrium thermodynamics2021 · Problem 4 · Kinetics · 5 parts13 ptMond process thermodynamics of nickel carbonyl2020 · Problem 3 · Thermodynamics · 5 parts13 ptThermodynamics of Potassium Iodate Dissolution2018 · Problem 2 · Equilibrium · 4 parts12 ptThermodynamics of NO2 dimerization2017 · Problem 4 · Kinetics · 5 parts13 ptNitrogen Oxides: Thermodynamics and Equilibrium2014 · Problem 2 · Equilibrium · 6 parts14 pt

Kinetics

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Iodomethane hydrolysis kinetics and pH dependence2026 · Problem 4 · Kinetics · 5 parts19 ptEthene polymerization kinetics and thermodynamics2024 · Problem 3 · Thermodynamics · 6 parts13 ptIodine clock kinetics of peroxide-iodide reaction2022 · Problem 4 · Kinetics · 6 parts15 ptBrO Decomposition Kinetics with Ozone2020 · Problem 4 · Kinetics · 5 parts12 ptAscorbic acid oxidation by ferricyanide kinetics2019 · Problem 4 · Kinetics · 4 parts13 ptOrganoiridium Air Oxidation Kinetics2018 · Problem 4 · Kinetics · 4 parts15 ptOzone decomposition kinetics and mechanism2017 · Problem 3 · Thermodynamics · 5 parts13 ptHydrolysis kinetics of acetylsalicylate ion2016 · Problem 4 · Kinetics · 4 parts15 ptRate law for NO oxidation2014 · Problem 5 · Net equations · 6 parts13 pt

Equilibrium

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Nickel(II) complex ions and solubility equilibria2026 · Problem 2 · Equilibrium · 6 parts14 ptCalcium oxalate solubility and oxalic acid equilibria2025 · Problem 2 · Equilibrium · 6 parts13 ptpH-dependent solubility of calcium fluoride2024 · Problem 2 · Equilibrium · 5 parts14 ptAcidity and Solubility of Zinc Species2023 · Problem 2 · Equilibrium · 5 parts14 ptAmmonia/ammonium chloride buffer with silver2022 · Problem 2 · Equilibrium · 6 parts16 ptCalcium Hydroxide Solubility and Sulfuric Acid Titration2021 · Problem 2 · Equilibrium · 4 parts12 ptFluorescent indicator HPTS and phosphate buffers2020 · Problem 2 · Equilibrium · 5 parts13 ptIodate solubility products and van't Hoff analysis2019 · Problem 2 · Equilibrium · 5 parts14 ptCopper–Iodide Solubility, Complexation, Disproportionation2017 · Problem 2 · Equilibrium · 4 parts12 ptAcetic acid/acetate buffer pH calculations2016 · Problem 2 · Equilibrium · 4 parts12 ptSolubility Equilibria of Barium and Lead Fluorides2014 · Problem 3 · Thermodynamics · 6 parts14 ptAcid Strength and Leveling Effects2014 · Problem 8 · Organic · 3 parts12 pt

Oxidation and reduction

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Group 11 Alloy: Dissolution and Electrolysis2026 · Problem 6 · Structure and redox · 5 parts21 ptZn–Pb galvanic cell thermodynamics from E(T)2025 · Problem 4 · Kinetics · 5 parts12 ptConcentration Cell with Copper–Ammonia Complex2024 · Problem 4 · Kinetics · 5 parts13 ptPlatinum chloro complexes and electrolysis potentials2023 · Problem 6 · Structure and redox · 4 parts12 ptAg/Cu galvanic cell with oxalate2022 · Problem 6 · Structure and redox · 4 parts12 ptVanadium Redox Battery Potentials and Thermodynamics2021 · Problem 3 · Thermodynamics · 5 parts13 ptElectrolysis of acidified copper sulfate solution2020 · Problem 6 · Structure and redox · 6 parts13 ptElectrochemical Ammonia Synthesis from Nitrogen2019 · Problem 3 · Thermodynamics · 6 parts13 ptPotentiometric titration of chloride with silver2018 · Problem 3 · Thermodynamics · 4 parts13 ptLead acid battery thermodynamics and Nernst equation2016 · Problem 3 · Thermodynamics · 5 parts14 pt

Atomic structure and periodicity

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Group 1 elements: ionization, excited states, densities, decay2024 · Problem 6 · Structure and redox · 7 parts16 ptGroup 13 ionization energies, oxidation states, Lewis acidity2014 · Problem 7 · Bonding and solids · 6 parts12 pt

Bonding and molecular structure

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Boron hydrides: structure and bonding2026 · Problem 7 · Bonding and solids · 6 parts14 ptOxygen Allotropes: Bonding and Spectroscopy2025 · Problem 6 · Structure and redox · 5 parts13 ptDiazirinone: Lewis structures and bond enthalpies2024 · Problem 7 · Bonding and solids · 6 parts13 ptFluoride vs methyl compounds: boiling points and bond lengths2023 · Problem 7 · Bonding and solids · 6 parts13 ptFormamide vs. glyoxal bonding and properties2022 · Problem 7 · Bonding and solids · 4 parts12 ptMagnetism and Color of Transition Metal Complexes2021 · Problem 6 · Structure and redox · 5 parts13 ptSilicon Structure, Bonding, and Periodic Trends2020 · Problem 7 · Bonding and solids · 5 parts12 ptBeryllium versus barium: periodic trends and dimerization2019 · Problem 6 · Structure and redox · 6 parts13 ptBorazine Lewis structures, B–N bonding, boiling points2019 · Problem 7 · Bonding and solids · 5 parts13 ptNitric oxide bonding and N2O3 isomers2018 · Problem 7 · Bonding and solids · 4 parts13 ptOxygen and Sulfur Binary Fluorides2017 · Problem 7 · Bonding and solids · 5 parts14 ptH–H Potential Energy Curve and Vibration2016 · Problem 6 · Structure and redox · 5 parts12 ptBonding and Properties of Group 15 Halides2016 · Problem 7 · Bonding and solids · 5 parts12 pt

Organic and biochemistry

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HBr addition to (E)-2-pentene and isomers2026 · Problem 8 · Organic · 5 parts12 ptHalogenation reactions of organic compounds2025 · Problem 8 · Organic · 5 parts12 ptBasicity and reactivity of C4H9NO2 isomers and azoles2024 · Problem 8 · Organic · 5 parts12 ptCyclopentanone vs 1-methylcyclopentene reactivity2023 · Problem 8 · Organic · 5 parts12 ptC3H6O2 isomers: boiling points, chirality, hydration2022 · Problem 8 · Organic · 5 parts12 ptBromination of hydrocarbons and arenes2021 · Problem 8 · Organic · 5 parts13 ptC5H10 Isomers, Hydration, Stability, Chirality2020 · Problem 8 · Organic · 5 parts14 ptGrignard Synthesis and Alkene Dehydration2019 · Problem 8 · Organic · 4 parts12 ptAmide formation, basicity and resonance2018 · Problem 8 · Organic · 5 parts13 ptNitration of tert-Butylbenzene and Aniline Synthesis2017 · Problem 8 · Organic · 4 parts12 ptHBr addition to a branched alkene2016 · Problem 8 · Organic · 4 parts12 ptAmine structure, hybridization and basicity2014 · Problem 4 · Kinetics · 4 parts12 pt

Answers are graded by a model against the official rubric, so treat the score as a guide rather than an official mark. Five graded submissions a day.