Question

Barometric pressure, in mmHg778. 3 in atm 02 Trial 1 Trial 2 Trial 3 Weight of empty Erlenmeyer flask and aluminum foil Weight of Erlenmeyer flask, foil and vapor after heating Weight of vapor 82. 1179 83-7079 b.5909 88 3549 103. 7%9 104.3199 0.549 88.8839 0.5399 Volume of flask in L Volume of the vapor o.1580L O.1530 L O.1540L Temperature in K 369-15K 367-(5K 3CE15K Calculate the molecu lar weight of the unknown. Be sure to convert units so that atmospheres, liters and Kelvin are used in the calculations. Show calculations for all the trials attempted below. Remember: Mw (Mass)RT: R=universal gas constant, 0.08206 L-atm/mol-K PV 1. This experiment gives fairly good results. However, it has a design flaw concerning the mass of the gas (liquid) inside the flask. On cooling the flask from its boiling point to room temperature, will all of the gas condense into a liquid? Explain why or why not. 2. If a sample of acetone vapor (CsHeO) occupies 250.0 mL at 100°C and 0.987 atm, what is its mass (in grams)? Show your calculations. 70

Answer 1

The molar mass of the gas is calculated:

MM = 0.59 g * 0.082 * 366.15 / 1.02 * 0.158 = 110 g / mol

Trial 2: 103 g / mol

Trial 3: 101 g / mol

Average = 105 g / mol

1) Yes, since the liquid must be boiled to measure its properties, if it is cooled to room temperature, it would be liquid again.

2) The mass of gas is calculated:

m = P * V * MM / R * T = 0.987 * 0.25 * 58.08 / 0.082 * 373 = 0.469 g

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