The effect of different salts on ice
Hang Ha & Emma van den Berg
Dominicus college Nijmegen, The Netherlands
Summary
During the winter time, a thin layer of ice
forms itself on the roads. To melt the ice or
to prevent ice from forming on wet roads,
salt is used to spread it on the roads. This
is because salt lowers the freezing-point of
water, so the ice will melt faster and the
roads will not be so slippery anymore. A
way of testing this is when you take a salt,
for example NaCl(s), and spread it on an
ice cube, H2O(s), this ice cube will melt
quicker than an ice cube without any salt
on it. This pops up the question: how
come one salt melts ice faster than the
other salt? And you can also ask yourself
why particularly NaCl(s) is being used
instead of another kind of salt? Using an
ice cube and different kinds of solid salts,
we tested which one is the most effective
on the melting of ice.
Introduction
When you add salt to water, water
seperates the salt into ions. For example,
NaCl(s) will be separated to Na+(aq) and
Cl-(aq) ions and these are dissolved in
water. This does not mean that the
NaCl(s) has disappeared, it has only
mixed together with water. When water is
stable, it means that the processes of
melting and freezing are still going on, but
they are in balance. So you can’t see any
changing of the water, because to the
eyes it is not. If the temperature is being
lowered, the probability of a molecule to
melt is lowered. On the opposite, the
chance of a molecule to freeze becomes
higher and ice will be formed. When you
add salt to water, and the molecules of
water and salt mix together, it will take
longer for the water molecules to get back
May 2011
to ice, so the freezing rate slows down.
This means that the freezing point will be
lower when you add salt. But, what kind of
salt is best used for melting ice? Our
hypothesis is that NaCl(s) is best used to
melt ice, because it will have a great effect
on melting ice, it is readily available, and
causes no corrosion on vehicles. It doesn’t
need any special treatment or storage,
unlike other salts.
Experimental design
We have used eight measuring cylinders
and eight funnels, all identical. Then the
funnels were put on top of the cylinders.
We have also measured 2,5g from each
different kind of salt with a scale. The eight
solid salts we used were:
CaCl2
CaCO3
MgCl2
MgCO3
KCl
K2CO3
NaCl
Na2CO3
In all the eight set-ups we have put 25g of
crushed ice cubes. We have put each salt
in the funnels on top of the crushed ice
cubes, all at almost the same time, to
make sure that the measurements were
synchronic. We gathered the data by
measuring every minute the amount of
water that appeared in the funnels of each
set-up. We wrote down the measurements
in a table. We did this during 16 minutes.
This all happened at a consistent room
temperature. At the end, we compared the
results and analyzed it with our
hypothesis.
Results
Our obtained measurements show that the solid salts CaCl2 and CaCO3 melted the crushed
ice cubes the fastest. MgCO3 did almost nothing. The whole experiment took 16 minutes, so
not all the ice was melted in the end. Table 1 shows the amount of melted water (in mL) of
crushed ice cubes, treated with the different kinds of salts.
Solid
salts
(mg)
CaCl2
Time
(min.)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
2
3
4
5
6
7
7,5
8
9
9
9,5
9,75
9,8
10
10
10,25
CaCO3
0
0
0
0
0
0
0
0
0
0
0
1
2
2
2,25
2,5
3
MgCl2
0
0
3
5
6
8
9
9,5
9,5
9,75
10
10
10,25
10,5
11
11
11,25
MgCO3
0
0
0
0
0
0
0
0
0
0
0
0
0,5
0,5
0,5
0,5
0,5
KCl
0
0
0
0,5
1
1,5
1,5
2,5
3
3,5
3,5
4
4,5
4,8
4,9
5
5
K2CO3
0
0
0
2,5
3
3,75
4
4,5
4,75
4,8
4,9
5
5
5
5
5
5
NaCl
0
0
0
0
0,25
2
2,5
2,75
4,5
4,8
4,8
4,9
4,95
5
5
5
5
Na2CO3
0
0
0
0
0,25
1
1,5
2,5
2,5
2,5
3
3
4
4,4
4,5
4,6
4,8
Table 1: Amount of melted water (mL) when crushed ice cubes are treated with different
kinds of salts.
Melted water (in mL)
12
CaCl 2
10
CaCO 3
8
MgCl 2
6
MgCO 3
4
KCl
2
K2CO 3
0
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
Time (in minutes)
NaCl
Na 2 CO 3
Figure 1: Amount of melted water (in mL) of the crushed ice cubes treated with different
kinds of salts.
Discussion and conclusion
Bibliography
To measure our experiment as accurate
as possible we kept the variables
constant, the amount of salt 2,5g, the
amount of crushed ice 25g and the room
temperature 19 °C. We wrote down our
measurements at exactly the same time
(volume of the melted water). As you can
see in figure 1 there are indeed some salts
that can melt water faster than other salts.
For example, the melting process of CaCl2
started immediately while the melting
process of MgCO3 hardly takes off. How
can this happen? This will lead back to our
main inquiry question why the different
salts react differently to the melting
process (one salt rapidly starts to melt the
ice, while the other hardly reacts). To find
a conclusion of our inquiry question, you
have to take a good look at the structure of
the salts. Other questions that will pop up
are: what if you use more amounts of salt?
Will the effect be better if you mix different
salts? And if you add the salts to liquid
water and freeze the solution afterwards,
what will happen? We leave other
conditions such as impacts on the
environment, aside from our experiment.
Because by spreading salts on roads, you
corrode the vehicles. Could there be
another alternative?
http://en.wikipedia.org/wiki/Sodium_chlorid
e#Road_salt
Evaluation
Our experimental set-up was fine, the
funnels and cylinders were all of the same
content, so there would not be any
difference in reading off the volumes of the
melted ice. Maybe it was better to do the
experiment in three or four times, because
it was a bit hard for only two people to
measure every minute the volume of eight
different amounts of melted water. When
we were at the last cylinder, there has
passed a little more time as at the first
cylinder. So in the end it was better to split
the cylinders in smaller groups. We could
have improved our experiment some more
by mix some salts, or try using different
amounts of salts. Then the results would
have been more extended.
http://www.thenakedscientists.com/HTML/
content/kitchenscience/exp/melting-icewith-salt/
http://chemistry.about.com/cs/howthingsw
ork/a/aa120703a.htm
http://www.newton.dep.anl.gov/askasci/ch
em99/chem99604.htm