The effect of different chloride salts on melting time of ice
Mitchell Seraus & Sergío Muyden
Pieter Nieuwland College, the Netherlands
Received April 13, 2011
Summary
Nowadays spreading NaCl(s) on the roads is the most common way of defrosting icy roads.
The government invests a lot of money in doing that. But unfortunately sometimes salt runs
out too quickly, and when that happens the roads will stay frozen. Because of this we have to
find new ways for defrosting icy roads without having the problem of it running out. The
solution to this may be as simple as using different types of salts. In order to test this out, we
used four different chloride salts (KCl, NaCl, MgCl2, CaCl2) to test how quickly the ice melts.
The results were that MgCl2 and CaCl2 were the most effective salts. Yet this raised the
question why these two salts were the most effective.
Road salts, Melting time, MgCl2, CaCl2
Introduction
Salt is a melting agent, and is therefore
commonly used for defrosting icy roads.
When dissolving salts in water, the
freezing point lowers and thus it is more
difficult to freeze the water.
This phenomenon is called freezing-point
depression. This phenomenon can be
noticed in sea water, which remains liquid
at temperatures below 0 degrees Celsius.
The freezing-point depression depends on
the molar mass of a chemical substance,
and not on the kind of chemical substance.
The formula for calculating the freezingpoint depression is: T  K  m  i .
The T stands for the freezing-point
depressing (in K or °C). The K stands for
the cryoscopic constant, which is
dependent on the properties of the solvent,
not the solute (in K · kg/mol). The m is the
molarity (mol solute per kg of solvent).
The i is the van 't Hoff factor (number of
solute particles per mole). The number of
particles in the salt-ion has an effect on
how fast the ice melts e.g. if you have
twice as much particles dissolved in ice
than
normally,
the
freezing-point
depression will also be twice as high. This
raises the question: what is the connection
between the melting time of ice and
different types of chloride salts? Our
hypothesis is that the salts which contain
the most particles will have the most effect
on the melting time of ice.
Experimental procedure and approach
We took four identical measuring cups and
we put one ice cube in each measuring cup.
The ice cubes were equally sized.
We poured 10.0 grams of NaCl(s) on the
first ice cube, 10.0 grams of MgCl2(s) on
the second, 10.0 grams of KCl(s) on the
third and on the fourth we poured 10.0
grams of CaCl2(s). We also stirred it a
little, every 10 minutes. We did this twice
to make sure we had an as accurate as
possible result.
Figure 1: Experimental setup of the inquiry
Data gathering and analysis
We immediately began measuring how
long it took for the ice cubes to melt
completely. The results were averaged and
put in a graph. Then we analyzed the graph
to get a clearer image of the results.
Results
The results varied a lot. Some types of
chloride salts were remarkably more
effective than others. It also seemed like in
the beginning the ice was melting faster
than at the end. The results of table 1 are
averaged.
Time(in
minutes
and
seconds)
With
NaCl
45:50
With
KCl
48:40
With
CaCl2
31:12
With
MgCl2
41:59
Table 1: Melting time of ice with different types of
chloride salts.
Time (in minutes)
Figure 2 shows the averaged time it took
for the ice cubes to melt completely, with
different types of chloride salts.
60
50
40
30
20
10
0
NaCl
KCl
CaCl2
accelerate the melting process. The
phenomenon that MgCl2(s) and CaCl2(s)
melt much faster can also be explained.
The most obvious explanation is that
MgCl2(s) and CaCl2(s) contain more
particles per mole than KCl(s) and NaCl(s)
(van 't Hoff factor: i), so they have more
particles to dissolve.
Furthermore the difference between the
melting time of MgCl2(s) and CaCl2(s),
KCl(s) and NaCl(s) could also be
explained.
The explanation for this is that CaCl2(s)
penetrates ice faster than MgCl2(s). So, it
dissolves faster in the ice and therefore
melts the ice faster.
The explanation for the difference between
the results of KCl(s) and NaCl(s) is the
same; NaCl(s) penetrates ice faster than
KCl(s). This raises further questions for the
inquiry: what are the effects of MgCl2(s)
and CaCl2(s) on the natural environment?
What are the effects of MgCl2(s) and
CaCl2(s) on cars and bikes? What are the
effects of MgCl2(s) and CaCl2(s) on human
health? Why aren’t they using MgCl2(s)
and CaCl2(s) for melting ice in the winter?
What are the long-term effects on the
asphalt?
MgCl2
Figure 2: Melting time of ice (in minutes) with
different types of chloride salts.
Conclusion and discussion
Looking at our procedures we see that we
kept the control variables constant: the
amount of (sun)light, the temperature, the
size of the ice cubes, the stirring and the
amount of salt. We measured the
dependent variable (melting time). Also
looking at our results we can see that ice
with KCl(s) melted more slowly than with
the other salts, whereas ice with CaCl2(s)
melted very fast.
The NaCl(s) and MgCl2(s) stayed in the
middle of the two. In the beginning of the
experiment, the ice cubes seemed to melt
faster than at the end. An explanation for
this could be that almost all the salt is than
dissolved and that more salt is needed to
Evaluation
Looking critically at the experimental setup, we think that we handled everything
very well. We kept all the control variables
constant. Nevertheless it took a lot of time
to do the experiment properly.
What we have to do different next time is
that we should crush the ice first and then
pour the salt over it. Furthermore it’s also
better to do every measuring at the same
time. Those simple adjustments would
save a lot of time.
Further inquiry questions could be: what
are the effects of MgCl2(s) and CaCl2(s) on
the natural environment? What are the
effects of MgCl2(s) and CaCl2(s) on cars
and bikes. What are the effects of MgCl2(s)
and CaCl2(s) on human health? What are
the long-term effects on the asphalt?
Because maybe there is a reason for not
using MgCl2(s) and CaCl2(s) instead of
KCl(s) and NaCl(s) on frozen roads and by
finding that reason you could do more
investigation about the effects of MgCl2(s)
and CaCl2(s) on ice.
Bibliography
1. http://chemistry.about.com/cs/howthin
gswork/a/aa120703a.htm
2. http://pollard.mnsi.net/calvsmag.html
3. http://en.wikipedia.org/wiki/Freezingpoint_depression
4. NVON-commissie, 2004, Binas,
Groningen. Wolters-Noordhoff