Molecular Weight of Substances
The molecular weight of a substance, also called the molar mass , M, is the mass of 1 mole of that substance, given in M gram.
In the SI system the unit of M is (kg/kmol) and in the English system the unit is (lb/lbmol), while in the cgs system the unit of M is (g/mol). Molecular weight is represented by the same number in all unit systems regardless of the system used. For this reason, in many cases the unit for the molecular weight is not mentioned; however, one must realize that it is not a dimensionless parameter.
The molecular weight of a pure compound is determined from its chemical formula and the atomic weights of its elements. The atomic weights of the elements found in organic substances are C = 12.011, H = 1.008, S = 32.065, O = 15.999, and N = 14.007.
Example: The molecular weight of ethanol (C2H5 OH)
To calculate the molecular weight of ethanol, the molecular weight of each atom in the molecule is summed:
Methanol = 2*12.011(kg/kmol) + 6*1.008(kg/kmol) + 1*15.999 (kg/kmol) = 46.069 (kg/kmol)
See also Physical data for hydrocarbons, Physical data for alcohols and carboxylic acids, Physical data for organic nitrogen compounds and Physical data for organic sulfur compounds
| Substance |
Molecular Weight |
|---|---|
| Acetylene, C2H2 | 26.038 |
| Air | 28.966 |
| Ammonia (R-717) | 17.02 |
| Argon, Ar | 39.948 |
| Benzene | 78.114 |
| n - Butane, C4 H10 | 58.124 |
| 1,2 - Butadiene | 54.092 |
| 1-Butene | 56.108 |
| cis -2-Butene | 56.108 |
| trans-2-Butene | 56.108 |
| Butylene | 56.06 |
| Carbon Dioxide, CO2 | 44.01 |
| Carbon Disulphide | 76.13 |
| Carbon Monoxide, CO | 28.011 |
| Chlorine | 70.906 |
| Cyclohexane | 84.162 |
| Cyclopentane | 70.135 |
| n - Decane | 142.286 |
| Deuterium | 2.014 |
| 2,3 - Dimetylbutane | 86.178 |
| 2,2 - Dimethylpentane | 100.205 |
| Diisobutyl | 114.232 |
| Duoderane | 170.21 |
| Ethane, C2H6 | 30.070 |
| Ethene | 28.05 |
| Ethyl Alcohol | 46.07 |
| Ethylbenzene | 106.168 |
| Ethyl Chloride | 64.515 |
| 3 - Ethylpentane | 100.205 |
| Ethylene, C2H4 | 28.054 |
| Fluorine | 37.996 |
| Helium, He | 4.002602 |
| n - Heptane | 100.205 |
| n - Hexane | 86.178 |
| Hydrochloric Acid | 36.47 |
| Hydrogen, H2 | 2.016 |
| Hydrogen Chloride | 36.461 |
| Hydrogen Sulfide | 34.076 |
| Hydroxyl, OH | 17.01 |
| Isobutane (2-Metyl propane) | 58.124 |
| Isobutene | 56.108 |
| Isooctane | 210.63 |
| Isopentane | 72.151 |
| Isoprene | 68.119 |
| Isopropylbenzene | 120.195 |
| Krypton | 83.80 |
| Methane, CH4 | 16.043 |
| Methyl Alcohol | 32.04 |
| Methyl Butane | 72.15 |
| Methyl Chloride | 50.488 |
| Methylcyclohexane | 98.189 |
| Methylcyclopentane | 84.162 |
| 2 - Methylhexane | 100.205 |
| 2 - Methylpentane | 86.178 |
| Natural Gas | 19.00 |
| Neon, Ne | 20.179 |
| Neohexane | 86.178 |
| Neopentane | 72.151 |
| Nitric Oxide, NO | 30.006 |
| Nitrogen, N2 | 28.0134 |
| Nitrous Oxide, N2O | 44.013 |
| n - Nonane | 128.259 |
| n - Octane | 114.232 |
| Oxygen, O2 | 31.9988 |
| Ozone | 47.998 |
| n - Pentane | 72.151 |
| Pentylene | 70.08 |
| Propane, C3 H8 | 44.097 |
| Propene | 42.081 |
| Propylene | 42.08 |
| R-11 | 137.37 |
| R-12 | 120.92 |
| R-22 | 86.48 |
| R-114 | 170.93 |
| R-123 | 152.93 |
| R-134a | 102.03 |
| R-611 | 60.05 |
| Styrene | 104.152 |
| Sulfur | 32.02 |
| Sulfur Dioxide (Sulphur Dioxide) | 64.06 |
| Sulfuric Oxide | 48.1 |
| Toluene, toluol | 92.141 |
| Triptane | 100.205 |
| Xenon | 131.30 |
| o - Xylene, xylol | 106.168 |
| Water Vapor - Steam, H2O | 18.02 |
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