Experimenf
t17
Heqt of Fusion
of lce
Iaxt ref eref tc0:
Chapter 9,
pp
21
4-216
Introduction
Thc ;tntrlttn[ of cncrgy rc:cltrirccl [o convcrl it solrrl lo a Iiclurcl 1t constant
,
prcssul'c artd tctttpct'atul'c, is callcd thc lrt,ut ,l
.l'us'isrr gl' thc substance.
It is often convenient to speak of the moldr heat of fusion. The molar
heat of fusion is thc ilntortnI of cncrgy rcquirccl to cor]tplctcly .h1ngc
on(:
nrole of a solid, at its rnelting point, into rr liquicl
In this cxpcrirttcnl, thc rttolltt' hcrrr ol' lrrsion ol'ice: wif l lre
tle lcr.rrrirrcrl
'l'he equation
lor the change of'state involvecj is as f'ollows.
.
I
mol HzO(s)
+
I mol H:O( / )
The ice will be melted by placing it in a known volume
of hot water
contained in a plastic foam cup. The systenr will be
left undisturbed until
all the ice has melted. The amount of heat lost by the hot water
in this
process can be calculated according to the following
equation.
(
l)
molar hear of fusion
__+
heat lost
by water
water /\ capacity
temperature
of water
of water
The heat lost by the water will be absorbed by the meiting
ice, The
volume of ice that melts can be determined by measuring
the volume of
the water in the cup before the ice is added and after
the ice has melted.
(2) volLrme of melted ice
The mass of melted ice can
be
(3)
_
mass
water
volume of
initial volume of water
calculated from its volume and density.
x
cJensity
volume
If
the mass of the ice melted and the heat absorbed by the
ice are known,
the heat required to melt one mole of ice can be calculated.
(4) molar hear of fusion of ice
Objectives
l. To determine
heat absorbed by ice
rrass of ice melted
x
molar mass of ice
the molar heat of fusion of ice.
Equipment
2 safety goggles
1 plastic foam cup
1 100-mL graduated
1 250-mL beaker
1 400-mL beaker
1 gas burner
1
-t
I
cylinder
1
1
1
1
I
ring stand
ring support
wire gauze
thermometer
beaker tongs
spatu la
Heat of Fusion of lce
123
ry
Moteriqls
ice
E.
g
1',:
nlF'
Bgw
Sofety
l.
2.
Wear safety goggles.
Mercury is extremely toxic and a rnercury spill is very difficult to
If you break a mercury thermometer, report the incident to the
teacher immediately so that any spilled mercury can be cleaned up
thoroughly and disposed of properly.
clean up.
Procedure
As you perform the experiment, record your observations in Table I 7 .l
1.
.
Add approximately 100 mL of tap water to a 250-mL beaker, and
heat the water to 60"C, using a gas burner and standard ring stand assemice
bly. While the water is heating, fill a plastic foam cup halfway with
cubes. Place the cup in a 400-mL beaker for support.
2, When the temperature of the water has reached 60'C, use two 20-mL
portions of this hot water to preheat a 100-mL graduated cylinder. Rinse
the cylinder with each of the hot water portions and discard the rinses.
3.
Pour 30 mL of the hot water into the graduated cylinder. Record the
volume of this water to the nearest milliliter. Measure and record the temperature of the water to the nearest 0. I "C.
4.
C}
wr&J
Quickly drain any excess water from the ice cubes in the cup. Add
the measured hot water to the ice in the cup. Stir the ice water rapidly,
but with care, until its temperature falls to 2'C. At this point, some
unmelted ice should remain in the cup. If, in fact, all the ice has melted,
add a bit more so that some ice remains unmelted when the temperature
is 2'C or below. Record the lowest temperature of the mixture of ice and
water.
5.
Using a spatula, quickly remove any unmelted ice from the cup. As
you remove the ice, drain as much water as possible back into the cup.
()
O
6.
Carefully pour the cold water from the cup into the graduated cylinder
and record the final volume to the nearest milliliter.
a
AJ
(t)
.E
,:
Tqble
17'tl Doto
E
volume of hot water:
U
oo
;
initial temperature of hot water:
final temperature of water and melted ice:
.2
g(t))\
:lI
E
fr.t
final volume of water and melted ice:
;
\/,
124
Experiment 17
Name
Class
Date
Doto Anolysis
l ' calculate the change in the temperature
of the hot warer.
2'
calculate the heat lost by the hot water. (See
Equation I in the
) Express your answer in kilojoules. Remember that
the
specific heat capacity of water is 4. l g joules/(g
x "C) or I cal/(g x "C)
and that there are 1000 joules in I
kilojoule.
Introduction.
3.
Calculate the volume of ice melted.
4, Calculate the mass of ice melted.
is I glmL.
Rernember that the density of water
n
5.
calculate the molar heat of fusion of ice. (See
Equation 4 in the
Introduction. )
;
v
a)
L
O
.r)
g
t)
+r'l
-
.-troo
q
L;
F
*
H
O.
U
oo
.;
V)
E
g
q)
.'*3h9
?t
ij'
.{t7
Results ond Concfusions
l ' calculate the percent error in your determination
of the value for the
rnolar heat of fusion of ice. Your teacher
will give you the accepted value
for this quantity.
percent error
:
accepted value_
- experirnental value
accepted value
I
100 percent
I
t
-X
t
=
i
o
Heat of fusion of
lce
12q
2.
Examine the class data. Does the value obtained for the molar heat
of fusion depend on the volume of water used? Does it depend on the
mass of ice melted? Does it depend on the final temperature of the mixture?
r11
l:;
{frd-'
3.
In order to do the calculations, you assumed that all the heat lost by
the hot water was absorbed by the ice, causing it to melt. Was this
assumption correct? Explain.
4,
What assumptions were made about the temperature of the ice at the
start and finish of the experiment? Would it affect the results if these
assumptions were not correct? Explain.
;
5.
Write an equation for the melting of ice. Include the energy term in kJ
on the proper side of the equation.
O
in
I
(a
bo
=
>l
E
U
E
.2
Going Further
)r
Redesign the procedure of this experiment to improve the accuracy of z
zI
the final value for the molar heat of fusion.
d)
E
o
126
Experiment 17