Cliffs AP Chemistry, 3rd Edition

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

5. 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