Unit 03 · Stoichiometry & the Mole
Stoichiometry is the accounting of chemistry: the mole as the bridge between the atomic scale and the gram, balanced equations as conservation of mass made explicit, and the mole-ratio as the conversion that lets you predict exactly how much product a reaction can make. Mastery means you can carry a quantity from mass to moles to particles and back, find the limiting reagent, and reconcile theoretical with actual yield.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| The mole & molar mass | Treats the mole as just a big number with no use. | Converts grams to moles but slips on Avogadro's number or molar mass. | Moves fluently among mass, moles, and particles using molar mass and Avogadro's number. |
| Balancing equations | Changes subscripts to balance or leaves equations unbalanced. | Balances simple equations by trial but struggles with polyatomics. | Balances complex equations by adjusting coefficients only, conserving every atom. |
| Mole-ratio calculations | Ignores coefficients when relating reactants to products. | Uses the ratio but sets it up upside down at times. | Uses balanced coefficients to convert reliably between any two species in a reaction. |
| Limiting reagent & excess | Assumes reactants always run out together. | Identifies the limiter but cannot find leftover excess. | Determines the limiting reagent, the product amount, and the mass of excess remaining. |
| Percent yield (lab) | Reports product mass with no comparison to theory. | Computes theoretical yield but mishandles the actual measurement. | Measures actual yield, calculates percent yield, and explains sources of loss. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“I balanced the equation first, converted grams of magnesium to moles, used the mole ratio to get moles of product, then converted back to grams. Oxygen ran out first, so it’s the limiting reagent — that’s what caps the yield.”
“I multiplied the grams by the other number. A mole is a really big amount, right? I’m not sure which reactant runs out.”
You demonstrate this unit through a synthesis or precipitation lab where you predict the yield, run the reaction, and reconcile your measured product against theory aloud — not a multiple-choice test. A criterion counts as mastered only when you can both do the calculation and produce the matching result at the bench. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.