Teacher & parent educator · 5 daily lessons
Teaching notes, misconceptions, reference answers, differentiated learning and evidence criteria
For HS-PS1-2 and HS-PS1-7, build student models and reasoning about atom conservation. These lessons support—not alone complete—the performance expectations. Prerequisites: element symbols, chemical formulas and basic mass subtraction/addition.
Suggested daily pacing: 8 minutes phenomenon/prediction; 17 minutes reading/model; 15 minutes interactive or dataset inquiry; 10 minutes student notebook and rubric; 5 minutes retrieval and feedback.
Target: Define the measured system and distinguish disappearing mass from matter transferred elsewhere.
Teacher prompt: What observation would help distinguish gas escape from spilling or measurement error?
Class evidence: Record your prediction for an open versus closed boundary, define which matter is counted, and propose a different possible cause of apparent mass loss.
Target: Interpret coefficients, subscripts and physical state symbols without changing chemical identities.
Teacher prompt: Why must we never change a formula subscript to balance an equation?
Class evidence: Explain how the coefficient and subscript differ using 2H₂O and H₂O₂. Define all common state symbols and write a short explanation of why equation balancing alone is not proof of a reaction.
Target: Balance equations in simplest whole-number form and audit every element before accepting an answer.
Teacher prompt: Why does a chemical equation need equal atom totals but not equal numbers of molecules?
Class evidence: Solve at least seven unique equations in the interactive Balance Arena. Record atom ledgers for two and explain a corrected mistake.
Target: Model mass conservation in open and closed accounting systems while documenting uncertainty.
Teacher prompt: Which parts of the model are measured, computed or assumed?
Class evidence: Use the digital lab for at least three records including a matched open/closed pair. Describe two assumptions the simulation makes and a source of real-world measurement uncertainty.
Target: Use an atom ledger, mass balance, and evidence-based reasoning to defend a qualified chemical explanation.
Teacher prompt: What evidence would you need to identify an actual gas rather than assume its identity?
Class evidence: Write a complete CER with two numbers and units, one balanced atom ledger, a possible competing explanation and a proposed safe next investigation. Complete the ten-question check and export your notebook.
Fictional open mass example: 120.0 g initial, 3.6 g modeled gas escapes measured region, measured after = 116.4 g, complete accounted total 116.4 + 3.6 = 120.0 g. Closed accounting retains 120.0 g inside. This is an assumed model, NOT a real biological or chemical measurement.
Balanced equations for guided instruction: 2H₂ + O₂ → 2H₂O; N₂ + 3H₂ → 2NH₃; 4Fe + 3O₂ → 2Fe₂O₃; CH₄ + 2O₂ → CO₂ + 2H₂O; CaCO₃ → CaO + CO₂. Coefficients conserve every element; they are not gram quantities.
16/20 is 80%. Review constructed responses before recording educator marks.
Foundation: prefill an atom ledger; Core: solve seven puzzles and paired mass trials; Extension: compare ±0.2 g measurement uncertainty with a hypothetical 0.1 g difference.
Friday samples 10 of 20 items with feedback and 80% correction guidance. It is not a secure supervised midterm or final. Use teacher review and separately controlled examinations for authoritative assessment. The new daily journals use a separate browser-key namespace; the original weekly student records are preserved. JSON export is available; localStorage is not cross-device cloud sync.