Atomic Mass of Chlorine
| Value | 35.4499999627 Da (0.03545 kg/mol) |
| Status | Measured: ± 0.01 Da (2.8 × 10⁻⁴ relative), standard uncertainty |
| Source | IUPAC |
| Categories | Chemistry |
| Unit | Value |
|---|---|
| dalton (as molar mass) | 35.45 Da |
| gram per mole | 35.45 g/mol |
| kilogram per mole | 0.03545 kg/mol |
| kilogram per kilomole | 35.45 kg/kmol |
| milligram per millimole | 35.45 mg/mmol |
| pound per pound-mole | 35.45 lb/lb-mol |
| kilodalton (as molar mass) | 0.03545 kDa |
Learning zone
Chlorine is the element every teacher reaches for when explaining why atomic weights are not whole numbers: it is roughly 76 % ³⁵Cl and 24 % ³⁷Cl, and the weighted average lands at 35.45 g/mol. No individual chlorine atom weighs anything like that. Mass spectrometry makes the mixture visible in another way: any chlorine-containing fragment shows a companion peak two mass units higher at about a third the intensity, a fingerprint analysts use to spot chlorinated compounds at a glance.
IUPAC quotes chlorine only to four figures, with an interval of 35.446 to 35.457, because the isotope ratio varies measurably between seawater, rock salt and industrial sources. In water treatment the number converts free chlorine residual to moles of oxidant, and it carries into hypochlorite dosing: sodium hypochlorite is sold by "available chlorine", which is expressed in terms of Cl₂ at 70.90 g/mol rather than the sodium salt itself.
Moles from Mass (n = m/M)
Cite this page
formula.expert. (2026, October 16). Atomic Mass of Chlorine. https://formula.expert/constants/atomic-mass-chlorine