Chemical Industry Tips – Molecular Weight

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The relative mass of molecules of elements and compounds, determined by comparing them to 1/12 of the mass of 12C. The molecular weight is equal to the sum of the atomic weights of all the atoms in a molecule. For example: the atomic weights of hydrogen and oxygen are 1.008 and 15.999 respectively, so the molecular weight of water = 1.008×2 + 15.999 = 18.015. Substances composed of molecules have a molar mass expressed in units of “g,” which numerically equals their molecular weight. For example, the molar mass of carbon dioxide is 44 g/mol, while the molar mass of water is 18 g/mol. Similarly, the molar mass of ionic compounds can be calculated. For example, the molar mass of sodium chloride is 58.5 g/mol. Because 1 mole of any substance composed of molecules contains 6.02×1023 molecules, and the mass of a single molecule can be calculated based on its molecular weight. For example, the molecular mass of carbon dioxide. The molecular weight of gas substances can be determined using the relative density method; the molecular weight of solute molecules in a solution can be determined using the boiling point elevation method or the freezing point depression method. Now, the molecular weight of substances can be determined quickly and accurately using mass spectrometry.