The classic mole road map: convert grams or particles of reactant A to grams or particles of product B, with every conversion factor (molar mass, Avogadro's number, mole ratio) shown live.
Stoichiometry is the calculation backbone of AP Chemistry Unit 4, and nearly every quantitative reaction problem — regardless of what's actually being asked — reduces to the same core sequence of conversions, commonly called the mole road map.
Starting from grams of a given substance, dividing by molar mass converts to moles — the universal "chemical currency" that lets different substances be compared on equal footing regardless of how much any one of them weighs. From moles of the given substance, multiplying by the mole ratio taken directly from the balanced equation's coefficients converts to moles of any other substance in the reaction — this single step is where the actual chemistry (which reaction, which coefficients) enters the calculation; every other step is pure unit conversion.
From moles of the target substance, multiplying by its molar mass converts back to grams, giving a mass-to-mass calculation overall. Alternatively, multiplying moles by Avogadro's number (6.022 × 10²³) converts to a count of individual particles — atoms, molecules, or formula units — useful when a problem asks "how many molecules" rather than "how many grams."
The power of the mole road map is that it handles any starting and ending unit combination using the exact same logical structure: grams-to-grams, grams-to-particles, particles-to-moles, or any other combination is just a different entry and exit point on the same map, never a fundamentally different calculation. Most stoichiometry errors come not from any individual conversion step being wrong, but from skipping the mole ratio step entirely and trying to convert directly between grams of two different substances — which is dimensionally meaningless without first passing through moles and the balanced equation's ratio.
This mapper displays every conversion factor explicitly and live as you work through a problem — molar mass, Avogadro's number, and the mole ratio from the balanced equation — turning the often-memorized "mole map" diagram into a tool that shows its work at every single step.