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q1w2.key - Dr Zellmer Time 23 mins Chemistry 122 Summer...

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Dr. Zellmer Chemistry 122 Wednesday 10:30 AM Time: 23 mins Summer Quarter 2008 June 25, 2008 Quiz I Name KEY Rec. Instr. 10:30 ---------------------------------------------------------------------------------------------------------------------------------------- 2 1. (5 pts) A sample of N gas occupies 10.00 L at 25°C and a pressure of 14.51 lb/in . At what 2 2 temperature (in °C ) will it occupy 20.00 L at a pressure of 0.9211 atm? (Mol. Wt.: N = 28.02) (1 atm = 101.325 kPa = 14.7 lb/in = 760 torr = 760 mm Hg) 2 Since P, V & T all change use the Combined Gas Law: 2 2 1 1 P V P V ------- = ------- T MUST be in kelvin 2 1 T T 1 1 1 P = 14.51 lb/in V = 10.00 L T = 25°C + 273.15 = 29 8 .15 K 2 14.7 lb/in 2 2 2 2 P = 0.9211 atm × ------------ = 13.5 4 0 lb/in V = 20.00 L T = ? 2 1atm 2 2 1 2 2 P V T P V 13.5 4 0 lb/in 20.00 L 2 2 1 T = ---------- = (-----)(-----)T = (----------------)(-----------) 29 8 .15 K = 55 6 .44 K = 28 3 .29°C 1 1 1 1 P V P V 14.51 lb/in 10.00 L 2 = 283°C (3 s.f.) 2. (7 pts) A gas with a molecular weight of 40.0 amu has a mass of 5.35 g at STP in a container of unknown volume. What is the volume (in L) of the container? STP => Standard Temp. & Pressure: T = 0°C (273.15K) & P = 1 atm To calculate the volume you need moles. You can get this from the molecular weight or molar mass, M , m mass m M = ---- = --------- or n = ----- (or use dimensional analysis) n moles M m 5.35 g 1 mol n = ---- = --------------- or ? mol = 5.35 g x --------- = 0.13 3 75 mol M 40.0 g/mol 40.0 g
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