Canonical lesson CHEMISTRY20-U4-L12 · outcome 20-D2.2k · depth CURRICULUM_BASELINE

Unit D: Quantitative Relationships in Chemical Changes - outcome 20-D2.2k

• Course: CHEMISTRY20 (SCN2796)
• Lesson ID: CHEMISTRY20-U4-L12
• Official outcome: 20-D2.2k (KNOWLEDGE)
• Object type: canonical lesson (not a bootcamp session)
• Source: Alberta Chemistry 20 Program of Studies (2007, updated 2014)

Official outcome text

identify limiting and excess reagents in chemical reactions

Learning intention

Meet 20-D2.2k with instruction, practice, and a check. The 10-session bootcamp does not replace this lesson.

Success criteria

1. Restate the outcome in classroom language without swapping in a different unit’s template.
2. Complete the worked-style task for this outcome.
3. Name the lab setting (classroom-supervised / teacher demo / dataset or simulation / forbidden).

Teaching

Limiting reagent is fully consumed; excess remains. Convert each reactant to moles of one product; the smaller product amount identifies the limiter. Do not compare grams of different formulas directly.

Worked example

2 H2 + O2 → 2 H2O. 4.0 mol H2 and 4.0 mol O2: H2 would make 4.0 mol H2O, O2 would make 8.0 mol H2O → H2 limiting, 2.0 mol O2 excess.

Guided practice

1. 2 H2 + O2 → 2 H2O. 3.0 mol H2 and 1.0 mol O2: limiting, excess, n(H2O). Do not copy 4.0/4.0 mol.
2. Near-miss: choosing the reactant with the smaller mass as limiting without moles. Mark it.

Independent practice

1. Mass version: 4.00 g H2 and 32.0 g O2 - limiting?
2. Two sentences: two theoretical yields, the smaller is real.
3. Leftover moles of excess.

Diagram / whiteboard

Approved diagram id chem20-stoich-mole-map - Mole map stoichiometry flow. Tutor may open the course whiteboard and display this id. Do not invent hazardous procedures on the board.

Checks for understanding

Use the formative evidence below as the exit check for this outcome. Correct the misconception named in this lesson before praising.

Misconception to repair

Picking the reactant with the smaller mass as limiting without moles.

Safety and lab register

Setting: stoichiometry on balanced equations and provided mass/volume data. Live combustion or precipitation is teacher demo or school lab SOP only - never a home task. Titration (if run) is school burette, dilute reagents, goggles; otherwise use the provided titration-curve dataset. Forbidden: student-run flames, concentrating acids, tutor-invented yields labs. AI Tutor must not invent procedures.

Alberta Poison Control if a real exposure is occurring: 1-844-764-7669. The AI Tutor is not a poison centre.

Formative evidence

One mole and one mass limiting-reagent problem.

This is not a diploma. Mastery needs instruction + activity + check.

AI Tutor / human tutor

Ground on 20-D2.2k. No false praise. No invented procedures. No silent skip to a different unit. Human tutor if the student describes mixing bleach, tasting, or flames.

Provenance

Official POS wording from ALBERTA_SENIOR_HIGH_OFFICIAL_OUTCOMES.csv. Pack lesson written to replace Wave-4 contaminated canonical markdown.