10/4/2011
SCHEIKUNDE
EFFECTIVENESS OF SODIUMCHLORIDE
Thien Nguyen & Koshar Safaipour |5W
Effectiveness of Salt
Nguyen T, Safaipour K.
Willem de Zwijger College Papendrecht, The Netherlands
Summary
Road salt has saved many lives and it will continue saving lives. The only
problem nowadays is that the Road salt sometimes isn’t suitable for the current
temperature. There is second problem as well. Since there is a shortage of road
salt, we mustn’t overuse it, so, we have to find the exact amount of salt which is
needed for the exact temperature. In that order we wont waste anymore of our
precious, life’s saving road salt.
___________________________________________________________
Introduction
NaCl can lower the freezing point of
the water. So our question is: how
many gram of NaCl do we need to
lower the freezing point of water with
-1.0 °C and what is the minimum
freezing point which we can reach of
water. We expect that the lowest
freezing point is 21˚C as we found
that on an internet site. The
maximum of NaCl per kg water is
358,5grams so we think a higher
amount of NaCl should not have any
effect anymore due to the fact that
the solution is saturated. Also we
expect a diminishing effectiveness of
the salt (a small amount which has a
stronger effect relatively than a large
amount of NaCl). We are going to
determine the average NaCl needed
for a ∆-1.0 °C. After that, we can
calculate how much salt there is
needed for the -1,0 temperature
drop which we desire.
Experimental procedure and
approach
We took 9 identical tubes. All of them
containing the same amount of water
(100mL). Then we filled 8 of them
with a variable amount of NaCl
(amounts were between 5gram and
40gram with a ∆5gram, measured
with a scale).
All of the 8 tubes with solution and 1
tube with only water as control were
placed in a refrigerator with
temperature control. We lowered the
temperature by 1˚C every X-minutes
till the solution was the same
temperature as the refrigerator
indicated (X-minutes due to the fact
that the different solutions froze in
different amount of minutes). Then
with a thermometer we measured
the temperature of all the solutions
to be sure they were the same
temperature as the refrigerator
indicator. The whole procedure was
done twice as control.
Data gathering and analysis
Every 10 minutes we checked the
temperature of the solutions with the
thermometers. If it wasn’t the same
as the refrigerator indicated then we
waited a bit longer. Checking which
solution was frozen, we noted the
temperature which went along with
it. We did this till every tube was
frozen and repeated this for check
up. On that basis we made a chart
which helps us to see the connection.
Results
Table 1 presents the solutions
(concentrations of NaCL in water)
and the temperature which was
needed to freeze the solutions.
Amount of
T in
T in
NaCL in
Celsius Celsius
100mL water Exp. 1
Exp. 2
0 gram
0
0
5 gram
-3
-4
10 gram
-7
-7
15 gram
-10
-10
20 gram
-13
-12
25 gram
-16
-15
30 gram
-19
-19
35 gram
-22
-21
40 gram
-22
-21
Table 1: Temperature needed to
freeze the solution.
Figure 1 shows the temperature
needed for a specific solution of NaCL
in water.
Figure 1: Average Temperature
needed to freeze solution.
Conclusion and discussion
Looking critically at our experimental
procedure and approach we see that
in the set of experiments we kept the
same variables constant: The
amount of water in the solution, the
tube the solution was in and of
course the placement of the tubes in
the refrigerator.
As shown in Figure 1 ∆gram of NaCL
is directly proportional with the
∆temperature of freezing. We were
stunned by these results. This
phenomenon wasn’t expected but
after putting research in it we found
out that the freezing point reduces
linear with the amount of molecules
that are present in the solution (not
only for NaCl but every kind of salt!).
We came to the second conclusion
that the lowest freezing point of a
solution with NaCl was indeed
somewhere around 22˚C. Even after
increasing the amount NaCl further
to more than the water could contain
(>35,85gram NaCL per 100mL
water), it still froze on 22˚C.
Because of the fact that the results
were linear, we could calculate the
∆grams NaCl for a ∆-1,0˚C freezing
point drop.
∆35grams/∆22˚C= ±1,6. So for
every ∆-1,0˚C there is 1,6 grams
needed (on a base of 100mL water).
Between experiment 1 and 2 there
were slightly differences, this
because our refrigerator could only
have a ∆1,0˚C and not a ∆0,1˚C
which made it a bit less accurate.
Bibliography
1.http://www.zoutman.com/nl/infor
matie/wegenzout
2.http://nl.wikipedia.org/wiki/Strooiz
out