4-5:
Freezing
Point
Depression
If youdissolve a substancesuch as ordinarytable salt (NaCl) in wa
t
er, the freezi
n
g point of the water will decrease re
l
a
t
ive to the freezing point ofthe pure water. This property is used tomelt the snow or ice on roads during
t
he winter or to make homemade ice crea
m
. In this ass
i
gn
m
ent,
y
ouwill dissolve a sa
m
p
l
e
of NaCl in water, add s
o
me ice, andthen measure the freezing point depression.
1.
Start
VirtualChemLab,
select
Colligative Properties,
and select
Freezing Po
i
nt Depression
fr
o
mthe list of assign
m
ents. The lab will open in
t
he Calor
i
m
etry laborato
r
ywith a beaker containing45.00g of iceand a coffee cup calor
i
m
e
t
er on the lab ben
c
h. A sa
m
pleof sodiumchloride (NaCl) will also be on the balance.
2.
Click on the
Lab Book
toopen it. Record the
m
a
ss
o
f the sodiumchloride in the data table. If it is too s
m
all to read,click on the
Balance
areato zoomin, record the
m
a
ss, and then re
t
urn to
t
h
e laborato
r
y
.
3.
100
m
L of water is alrea
d
y in the calorimeter. Use t
h
e densityofwater at 25
o
C (0.998 g/
m
L) to deter
m
ine the mass fr
o
m the volu
m
e andrecord it in the data table. Make certainthe stirrer is
On
(you shouldbe able to see the shaft rotating). In thether
m
o
m
eter window, click
Save
to begin recording data in the lab book.Allow 20-30seconds to obtain a baseline te
m
perature of the water. Click the clock on the wall
l
abeled
Acce
l
erate
to acce
l
erate the laboratory t
i
m
e if necessar
y
.
4.
Drag the beaker of ice until it snaps into place above the calor
i
m
e
t
er and then pour the ice into the calori
m
eter.Click the ther
m
o
meter and graph windowsto bring
th
emto the front andobserve the change inte
m
peratu
r
e in the graph
w
indow u
n
til it reacheszero.Drag the we
i
gh paper fromthe balance to the calori
m
eter and thenpour
i
t intothe calori
m
eter. Observe the change in te
m
perature until it reaches a stable
m
i
n
i
m
u
mand cl
i
ck
Stop
in thete
m
peraturewindow. A data link
icon
will
appear in the lab book. Cl
i
ck the d
a
ta link icon and r
e
cord the
lowest
te
m
pe
r
ature after adding the salt
in the data table. (Re
m
ember that the watermayhave begun to w
a
rmback up.)
5.
If you want
t
orepeat the experiment, click on the r
e
ddisposal bucket to clear the lab, click onthe Stockroo
m
, click on the cl
i
pboard, and select P
r
eset
E
xperiment #1, Freezing Point Depression – NaCl.
Data
T
a
ble
mass NaCl
mass wa
t
er
mass ice
mass wa
t
er +ice
m
in
i
m
u
mt
e
m
p
e
r
a
tur
e
6.
The freezing pointdepression can be pr
e
dicted using the equation
∆
T=K
f
x
m
x
i
, where
∆
T
is
t
he
change in freezing point,
i
is the nu
m
ber of ions
i
nthesolutionper
m
ole of
dissolved NaCl
(
i
= 2),
m
is the
m
o
lality of the so
l
ut
i
on, and
K
f
isthe
m
olal freezing po
i
nt constant for water which is
1.86
o
C
/
m
.
107
Virtual ChemLab: General Che.
4-5FreezingPointDepressionIf youdissolve a substancesuch .docx
1. 4-5:
Freezing
Point
Depression
If youdissolve a substancesuch as ordinarytable salt (NaCl) in
wa
t
er, the freezi
n
g point of the water will decrease re
l
a
t
ive to the freezing point ofthe pure water. This property is used
tomelt the snow or ice on roads during
t
he winter or to make homemade ice crea
m
. In this ass
i
gn
m
ent,
y
ouwill dissolve a sa
m
p
l
e
of NaCl in water, add s
o
me ice, andthen measure the freezing point depression.
1.
2. Start
VirtualChemLab,
select
Colligative Properties,
and select
Freezing Po
i
nt Depression
fr
o
mthe list of assign
m
ents. The lab will open in
t
he Calor
i
m
etry laborato
r
ywith a beaker containing45.00g of iceand a coffee cup calor
i
m
e
t
er on the lab ben
c
h. A sa
m
pleof sodiumchloride (NaCl) will also be on the balance.
2.
Click on the
Lab Book
toopen it. Record the
3. m
a
ss
o
f the sodiumchloride in the data table. If it is too s
m
all to read,click on the
Balance
areato zoomin, record the
m
a
ss, and then re
t
urn to
t
h
e laborato
r
y
.
3.
100
m
L of water is alrea
d
y in the calorimeter. Use t
h
e densityofwater at 25
o
C (0.998 g/
m
L) to deter
m
ine the mass fr
4. o
m the volu
m
e andrecord it in the data table. Make certainthe stirrer is
On
(you shouldbe able to see the shaft rotating). In thether
m
o
m
eter window, click
Save
to begin recording data in the lab book.Allow 20-30seconds to
obtain a baseline te
m
perature of the water. Click the clock on the wall
l
abeled
Acce
l
erate
to acce
l
erate the laboratory t
i
m
e if necessar
y
.
4.
Drag the beaker of ice until it snaps into place above the calor
i
m
e
t
5. er and then pour the ice into the calori
m
eter.Click the ther
m
o
meter and graph windowsto bring
th
emto the front andobserve the change inte
m
peratu
r
e in the graph
w
indow u
n
til it reacheszero.Drag the we
i
gh paper fromthe balance to the calori
m
eter and thenpour
i
t intothe calori
m
eter. Observe the change in te
m
perature until it reaches a stable
m
i
n
i
m
u
mand cl
i
ck
Stop
6. in thete
m
peraturewindow. A data link
icon
will
appear in the lab book. Cl
i
ck the d
a
ta link icon and r
e
cord the
lowest
te
m
pe
r
ature after adding the salt
in the data table. (Re
m
ember that the watermayhave begun to w
a
rmback up.)
5.
If you want
t
orepeat the experiment, click on the r
e
ddisposal bucket to clear the lab, click onthe Stockroo
m
, click on the cl
i
pboard, and select P
r
7. eset
E
xperiment #1, Freezing Point Depression – NaCl.
Data
T
a
ble
mass NaCl
mass wa
t
er
mass ice
mass wa
t
er +ice
m
in
i
m
u
mt
e
m
p
e
r
a
tur
e
8. 6.
The freezing pointdepression can be pr
e
dicted using the equation
∆
T=K
f
x
m
x
i
, where
∆
T
is
t
he
change in freezing point,
i
is the nu
m
ber of ions
i
nthesolutionper
m
ole of
dissolved NaCl
(
i
= 2),
m
is the
m
10. Colligat
i
ve Properties
Calculate the predicted change in freezing point for
y
our solution.
7.
The change in freezing point
m
ust be s
u
btractedfr
o
m the freezing pointof purewater, whichis 0.0
o
C, in order to co
m
pa
r
e the predicted freezing pointwith the actual freezing point.
11. What is the calculated freezing po
i
nt of
t
h
e solution?Compare this to the actualfreezing poin
t
.
