Chem 171 Quiz 6 Version A (5 pts each) (Show work, unit, sig fig for full credit) Name Sec R = 0.08206 L atm mol-1 K-1 1. A glass vessel weighs 40.1305 g when clean, dry and evacuated; it weighs 138.2410 g when filled with water at 24.0 o C (density of water = 0.9970 g /mL) and 40.2959 g when filled with an unknown gas at 740.3 mmHg and 24.0 o C . What is the molar mass of the unknown gas? PV = nRT and R = 0.08206 L atm mol-1 K-1 Mass of water = 138.2410 g – 40.2305 g = 98.2205 g Vol of water (vessel) = 98.1105 g x 1 mL/0.9970 g = 98.41 mL Mass of gas = 40.2959 g – 40.1305 g = 0.1654 g T = 24.0 o C +273.15 = 297.2 K P = 740.3 mmHg x 1 atm /760 mmHg = 0.9741 atm M = mRT/PV = 0.1654 g x 0.08206 L atm mol-1 K-1 x 297.2 K / 0.9741 atm x 0.09841 L = 42.08 g/mol 2. The following “fill-in the blanks” questions refer to the experiment entitled “Physical Separation of a Ternary Mixture” a. The process of separating a solid or a precipitate from a liquid by whirling the mixture at a very high speed is known as centrifugation. b. If there is a yellow color in the flame of the Bunsen Burner, the air supply should be opened. Chem 171 Quiz 6 Version B (5 pts each) (Show work, unit, sig fig for full credit)
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