Molar Mass Calculator

Calculates molar mass of a chemical compound by parsing its formula and summing atomic weights from the IUPAC standard atomic weights table. Supports element subscripts, parenthesized groups, and hydrate notation (e.g., CuSO4·5H2O).

Output is given in grams per mole (g/mol), the practical unit for laboratory stoichiometry. Standard atomic weights are abridged values from the latest IUPAC report; for high-precision work, consult the source for ranges.

The parser implements Hill notation conventions: capital letter starts an element symbol, optional lowercase letter completes a two-letter symbol, optional numeric subscript follows. Parentheses group subformulas, multiplied by their following subscript. The hydrate dot operator (·) introduces a separate water-of-hydration count. Unicode subscripts (H₂O) are normalized to ASCII (H2O) before parsing. Common shortcut notations like "d" for deuterium or "M" as a generic metal placeholder are not supported; explicit element symbols are required.

The summation is straightforward once parsed. For each element symbol multiplied by its count (recursing through parenthesized groups), look up the standard atomic weight and add to the running total. Standard atomic weights derive from the IUPAC Commission on Isotopic Abundances and Atomic Weights, which periodically revises values as measurement precision improves. Most elements have weights stable to four decimal places; sulfur, hydrogen, lithium, and a few others have wider natural variation and are reported as ranges.

A worked example for sucrose, C12H22O11. Atomic weights: C = 12.011, H = 1.008, O = 15.999. Calculation: 12 × 12.011 + 22 × 1.008 + 11 × 15.999 = 144.132 + 22.176 + 175.989 = 342.297 g/mol. Published values typically round to 342.30 g/mol. Per mole of sucrose contains 12 moles of carbon (144.13 g), 22 moles of hydrogen (22.18 g), and 11 moles of oxygen (175.99 g). Practical lab translation: weighing 342.30 g of sucrose dissolved in water yields one mole of solute.

Hydrate notation requires care. Copper sulfate pentahydrate, CuSO4·5H2O: 63.546 (Cu) + 32.06 (S) + 4 × 15.999 (O in sulfate) + 5 × 18.015 (5 H2O) = 249.685 g/mol. The anhydrous form (CuSO4) is 159.609 g/mol. Confusing the two introduces a 36% mass error in solution preparation. Reagent bottles label the form explicitly because the difference matters at this scale.

Limitations: the calculator uses standard terrestrial isotope abundances. Isotopically enriched samples (deuterated solvents, 13C-labeled compounds) require per-isotope calculation. Some elements with significant natural variation (sulfur sourced from different geological deposits varies by ±0.05 in atomic weight) make published molar masses approximate at the fifth decimal place. For analytical chemistry where precision matters, the IUPAC interval values rather than abridged single-point values should be used.