Molecular Formula Calculator

Divide the molecular mass by the empirical formula mass and multiply every subscript by the whole-number result. CH₂O has a mass of 30.03; glucose measures 180.16, giving a multiplier of 6 and C₆H₁₂O₆.

Then one of the two masses is wrong. The ratio is a count of repeat units, so it must be a whole number within experimental error — a value like 5.4 signals a bad molar mass measurement or a miscalculated empirical formula, not a formula to round into.

Yes, when the multiplier is 1. Water, methane and carbon dioxide are all already at their simplest ratios, so no further reduction is possible.

Because the empirical formula only fixes the ratio, not the count. Formaldehyde, acetic acid and glucose are all CH₂O with multipliers of 1, 2 and 6 — which is exactly why the molar mass has to be measured separately.

Usually by mass spectrometry, which reads the molecular ion directly. Colligative methods such as freezing-point depression also work and are what a teaching lab is likely to use.

No. C₂H₆O is both ethanol and dimethyl ether, which behave nothing alike. Formula fixes composition; structure needs spectroscopy.

Mass spectrometry, which reads the molecular ion directly and gives the answer to a fraction of a mass unit. Colligative methods such as freezing-point depression or osmometry also work and are far less precise, which affects how clean a multiplier you should expect.

Distinguishing formulas of the same nominal mass. C₃H₈O and C₂H₄O₂ are both 60 to the nearest whole number, but their exact masses are 60.0575 and 60.0211 — a difference an instrument reading to four decimal places resolves outright.

(2C + 2 + N − H − X) ÷ 2, where X counts halogens. The result is rings plus π bonds. Benzene at C₆H₆ gives 4, which is one ring and three double bonds.

No. The molecular formula is the empirical formula repeated a whole number of times, so the multiplier is at least 1. A result below 1 means the molecular mass entered is smaller than the empirical formula mass, which cannot happen.

Then the multiplier is large and not fixed — a polymer sample contains chains of different lengths, so it has a distribution of molar masses rather than a single value. Number-average and weight-average molar masses are quoted instead, along with the dispersity between them.

It does in the formula mass. Copper sulfate pentahydrate is CuSO₄·5H₂O at 249.68 g/mol, not 159.61. Weighing out a hydrate as though it were anhydrous is one of the most common preparation errors in a teaching laboratory.