CHEMISTRY :
BREAKING THE ICE
Authors:
Furkan Yildirim
Bugrahan Gedik
Submission Date:
April 5th 2010
Summary
Salt is widely known for melting ice when
it’s needed. For instance, the freezing cold
during winter times creates slippery roads
and pavements unable to walk on, which
is helped by using salt to make the ice
thaw.
Sodium chloride (NaCl(s)) is known to be
used for this application, and is actually
the only salt ever getting mention ed and
used. It raises the question: Is NaCl(s) the
best salt to make ice melt faster? Are
there alternatives. We found that sodium
acetate (CH3COONa(s)) makes a bigger
amount of ice melt than ‘the usual salt’
NaCl.
Introduction
It is a well-known fact that salts lower the
freezing point of water. That’s why we use
NaCl(s) to prevent ice from forming in
freezing weather. For example, when one
mole of sugar is dissolved in 1 L water, the
freezing point of water is lowered by 1.86°
C. This value is called the freezing-point
depression constant (Kf). The freezingpoint depression constant depends on the
solvent. We know that one mole of NaCl(s)
(58.5g) in 1 L of water doubles the drop in
freezing point. Because, when NaCl(s)
dissolves in water, it produces a Na+ and a
Cl- ion. Both of the ions contribute
independently to the lowering of the
freezing point of water.
But what about the salt sodium acetate
(CH3COONa)? We know that it has a
molecular mass of 82,03379 g/mol. But we
do not know the freezing-point depression
constant of it. So we do not know its effect
on the melting of ice. That bears the
questions:
-
What is the difference between
the effect of sodiumacetate and
NaCl(s) on the melting of ice? Is
one of them more effective than
the other?
Our hypothesis is that at the beginning the
smelting process of the ice with will start
slowly, because there’s no water at the
beginning. But because of the hygroscopic
feature of both the substances a little
surface of water on the ice will soon be
formed and speed up the melting process.
But the melting process of the ice with
NaCl will be faster.
Experimental design
How could we execute this experiment as
good as possible? To reach the answer of
that question, we have to look at what we
want to measure. In order to know how
well the effect of each salt is on the
melting process, we will need to measure
the consequence of that process: The
quantity of melted ice, and the time it
took to melt. This can be measured with
the following set-up:
-
Two measuring cylinders for each
ice cube and salt.
A folded coffee filter in each
cylinder, where the ice cubes are
layed.
We measured the amount of melted ice,
that is mL of water, and the time (by a
stopwatch).
The results
We didn’t wait till the crushed ice melted, but measured the amount of water that was
released for half an hour.
Time (in minutes)
With CH3COONa (ml)
With NaCl (ml)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
13
13.5
14
14.5
15
15.5
16
16.5
17
17.5
18
18.5
19
19.5
20
20.5
21
21.5
0
3.5
4.0
4.6
5.0
5.2
5.4
5.6
5.9
5.9
6.0
6.0
6.2
6.3
6.4
6.6
6.8
6.9
7.0
7.2
7.3
7.4
7.6
7.8
8.0
8.2
8.4
8.6
8.8
9.0
9.2
9.6
9.6
9.6
9.8
10.0
10.0
10.3
10.4
10.6
10.8
11.0
11.2
11.3
0
2.9
3.2
3.5
4.0
4.2
4.4
4.6
4.6
4.8
4.8
5.0
5.0
5.1
5.2
5.2
5.2
5.2
5.2
5.3
5.3
5.4
5.4
5.4
5.5
5.5
5.6
5.8
6.0
6.2
6.3
6.4
6.4
6.4
6.4
6.5
6.5
6.6
6.7
6.8
6.9
7.0
7.2
7.2
22
22.5
23
23.5
24
24.5
25
25.5
26
26.5
27
27.5
28
28.5
29
29.5
30
11.6
11.6
11.8
12.0
12.3
12.6
12.7
12.8
12.9
13.0
13.3
13.4
13.6
13.8
13.9
14.0
14.3
7.4
7.4
7.5
7.6
7.6
7.7
7.7
7.8
7.8
7.9
8.0
8.1
8.2
8.4
8.4
8.7
8.9
16
14
Melted Water (ml)
12
10
8
CH3COONa
6
NaCl
4
2
0
0
2.5
5
7.5
10
12.5
15
17.5
Time (in minutes)
20
22.5
25
27.5
30
Conclusion
Through looking at the observations, we
can see that sodium acetate has a better
effect on the melting process of ice.
With an experiment in which the control
variables (room temperature, volume ice
cubes, molar amount of each salt) were
kept constant, the outcome is somewhat
reliable. Sodium acetate fastens the
process greatly, and makes an amount of
ice melt twice the amount NaCl(s) does.
This makes the reason for the apparent
monopoly of sodium chloride in the use of
melting the ice on the roads during
freezing times questionable.
Discussion
At our experiment we kept all the same
variables constant: the amount of crushed
ice, the room temperature and the time
tame taken. We measured the same
dependent variable: the volume of the
melted water. But not everything went
perfectly right. We have some things that
may can influence our results:
-
-
When we added the salts, we
observed that the melting process
were proceeding very fast. Because
of that, the first few result we have
noted, may not be accurate as the
other results.
When we added the salts on the
crushed ice, we didn’t have spread
it equally on the crushed ice. That
may have caused that at some
places of the crushed ice the
smelting process had been started
earlier. Or that at some places,
where there was a little of the salt,
-
-
the smelt process had been started
later.
We had comparatively much more
gram CH3COONa than NaCl. The
extra weight of CH3COONa might
have caused a extra pressure
which can have caused that the ice
smelt faster.
We did the experiment only twice,
so it may not be a very accurate
experiment.
Evaluation
If we take a good look at the way we
experimented, there is a lot which could
be done better. For instance the quantity
of experiments we did. We executed the
experiment only twice, which actually is
not enough to rely on the results.
Further we think it would have been
interesting to have looked at the features
of each salt to figure out what the causes
of the difference are.
Also, why is NaCl(s) preferred in use, while
sodium acetate appears to be much more
effective?
All in all this experiment has lead to an
interesting additional inquiry question
which will be answered in the future.