Safety and source boundary
Instruction uses fictional readings, numerical models, and paper-based SDS literacy. No mixing, heating, or handling chemicals is authorized. Use product-specific SDS information and approved supervision for any real laboratory activity.
Explicit instruction
A ratio model assumes that equal volumes of a homogeneous material have proportional masses under comparable conditions. For classroom analysis, use a fictional dataset rather than handling substances. A data table should include labels, units, repeated observations when available, and a note about how the measurements were obtained. Plotting mass against volume tests whether a constant slope is plausible. If measurements depart from the pattern, the first response is to inspect the method and uncertainty, not automatically delete the data.
Vocabulary: slope; ratio model; volume; prediction; residual.
Worked reasoning example
Simulated measurements: trial A mass=10.0 g, volume=4.0 mL; trial B mass=15.0 g, volume=6.0 mL; trial C mass=20.0 g, volume=8.0 mL. Each density is 2.5 g/mL. A mass-versus-volume plot has slope 2.5 g/mL and passes through the origin for this idealized model. These fictional numbers demonstrate proportionality, not a claim about a named real substance.
Guided practice
Identify the horizontal and vertical axes for a mass-versus-volume graph. Why does the slope have units g/mL?
Independent student task
- Make a three-row data table including ratio calculations with units.
- Predict model mass for 10.0 mL using the same modeled relationship and label it a prediction.
- Propose a realistic reason why real measurements might not lie exactly on the idealized line.
Misconception correction
A clean proportional line in invented data demonstrates the arithmetic model, not empirical verification.
Formative concept check
Does the simulated dataset prove every real chemical has constant density?
Reveal worked response
No. It models one assumed homogeneous material under selected conditions; real data and conditions must be investigated separately.
Self-check only; never an official exam or mastery attempt.
Teacher notes
Use only synthetic numbers or previously approved records. Do not invite mixing or physical measurements involving chemicals.
Learning record return
Record explanations, calculations, safety decisions, and corrections in the existing Week 01 classroom field. Existing local records and mastery authority remain unchanged.
Return to thursday Evidence Workspace