Guide
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If you were to calculate the molar mass any gas, would you take the value of the atomic weight of nitrogen, and multiply it by 2. As a result, the index would have received 28 grams / mole.But how to calculate the molar mass mixture gas ?This problem is solved elementary.We only need to know exactly which gases and in what proportion are part of the mix .
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Consider a specific example.Suppose you have gas th mixture that consists of 5% (by weight) of hydrogen, 15% nitrogen, 40% carbon dioxide, 35% oxygen and 5% chlorine.What is its molar mass?Use the formula for the mixture , consisting of components: mS = M1N1 + M2N2 + M3N3 + ... + MxNx, where M - the molar mass of the component, and N - its mass fraction
(percent concentration).
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molar mass gas you know, remembering the atomic weights of elements (here you need Periodic Table).Their mass fractions are known under the terms of the problem.Substituting the values ​​in the formula and performing calculations will receive: 2 * 0.05 + 28 * 0.15 + 44 * 0.40 + 32 * 0.35 + 71 * 0.05 = 36.56 g / mol.Here is the molar mass of said mixture .
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it possible to solve the problem in another way?Yes of course.Suppose you have the exact same mixture encased in a sealed container volume V at room temperature.How can you calculate the laboratory by its molar mass ?To do this, you need to first weigh the vessel on accurate scales.Mark it mass as M.
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Then, by connecting the manometer to measure the pressure P inside the vessel.Then, using a hose connected to a vacuum pump, pump the mixture little .It is easy to understand that the pressure inside the vessel is reduced.Close the valve, wait about half an hour to the mixture inside the vessel again took the ambient temperature.Check with a thermometer, measure the pressure of the mixture gauge.Indicate his P1.Weigh the vessel, a new label mass as the M1.
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Well, then remember the universal equation Mendeleev-Clapeyron.According to him, in both cases: - PV = MRT / m; - P1V = M1RT / m.Nemnogo modifying this equation, you will receive: - m = MRT / PV; - m = M1RT / P1V.
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It follows that m = (M - M1) RT / (P - P1) V.A m - that is the molar mass of the mixture gas , which you need to know.Substituting the known values ​​into the formula, you get a response.