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Molar Mass Determination.docx

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Darren De Lorey

Molar Mass Determination PV = (mRT/M) Gas Densities d = m/V = (n x M)/ V = (n/V) x M Therefore: d = m / v = (MP/RT) The density of gases differs from that of solids and liquids in two important ways. 1. Gas densities depend strongly on pressure and temperature, increasing as the gas pressure increases and decreasing as the temperature increases. Densities of liquids and solids also depend somewhat on temperature, but they depend far less on pressure. 2. The density of a gas is directly proportional to its molar mass. No simple relationship exists between density and molar mass for liquids and solids. Mixture of Gases John Dalton proposed that in a mixture, each gas expands to fill the container and exerts the same pressure (partial pressure) that with if it were alone in a container. This was the basis of Dalton’s law of partial pressures. It states that the total pressure of a mixture of gases is the sum of the partial pressures of the components of the mixture. This rule also formed the basis of a shared principle. n An =tot/P A V tot= x A tot A The term nA/n totis given a special name, the mole fraction of Ax A. Collecting a gas over liquid (definition not important, but known the mathematics of it.) Water collected in a pneumatic trough is said to be collected over water and is “wet.” It is a mixture of two gases – The desired gas and water vapour, both filling a container with partial pressure. KINETIC-MOLECULAR THEORY  Gas is composed of a very large number of extremely small particles (molecules or, in some cases, atoms) in constant, random, straight-line motion) - 1 -  Molecules of a gas are separated by great distances. The gas is mostly empty space (the molecules are treated as so-called point masses, as though they have mass but no volume).  Molecules collide only fleetingly with one another and with the walls of their container, and most of the time, molecules are not engaged in collisions.  There are assumed to be no forces between molecules except very briefly during collisions. That is, each molecule acts independently of all others and is unaffected by their presence, except during collisions.  Individual molecules may gain or lose energy as a result of collisions. In a collection of molecules at constant temperature, however, the total energy remains constant. Deriving the
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