Answer: C
Begin this problem by listing the known facts.
m = 2.00 g V = 0.821 liter T = 400. K P = 1.00 atm MW =?
You will need to use the ideal gas law to solve the problem: PV = nRT. Because moles can be
calculated by dividing the mass of the sample by its molecular weight, the ideal gas law be-
comes
PV m
=MWRT:
Solving for MW yields
..
...
mRTPV ./
1 00 0 821
2 00 0 0821 400
MW 80 0
atm liter mole K
g liter atm K
g mole
::
:
:
==:: =
__
_ __
ii
i ii
- A sample of zinc metal reacts completely with excess hydrochloric acid according to the
following equation:
Zn]s22g++ 2 HCl]]]aqggg"ZnCl aq H g
8.00 liters of hydrogen gas at 720. mm Hg is collected over water at 40.°C (vapor
pressure of water at 40.°C = 55 mm Hg). How much zinc was consumed by the reaction?
A.
.
/.
0 0821 313
720 760 8 00
:
:
^
^
h
h
B.
.
/
0 0821 2
760 720 313
:
:
^
^
h
h
C..
/..
0 0821 313
665 760 8 00 65 39
:
^^hh::
D.
..
/.
65 39 0 0821 313
665 760 8 00
::
:
^^
^
hh
h
E.
/.
..
665 760 0 0821
8 00 313 65 39
:
::
^^hh
Answer: C
Begin by listing the information that is known.
V = 8.00 liters H 2
P = 720. mm Hg −55 mm Hg = 665 mm Hg (corrected for vapor pressure)
T = 40.°C + 273 = 313K
Using the ideal gas law, PV = nRT, and realizing that one can determine grams from moles, the
equation becomes
./
/.
nH RTPV
0 0821 mole K 313 K
665 760 8 00
L atm
atm L H 2
2
::
:
==
`
_
j
i
Part II: Specific Topics