The rusty effects of road salt
By: Hanna Bentz van den Berg and Gert-Jan van den Eijnden
Gemeentelijk gymnasium Hilversum, The Netherlands
Summary
In the winter times when there is ice on the road it’s slippery. To avoid dangerous situations
in Holland we pour about hundred thousand tons of road salt a year on the roads to make
the roads clear from ice. The salt will dissolve in the water and the freezing point of this
solution is lower than the freezing point of water, so the roads remain clear from ice earlier.
But road salt has also a bad side. It will corrode with the iron parts of your vehicle. The salt
starts a redoxreaction with the iron in an environment of water and oxygen. It’s an
interesting question how you could avoid the corrosion and keep the roads safe at the same
time.
Introduction
The main salt that is used as road salt is A redoxreaction is normally split into two
NaCl, but there are alternatives. As an parts, the reduction and the oxidation. In
example airports use urea as road salt the reduction electrons are released by
because this would corrode less with the the redactors and in the oxidation
iron parts on the plane. We wondered if electrons are received by the oxidiser.
the differences in corrosion between Urea
and road salt is really that big. We also Reduction
wondered if a composed salt is a solution An iron atom, redactor, splits off two
to avoid damage on your vehicle due to electrons and transform into an iron ion.
corrosion.
Fe(s) → Fe2+(aq) + 2 e−
Theoretical assumptions
The product of the corrosion process of Oxidation
the element iron is called rust. This is the The oxidisers, O2 and H2O, receive the
result of this series of electrochemical electrons that were released by the
reactions in which iron oxide or Fe(OH)3 is redactors and in this case form hydroxide
formed. When an electrochemical ions.
reaction occurs electrons are transferred
from the redactor (negative pole) to the O2(g) + 4 e- + 2H2O(l) → 4 OH-(aq)
oxidiser (positive pole) and a electrical
circuit is formed. Electrons need a closed These two reactions together have to be
electrical circuit to travel from the neutral, so al the electrons that are
negative pole to the positive pole. This is released have to be received by oxidisers.
where the road salt comes in. Salts consist
of ions, positive and negatively charged Fe(s) → Fe2+(aq) + 2 e− X2
particles. These ions help close the O2(g) + 4 e- + 2H2O(l) → 4 OH-(aq)
electrical circuit by transporting electrons
form the redactor (Fe) to the oxidiser (O2). When we take those two reaction and put
This way the redoxreactions take place them together we find the total reaction.
more easily.
2Fe(s) + O2(g) + 2H2O(l) → placed a lit on top of each dish. We left
2Fe2+(aq) + 4 OH-(aq) the dishes in an environment with
constant temperature and humidity for
When the two results of the total react two weeks. After one week we picked off
with each other Fe(OH)2 is formed. all the lids so the water could evaporate.
After another week all the water was gone
Fe2+ (aq) + 2 OH- (aq) → Fe(OH)2 (s) and the corroded piece of iron that had
reacted with the salt was left. Now we
Fe(OH)2 reacts with water and forms weighed all the dishes to see how much
Fe(OH)3 a.k.a. rust. weight had been added. Dish number with
particular salt:
2Fe(OH)2 + H2O (l) → 2Fe(OH)3 (s) + O2(g) 1 = NaCl
2 = NaCl
Inquiry question 3 = Glucose (C6H12O6)
In our experiment we asked ourselves the 4 = Glucose (C6H12O6)
question: “What is the effect of the 5 = MgCl2
different salt and organic chemicals on the 6 = MgCl2
corrosion of Iron?” 7 = Urea (CH4N2O)
8 = Urea (CH4N2O)
Hypothesis
Our hypothesis is that the salts will have a
much bigger effect on the corrosion speed
than the organic chemicals. This will be
because salts fall apart in ions and organic
particles remain intact. With these ions
the corrosion of iron will be more quickly,
because they close the gapes in the
electrical circuit. Complex salts will do
more damage than simple salts because
they release more ions and the extra ions
close the gapes in the electrical circuit
more easily.
Experimental procedure and approach
We took eight Petri dishes and filled them
with different kinds of salt (NaCl, Glucose,
MgCl and Ur) with a concentration of one
Molar of each salt. We did every
experiment twice, so there is less change
we make a measurement error. We
calculated how much of every salt we
needed to have a concentration of one
Molar from every salt in each petridish.
Then we putted a piece of iron in each
dish. We weighed the dishes with the right
amount of salt and the piece of iron in it.
At last we completed them with water and
Results Average difference in weight
After a week the petridish covers ware
0,2
removed. An other week later, when the 0,18
water was evaporated, we came back and 0,16
weight difference (g)
0,14
weighted each petridish for the second 0,12
time. We were looking for a difference in 0,1
0,08
weight. Because the Fe2+ions react with 0,06
OH-ions Fe(OH)2molecules are formed 0,04
0,02
these weight more than the Fe ions, this 0
NaCl C6H12O6 MgCl2 CH4N2O
results in a difference in weight is caused
by the of OH-ions. If there is more Diagram 1: Average difference in weight
difference in weight, more rust has
formed. In our experiment we measured Conclusion, discussion and evaluation
the following results. Looking at the results we are able to conclude
that complex salt do accelerate the corrosion
process and that our hypothesis isn’t
Petridish weight weight difference
completely right. However, there is one
Petri dish Petri dish in weight problem, the NaCl didn’t have as much effect
before after before - on the iron as we expected.
experiment experiment after (gram)
(gram) (gram) Our unexpected measurements may be
1 54,27 54,30 0,03 caused by irregularities or false readings. We
2 53,54 53,53 -0,01 tried to expel all irregularities by keeping
control variables, temperature, quantity and
3 54,06 54,05 -0,01
concentration constant. We also weighted the
4 54,77 54,80 0,03 dishes as accurate as possible (with two
5 53,14 53,34 0,19 decimals). The deviation in our results is
6 55,67 55,86 0,19 bigger than 0,5% and therefore are our results
not reliable enough to make an exact
7 56,41 56,40 -0,01
conclusion. For more exact measurements we
8 54,04 54,04 0,00 have to do some more testing. We could also
Table 1: Difference in weight be more sure that all the water has
evaporated because this could make big
difference in our measurements. And we
added chemical average difference in have to ask ourselves the question, “why is
weight (gram) the weight difference less than we expected in
the dish with NaCl-solvent”. We think this may
NaCl 0,01
be because the ion concentration was not
C6H12O6 0,01 high enough to fill the gapes in the electrical
MgCl2 0,19 circuit. Therefore the redoxreaction couldn’t
CH4N2O 0,00 take place.
Table 2: Average difference in weight
This experiment raised the question, Are
there more side effects? Has road salt a
bad influence on the flora and fauna next
to the road? And does it have any
consequences for the road surface? Do
tiers suffer from brine?
Bibliography
http://nl.wikipedia.org/wiki/Roest_%28m
etaal%29
http://en.wikipedia.org/wiki/Urea
http://en.wikipedia.org/wiki/Electric_circu
it
http://en.wikipedia.org/wiki/Redox
www.pieternieuwland.nl