‘To melt, or not to melt’
Nienke van Putten and Elise Prins
K.S.G. De Breul, The Netherlands
Submission Date: 15-03-2011
Summary
To make icy roads passable, the highway personnel spreads every winter salt over these roads. Even
though NaCl (sodium chloride), from which the biggest part of the current road salt consists, seems to be
available in unlimited supply, there’s every winter a shortage of the current road salt in the Netherlands.
This raises the question of there are alternatives that are easier to get, and even as productive as the
current road salt. But it also raised further questions such as are ‘green’ alternatives possible to avoid
corrosion on the nature. Using an experimental design with ice and 5 different kinds of salts, we’ve
investigated some alternatives.
Introduction
Every winter the government spreads tons of
NaCl on our roads, but what impact does that
have on the adjacent nature?
The nature will not only be polluted by the salt
water (which forms by melting of the road ice),
but the trees are also sprayed with the salt
solution when cars are passing by. Animals
also have troubles with finding drinking water,
because the concentration of salts increases in
the environmental water. That’s why it’s so
important to look for green alternatives for
the current road salt.
Salt lowers the freezing point of water. The
freezing point of the solution is lower than
that of water itself. When you bring the salt in
contact with the ice, the salt splits into
separated ions. NaCl splits into Na+-ions and
Cl- -ions.
NaCl(aq)  Na+(aq) + Cl- (aq)
You see that one mole of NaCl produces two
moles of ions, and therefore a double
lowering of the freezing point. Salts such as
CaCl2 produce three moles of ions, so that salt
will increase the lowering of the freezing point
even more.
Our inquiry question is: ‘Are there alternatives
for NaCl which are even as productive as NaCl,
but better for the environment?’
Our hypothesis is that there are alternatives
for the current NaCl, but they are possibly
harder to get or more expensive.
Experimental design
We took six identical measuring cylinders and
six identical funnels. The funnels were put on
top of the measuring cylinders. The first
funnel was filled with 50 g. crushed ice cubes
and in the other five set-ups each funnel got
also 5,0 g. of a salt. In every of these last five
funnels we used a different salt, we used: NaCl
(sodium chloride) (s), NH4Cl
(ammoniumchloride or salmiac)(s), CaCl2
(calcium chloride)(s), CH3COONa (sodium
acetate) (s) and Ca(CH3COO)2 (calcium acetate)
(s).
When the ice started to melt, the melting
water flowed into the measuring cylinder, so
we measured the volume in mL of this water
after five and ten minutes.
Figure 1: Experimental set-up
5 min.
10 min.
stdev.
H2O (s) or ice
5,8 ml
8,2 ml
3,342
Ice + NaCl
10,8 ml
13,0 ml
1,414
Ice + NH4Cl
10,3 ml
13,7 ml
2,867
Ice + CaCl2
16,7 ml
19,2 ml
3,009
Ice + CH3COONa
11,3 ml
13,5 ml
3,082
Ice + Ca(CH3COO)2
9,5 ml
12,8 ml
2,953
Time
Measured
Table 1: Average amount of water (mL) released when
crushed ice is treated with and without the different
salts. The standard deviations are given in the third
column.
As you can see in Figure 2 and Table 1, there
was less melted water in the measuring
cylinder of the set-up without a salt (average
of 8,2 mL in 10 minutes) than in the set-ups
with the salts (average of 14,4 mL).
→Volume of melted ice (mL)
Results
We compared the results from the four
alternatives with those from the current road
salt.
We observed that the ice with the salt, was at
the end one big clot and wasn´t clear anymore.
Meanwhile, the ice without the salt was still
divided in pieces, and was clear. This can be
explained because of the hygroscopic feature
of the salts: The salts attract the water
molecules of the ice and this causes the
clotting.
As you can see in Table 1 and Figure 2, the setup with the ice and CaCl2 had the most
melting water. Especially in the beginning:
There was more ice melted in the first 5
minutes than in the other five set-ups in 10
minutes.
25
20
15
10
5
after 5 min.
0
after 10 min.
→ Composition of the ice- salt mixture
Figure 2: Average amount of melted ice (in mL) from
crushed ice in the six set-ups
Green alternatives
We also looked at the impact of the salts for
the natural environment. We took the salts
which can compete with Sodium Chloride. We
first investigated the salts with the greatest
impact on the melting temperature (the
greatest volume of melted ice).
Below we present a review with candidate
salts, beginning from the salt with the
strongest action, CaCl2, till the salt with the
weakest action, NaCl. We omitted
Ca(CH3COO)2, because this salt had less or
comparable melting water than that from the
current road salt, so it seemed to be no good
alternative.
CaCl2 (Calcium chloride):
+ Very cheap and easy to get
+ Produces heat when dissolving into the ice,
so it’s very effective (especially at
temperatures below 0 °C or in severe
conditions)
+ Fast-acting
- More toxic for plants and human than
sodium chloride
- Little contribution to the raise of chloride
concentration in the environmental water.
NH4Cl (Ammonium chloride/Salmiac)
+Easy to get
- You have to store it without any moisture
- Irritating for the eyes and lungs
CH3COONa (Sodium acetate)
+ It’s very cheap
- Other salts and a lot of chemic reactions
needed to produce it
- It has an unpleasant light smell of acetic acid
NaCl (Sodium chloride)
+ You can produce it in many different ways
- It’s dangerous for the eyes
- Little contribution for the raise of chloride in
the water
Discussion
Looking critically at our inquiry, there are
some things that could be done better.
Unfortunately a window was opened, so the
temperature in the room went down. That’s
why we had some fluctuations in the
temperature.
When we put the ice in the funnels, the ice
was already a little bit melted. But this varied,
so some set-ups began with 5 ml. melted ice
and some with 1 mL. So we couldn’t keep it
constant. We tried to crunch the ice as fast as
possible, but every time a little bit was melted,
so we did every measure three times (in triple).
Another problem was that when we put the
salt on the ice, every time a little bit salt was
left in the little bowl. So not all the salt could
be spread over the ice.
It was also difficult to spread the salt equally
over the ice, so some parts of the ice in the
funnel had less salt than other parts.
The moment that we started our stopwatch
was a little bit inconstant, but this is only one
or two seconds, so that does not have
substantial influences on our results.
Conclusion
There are alternatives for the current ice road
salt. There are three salts which had better
melting action on the ice than NaCl, but the
results were the best with CaCl2. CH3COONa
could also be used, but this salt hasn’t got
much better results than NaCl.
CaCl2 is cheap and easy to get, just like NaCl,
and íf you treat it adequate, it’s not more
dangerous than NaCl.
Evaluation
We kept a few variables constant: The amount
of salt, the amount of ice, the time in which
we observed the melting ice, and we tried to
keep the temperature constant in the room.
We measured the volume of the melting
ice(our dependent variable).
Suggestions for improvement:
-
-
A faster solution for crunching the ice or
use ice which is already in smaller pieces.
To work with the number of moles of the
salts, instead of grams. In this experiment
we only looked at the amount of grams,
resulting in different amounts of moles
used.
To do every measure more times, for
example 4 of 5 times each, because our
standard deviations were quite big.
Further inquiry questions:
-
-
What will the effect of more salt be?
Is there more ice melting possible by
mixing two salts together?
What influence have the cars by riding on
top of the road salt?
How is the melting process on a real road
with asphalt? Because then the water
doesn’t sink down like in our inquiry, but it
remains on the road.
To investigate the working of road salts in
a low temperature instead of room
temperature.
-
-
Are there alternatives for the current
surface, like asphalt which absorbs more
solar radiation, so there’s more heat
available to melt the ice?
What’s the influence of the alternative on
the pH of the soil and the environmental
water?
Bibliography
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‘The effect of NaCl(s) on ice’, Iru, P.,
Luib, A., & Nelem, D., Journal of
Anorgano Chemistry, Oktober 2010.
http://www.zout.be/winter/dossierstr
ooizout4.html
http://www.assinkchemie.nl/msds/X2
01121.htm
http://www.pieternieuwland.nl/Menu
_Items/Projecten/Symposium/sympos
ium20102011/organisatie/organisatie.htm
http://edepot.wur.nl/132660