Canonical lesson CHEMISTRY20-U3-L28 · outcome 20-C2.8k · depth CURRICULUM_BASELINE

Unit C: Solutions, Acids, Bases and Equilibrium intro - outcome 20-C2.8k

• Course: CHEMISTRY20 (SCN2796)
• Lesson ID: CHEMISTRY20-U3-L28
• Official outcome: 20-C2.8k (KNOWLEDGE)
• Object type: canonical lesson (not a bootcamp session)
• Source: Alberta Chemistry 20 Program of Studies (2007, updated 2014)

Official outcome text

define Arrhenius (modified) bases as substances that produce OH-(aq) in aqueous solutions and recognize that the definition is limited

Learning intention

Meet 20-C2.8k 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

Modified Arrhenius base: produces OH−(aq) in water. NaOH(s) → Na+ + OH−. NH3(aq) + H2O ⇌ NH4+ + OH− also produces hydroxide, which is why the definition was modified. Limitation: bases in non-aqueous solvents, and species that accept H+ without producing OH− in water, strain the definition.

Worked example

Ca(OH)2 dissolves to give OH−. NH3 is a base by the modified definition because OH− appears. Metal oxides that give OH− with water (if discussed) sit at the edge.

Guided practice

1. Ca(OH)2 and NH3 (modified: OH− appears). Do not copy the teaching sentences unchanged.
2. Near-miss: calling NaCl a base because it has a metal. Mark the first wrong line.

Independent practice

1. NaOH as a clean fit.
2. Two sentences: why NH3 is included in the modified definition.
3. Limitation of the water-centred definition.

Diagram / whiteboard

Approved diagram id chem20-ph-scale - pH scale / solution concentration axes. 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

Defining bases only as “bitter and slippery” empirically and stopping, or tasting NaOH.

Safety and lab register

Setting: concentration and pH on paper or school-prepared dilute solutions. Red-cabbage indicator is classroom-supervised or photo/dataset. No concentrated acids or bases. No tasting. Dilution math is not a licence to mix cleaners. Forbidden: bleach+acid, drain opener, battery acid, undiluted pool chemicals. AI Tutor must not invent titrations or acid labs outside the register.

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

Formative evidence

Definition + Ca(OH)2 + NH3 notes.

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

AI Tutor / human tutor

Ground on 20-C2.8k. 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.