The mole is a counting unit sized so that grams and atomic masses line up.
A mole is 6.022 × 10²³ of anything. The odd number was chosen so that one carbon-12 atom weighs 12 amu and one mole of them weighs 12 grams. So the number on the periodic table means amu per atom and grams per mole at the same time. That's the bridge between the scale you can read and particles you can't count.
Pick a reaction, then tap a start and an end
Molar mass calculator
Type any formula. Parentheses work: Ca3(PO4)2, Al(OH)3, C12H22O11.
Mole map problems
How much lactic acid can a batch make?
Fermentation turns lactose into lactic acid: C₁₂H₂₂O₁₁ + H₂O → 4 C₃H₆O₃. Milk is about 4.8% lactose. In a 1,000 kg batch, that's 48 kg of lactose, or 48,000 g ÷ 342.30 g/mol = 140 mol. At 4 mol of lactic acid per mol of lactose, it could make up to 561 mol × 90.08 g/mol ≈ 50.5 kg of lactic acid.
A finished yogurt at ~1% TA has only fermented about a fifth of that. The rest of the lactose is still there, which is why yogurt keeps acidifying in the cooler and why "post-acidification" is a shelf-life spec. Notice the mass went up from 48 kg to 50.5 kg. That isn't an error. The water in the equation adds mass.
Common mistakes
- Going grams A → grams B directly. There is no such arrow. Mole ratios only work in moles.
- Multiplying by molar mass when you meant to divide. If grams don't cancel, flip it.
- Using the mole ratio from an unbalanced equation. Balance first.
- Using mL in molarity. M is mol per liter.
- Counting atoms in a formula wrong. Ca₃(PO₄)₂ has 8 oxygens, not 4.