Composition and average molecular weight of benzene derivatives
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The concentration of benzene hydrocarbons in gas is usually expressed in g/m³. If the concentration of benzene hydrocarbons in gas is a (g/m³), the volume concentration can be calculated using the formula: y = 22.44a/(1000M), where M represents the average molecular weight of crude benzene (benzene hydrocarbons). Question: How is the average molecular weight of crude benzene determined? (The usual reasoning is: once the components of crude benzene and their molar ratios are known, the average molecular weight can be calculated.) But it’s difficult to determine the components of crude benzene and their molar ratios. ）
The average molecular weight of crude benzene is usually calculated by knowing its main components and their respective molar proportions. First, a chemical analysis must be conducted to determine the content or proportion of various aromatic hydrocarbons in crude benzene. Common aromatic hydrocarbons include various compounds such as benzene, toluene, xylene, and ethylbenzene; each of these compounds has its own molecular weight. The steps to calculate the average molecular weight of crude benzene are as follows: 1. Determine the mole fraction (proportion) of each aromatic hydrocarbon in the crude benzene sample. This data usually comes from chemical analysis techniques such as gas chromatography analysis. 2. Find the molecular weight of each aromatic hydrocarbon. For example, the molecular weight of benzene is 78 g/mol, that of toluene is 92 g/mol, and that of xylene is 106 g/mol, etc. 3. Use the formula: Average molecular weight M = Σ(molecular weight of each component × mole fraction of that component). That is, the sum of the molecular weights of all components multiplied by their mole fractions. Since the composition and ratios of crude benzene can vary in practice, it is difficult to accurately calculate the average molecular weight in the absence of specific composition data. If detailed component data is not available, typical values or industry standard values can be used as a reference. .