Melting ice with a good dissolvable salt,
a bad dissolvable salt and a reactive salt
Kan24_tim_tim
Summary of inquiry
In the winter the roads in Holland are often covered in ice, this endangers the drivers because they
can slip away easily and (might) crash. To avoid this, salt is spread out over the roads in order to keep
ice from forming and the formed ice to melt as fast as possible. We tested which salt melts the ice
fastest by laying salts with different characteristics over ice and check which one melted the ice
fastest. The outcome of our test is useful for the government to decide which salt to use. From our
tests it appeared that the dissolvable salt melts the ice the quickest.
Introduction
The goal of our experiment is to see what kind
of salt melts ice fastest. Knowing which salt
melts ice fastest is practical for the melting of
snow and ice on the roads.
Based on the fact that a good dissolvable salt
when dissolved in water, gives the water a
lower melting point, we believe that the ice
with the good dissolvable salt will melt fastest.
Unfortunately not all salts dissolve in water,
some of them do not dissolve in water and
some of them even decompose in water,
causing the initial salt to fall apart and become
other substances. The bad dissolvable and
decomposing salts will therefore not dissolve
in water, so the melting point of water stays
the same.
Method & Materials
-filter
-ice cubes, four times two ice cubes of 13
grams each
-NaCl, 0,5 grams
-Mg3(PO4)2, 2,25 grams
-(NH4)2CO3, 0,85 grams
-stopwatch
-measuring glass (100mL)
-funnels
We put the filters onto the funnels and put
the ice cubes in them. After this we carefully
dropped the different salts on the ice cubes
and started measuring the time with the
stopwatch. We also had a pair of ice cubes
with no salt on them at all. We made sure that
biggest part of the surface of the ice cube was
covered with the salt. The amount of grams of
each salt was calculated with the molar
masses of the salts so that each salt had about
the same amount of molecules on the ice
cubes. Every ten minutes we checked the
amount of water that had dropped into the
measuring glass and noted it for each salt until
all the ice had melted, when an ice cube was
almost melted we watched so we knew
exactly the time it was completely melted.
Results
The amount of water that was melted and had
gone through the filter into the measuring
glass is shown as a function of the time in
table 1.
Figure 1
30
Tabel 1
Mg3(PO4)2
(NH4)2CO3
0
0
0
No
salt
0
1 mL
0 mL
1 mL
0 mL
4 mL
1 mL
4 mL
2 mL
12
mL
18
mL
21
mL
23
mL
28
mL
5 mL
11 mL
6 mL
25
20
Formed water
15
(mL)
10
5
0
NaCl
10 mL
18 mL
16 mL
21 mL
11
mL
15
mL
19
mL
23
mL
19 mL
22 mL
24 mL
25,5 mL
28
mL
25 mL
26 mL
24
mL
28
mL
26 mL
26 mL
24,5
mL
28
mL
26 mL
26 mL
26
mL
Tabel 1: Melted water in function of time.
The different salts we used are stated in the top row,
underneath that the amount of water that has melted into the
measuring glass is stated after periods of 10 minutes.
Mg3(PO4)2
(NH4)2CO3
0 min
10 min
20 min
30 min
40 min
50 min
60 min
1h 12 min
1h 14 min
1h 17 min
1h 20 min
0
min
10
min
20
min
30
min
40
min
50
min
60
min
1h
12
min
1h
14
min
1h
17
min
1h
20
min
NaCl
No Salt
Time
Figure 1: Formed water in function of time, graph.
On the Y-axes is the formed water from the different salts in
mL.
On the X-axes is the time it took to form this amount of water in
the measuring glass.
Conclusion & Discussion
The ice melted fastest with the good
dissolvable salt on its surface, our hypothesis
was correct. We have come up with 3 theories
why the good dissolvable salt melts the ice so
fast.
Theory 1. Dissolvable salts are known for,
when dissolved in water, lowering the melting
point of the water. The salt could have the
same effect on the ice, lowering its melting
point and therefore speeding up the melting
process.
Theory 2. Another characteristic of salts is that
they absorb water. When the ice cube with
the salt on it melts, the liquid water that is
formed will be absorbed by the salt, making it
impossible for the formed water to evaporate.
Evaporation of water costs energy and
therefore heat. This heat is now not spilled on
the evaporation and so the melting process is
speeded up.
Theory 3. Water molecules are polar. Salts are
electrically charged , so the water will be
attracted by the salt because of the difference
in electrical charge. Because of this attraction
the water molecules in the salt that are
already a little bit melted are sucked out of
the ice because of the difference of the
molecules in charge. Giving it more surface
area in the ice for the outer temperature to
melt it faster.
These theories are ordered in the likeliness of
the event actually happening.
The salt that decomposes in water was the
second fastest in melting the ice. The
decomposing salt decomposes into NH3, CO2
and H2O. The first 2 are gases and the water is
liquid. We think that in the beginning on the
ice it had the same effect as the good
dissolvable salt because there wasn’t enough
liquid water to make it decompose, after the
ice had melted a little, it decomposed and the
ice melted just like normal ice, but because
the salt had made gaps in the surface of the
ice cube there was more surface area for the
outer temperature to melt the ice.
The bad dissolvable ice didn’t do much accept
absorbing some of the water formed, which
might make it easier for the ice to melt.
However the bad dissolvable ice might have
also worked a bit against the melting process
for it isolated the ice keeping the ice from
warming up by the surrounding temperature.
Noticeable was that we got 26 mL of water
from every set up and from the NaCl even 28
mL of filtrate while initially we had put 25 mL
of water in the ice used in the set up. To
explain this we think that we might have
measured the amount of water we put into
the ice cubes wrong, or there had formed
some extra ice on top of the ice cubes in the
freezer, or the salt that had gone through the
filter with the melted water had given the
filtrate some extra volume.
What was also interesting was that during the
blanco test it did not take much longer for the
ice to completely melt than with a salt added.
This can be explained as follows. As you can
see in our results, in the beginning of the
melting process the ice with the decomposing
or dissolving salt had melted a lot more than
the ice in the blanco test. It was only in the
end that the blanco test came closer to the
other set ups. This could be so because the
water that had melted away in the tests with
salts had some salt dissolved in it and
therefore there was less salt on the ice to
uphold the fast melting process. In the case of
the decomposing salt, some of the salt had
decomposed after a period of time also
leaving less salt to melt the water faster.
Sources
BINAS