While performing the Dumas experiment, if the outside of the flask were not completely dry (Part I), how would this affect the calculated molar mass of the unknown volatile liquid? Would it be higher or lower? Explain.
1.) While performing the Dumas experiment, if the outside of the flask were not completely dry (Part I), how would this affect the calculated molar mass of the unknown volatile liquid? Would it be higher or lower? Explain.
2.) While determining the pressure during the Dumas experiment, if the barometric pressure reported were lower than the actual vapor pressure (Part I), how would this error affect the calculated molar mass of the unknown volatile liquid? Explain.
3.) While determining the volume during this experiment (Part II), if the total volume of the flask were incorrectly reported as 125 mL, how would this error affect the calculated molar mass of the unknown volatile liquid? Explain.
4.) Calculate the number of moles of Argon gas contained in a 4.00 dm3 container at 620. kPa and 25.0 oC. If the gas is Helium instead of Argon, will the answer change? Explain.
5.) In the Dumas method for determining the molar mass of an unknown volatile liquid, a sample of a volatile liquid that boils below 100 oC is vaporized in a boiling water bath and the mass of the vapor required to fill the flask is determined. The following data was collected:
|
Flask Volume |
100.0 +100.0 + 79.6 mL = 279.6 mL |
|
Mass of Flask + Cap |
143.85 g |
|
Mass of Flask + Condensed Liquid |
144.95 g |
|
Mass of Condensed Liquid |
1.10 g |
|
Temperature of Water Bath (oC) |
84.1 oC |
|
Barometric Pressure (atm) |
0.985 atm |
a.) What is the molar mass of the unknown?
b.) What will its temperature be when the pressure is 1.20 atm and the volume is 250.0 mL?
6.) Chemical analysis of an unknown compound shows that it contains 64.9%C, 13.5%H, and 21.6% O by mass. At 120 oC and 750 mmHg, 2.00 L of the gaseous compound weighs 4.60 g.
a.) What is the empirical formula of the compound?
b.) What is the molar mass of the compound?
c.) What is the molecular formula of the compound?
7.) Air is composed of approximately 78% N2, 21% O2 and 1% percent other gasses. Calculate the density of He at STP and explain why a closed balloon filled with He rises in air.
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