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How Molecular Weight Is Calculated From a Chemical Formula
Molecular weight is the sum of every atom's atomic weight in a molecule, counted according to the formula's subscripts — including atoms inside parentheses, which apply their multiplier to every element the parentheses group together, not just the last one.
Read guideMolarity vs Mass Concentration: Why You Need Molecular Weight to Convert
Molarity (mol/L) counts molecules, while mass concentration (mg/L or ppm) counts mass — the two can't be converted into each other directly, since the same molarity represents very different masses depending on how heavy the specific substance's molecules are; the missing link is always the substance's molecular weight.
Read guideWhat Does PPM Mean? Parts Per Million, Billion, and Trillion Explained
PPM (parts per million), ppb (parts per billion), and ppt (parts per trillion) are just very small percentages expressed with a different, more readable denominator — 1% equals exactly 10,000 ppm, so these units aren't a fundamentally different kind of measurement, just a rescaled way of writing the same dimensionless ratio.
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