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

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
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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