If all lab groups have exactly the same size of flask (255 mL), and all groups took their unknown vapor to the same temperature (100.0 oC) and pressure (760.0 mmHg), how would the number of molecules within the different flasks compare? Would it vary with molar mass? How? Explain.ģ. While performing this experiment, ten lab groups have ten different unknown volatile liquids with a range of molar masses. McWilliams (McWil-liams, 1973) tted these charts to the following polynomial equation lnK a T1 T2 a T2 a T3. pressure and temperature that are valid up to around 6000 psi pressures or more. DePriester (DePriester, 1953) presented K-value charts for light hydrocarbons vs.
#DEPRIESTER CHART LOW PRESSURE FULL#
If a lab group did not keep the flask submerged in boiling water for a full ten minutes, and some unknown never vaporized, how would that affect the calculated molar mass? In other words, would it make the calculated value too high or too low? Explain why.Ģ. the correlation for pressures above the convergence pressure. Post Lab Questions: Answer the following questions using complete sentences. Convert the temperature to Kelvin and record in your lab notebook. This will be the temperature of the vapor. The temperature of the boiling water is 100.0 oC. Continue heating for 8 to 10 minutes after the water comes to a rolling boil. You will need two 600 or 800 mL beakers, and 3 or 4 boiling chips.Īdd 3 or 4 boiling chips to the water in an 800 mL beaker and heat the water to the boiling point. Obtain an unknown liquid and a 3 inch aluminum foil square. You will record your data and calculations in your lab notebook. The mass of the condensed liquid is determined and the molar mass is calculated as described above.īefore weighing your condensed vapor, thoroughly dry the outside of the flask and make sure that no water is trapped under the foil coverĭo not rinse your flask with water between trialsĭispose of waste in appropriate container The temperature of the vapor equals the temperature of the boiling water bath. As with all gases, the vapor occupies the entire volume of its container. The vapor forces air from the flask until the pressure within the flask equals the barometric pressure of the lab. In this experiment, an unknown volatile liquid is heated in a boiling water bath and is vaporized. MM= mass of vapor in grams/moles of vapor The number of moles of gas is found byīecause the molar mass (MM) is defined as the mass of one mole of substance in units of g/mol, the molar mass of the vapor can be determined by Using the expression PV=nRT where R equals the Ideal Gas Constant 0.0821 L*atm/K*mol, one can determine the quantity of gas under given conditions of pressure, volume and temperature. The Ideal Gas Law mathematically relates the quantities of pressure (P in atm), volume (V in liters), and temperature (T in Kelvin) and the quantity of gas (n in moles). Given the mass of vapor at conditions of known pressure, volume, and temperature, one can determine the molar mass of the vapor. Please give me Post lab questions 2 and 3 at the bottom.Įxperiment 7 - Molar Mass of a Volatile Liquid
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