Dr. Zellmer
Chemistry 125
Tuesday
Time: 30 mins
Winter Quarter 2012
January 3, 2012
Prequiz
Name
KEY
Rec. TA/time.
1.
(7 pts)
The amount of lead, Pb, in the air on a particular day is 1.60 x 10
!
10
lb/ft
3
.
What is the
mass (in
kg
) of lead in 2.00 m
3
?
(1 in = 2.54 cm, 1.000 lb = 453.6 g)
(You
MUST
use
dimensional
analysis
to receive
full
credit
!)
2.
(8 pts)
A quantity of heat equal to 600.0 cal is
REMOVED
from 40.0 g of water at an
initial
temperature of 45.0
o
C.
Calculate the
FINAL
temperature
(in
o
C).
(The specific heat of water
is 1.00 cal/g
C
°C)
Show your work
.
q
=
m
C
c
C
)
T
heat
(mass)
C
(sp.
heat)
C
(temp.
change)
q
=
 600.0 cal
(heat is removed or released so q is negative; exothermic)
Want initial temp. so must find
)
T first
q
&
600.0 cal
)
T
=

=

=
&
15.0
°C
m
C
c
(40.0 g)(1.00 cal/g
C
°C)
(3 s.f.)
)
T
=
T
f
&
T
i
T
f
=
T
i
+
)
T
45.0
(only known to tenths)
=
45.0
°C + (
!
15.0
°C)
 15.0

=
30.0
°C
(3 s.f.)
30.0 (to tenths place)
Copyright R. J. Zellmer, January 3, 2012
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3.
(3 pts) Correctly
name
or write the
formulas
for the following compounds.
Also
, are they ionic
or molecular?
Chromium (VI) sulfide
The roman numeral gives the charge on the chromium ion (+6).
Cr
6+
S
2
&
==>
CrS
3
IONIC
For future reference, you should know how many particles (ions) you get when you put an ionic
substance in water.
First of all it dissociates (comes apart).
That’s the easy part.
You also need
to remember that these polyatomic ions stay together in solutions (i.e. act as a single particle).
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 Winter '08
 Zellmer
 Chemistry, Thermodynamics, Energy, Heat, Molecule, Ion, R. J. Zellmer

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