TCE Contamination and Cleanup Curriculum
Oxidation of TCE with Potassium
Permanganate
Written by Christopher Martin
Editor: Stephanie Nardei
Time:
2 class period
Preparation
1 hour to make solutions
Time:
Materials:
Acidified ferrous sulfate 0.0025M
FeSO4·7H2O (0.7g /1000 ml.) + 25ml. of 2M H2SO4
Potassium permanganate 0.01M
KMnO4 (0.4g per 250ml)
Abstract
Students consider the threat posed by TCE in
the ground water. They learn how TCE is
removed by treating the water with potassium
permanganate. Students learn how electron
transfer takes place in this oxidation/ reduction
reaction.
Objectives
Students will be able to explain how:
 TCE contamination of the groundwater
is treated
 Balance redox (reduction/ oxidation
reactions.
National Science Education
Standards:
The Designed World
B. Materials and Manufacturing
Waste management includes considerations of
quantity, safety, degradability, and cost. It
requires social and technological innovations,
because waste-disposal problems are political
and economic as well as technical.
Arizona Science Standards
Strand5
Physical Science
TCE Contamination and Cleanup Curriculum
Concept 4: Chemical Reactions; Investigate relationships between reactants and products in
chemical reactions.
PO.13
Determine the transfer of electrons in oxidation/reduction reactions.
gical innovations, because waste-disposal problems are political and economic as well as
technical
Teacher Background
Chlorinated ethylenes, especially trichloroethylene (TCE) and tetrachloroethylene (PCE), are
some of the most frequently detected groundwater contaminants in the US, especially in Tucson,
and have been identified as priority pollutants by the EPA. Oxidation of chlorinated ethylenes
using potassium permanganate has been demonstrated to be a rapid and effective technique for
remediation. As with other degradation processes affecting these contaminants, stable isotope
analysis has the potential to qualify and/or quantify the efficacy of permanganate oxidation as a
remediation technique.
Many contaminants in groundwater can be treated using redox reactions. Redox (oxidation and
reduction) is a natural process and often used in chemistry.
Related and Resource Websites
Chemical Oxidation In Depth: Potassium Permanganate Oxidation
http://www.terratechnik.ca/Current-Environmental-Issues-Articles/potassium-permanganate.html
EPA EIMS Metadata Report – Document
http://oaspub.epa.gov/eims/eimsapi.dispdetail?deid=23249
Reduction and Oxidation Reactions http://www.chemtutor.com/redox.htm
Activity

Introduce the lesson by reviewing the health risks associated with Trichloroethylene
(TCE). Students will consider this description from the EPA:

TCE exposure is associated with several adverse health effects, including neurotoxicity,
immunotoxicity, developmental toxicity, liver toxicity, kidney toxicity, endocrine effects,
and several forms of cancer. Mechanistic research indicates that TCE-induced
carcinogenesis is complex, involving multiple carcinogenic metabolites acting through
multiple modes of action. Under EPA's proposed (1996, 1999) cancer guidelines, TCE
can be characterized as "highly likely to produce cancer in humans."

The students are asked how TCE could get into their homes. Remind class TCE is very
soluble in water.

Students consider how TCE can be removed from the drinking water supply.

Explain pink is good. TCE is a contaminant in the ground water in Tucson, Arizona. TCE
can be removed from the ground water by oxidation with potassium permanganate.
Potassium permanganate is pink. When it reacts with TCE, it is decolorized. “pink is
good” is a saying used by chemists who treat TCE in the water. If potassium
TCE Contamination and Cleanup Curriculum




permanganate is adding to the water and there is no more TCE, the water will be pink. If,
however, the potassium permanganate is decolorized, there may still be TCE in the
water.
This can be demonstrated by adding potassium permanganate solution drop wise into a
solution of acidified ferrous sulfate (a colorless solution representing contaminated
water). As the drops of purple potassium permanganate are added to the water, they
react with the TCE and are decolorized. But, as more potassium permanganate is added
the TCE is all treated and then when no more TCE is left, the solution is pink. It is now
safe because there is no TCE in the water.
Pose the question:
o How does this work? Explain this is a redox reaction; the potassium
permanganate (oxidizing agent) is reduced and the TCE is oxidized according to
the equation:
KMnO4 + C2Cl3H  CO2 + K+ + Cl- + H+ + MnO2

Students realize this equation is not balanced. Chemists need to balance the equation so
that they know how much potassium permanganate to add to the ground water. Too
much potassium permanganate can make you sick (though TCE is far worse).
When balancing a redox equation, refer to http://www.chemtutor.com/redox.htm. There
are three steps:
1. Assign oxidation states to the elements and ions
2. Balance the electron transfer. It is important that the same number of electrons
are used for the oxidation and reduction reactions
3. Without changing the electron transfer, balance the equation
Solution
KMnO4 + C2Cl3H  CO2 + K+ + Cl- + H+ + MnO2
+1 +7 -2
+1 -1 +1
+4 -2
+1
-1
+1
+4 -2
The Manganese and carbon atoms change oxidation state. All others remain unchanged. We
must balance the Manganese and Carbons. There are two carbons on the left side and 1 on
the right side. Therefore;
KMnO4 + C2Cl3H  2CO2 + K+ + Cl- + H+ + MnO2
The Manganese is reduced (gains 3 electrons) and the two Carbons are oxidized each (lose
3 electrons). Therefore, we have 6 electrons lost and 3 electrons gained. So, we need two
manganese;
2KMnO4 + C2Cl3H  2CO2 + K+ + Cl- + H+ + 2MnO2
The electron transfer can be added to the equation, but they should cancel each other out;
6e- + 2 KMnO4 + C2Cl3H  2 CO2 + K+ + Cl- + H+ + 2 MnO2 + 6e-
TCE Contamination and Cleanup Curriculum
Finally, the other elements/ ions should be balanced without affecting the electron transfer.
6e- + 2 KMnO4 + C2Cl3H  2 CO2 + 2K+ + 3Cl- + H+ + 2 MnO2 + 6eTo assess student knowledge, students can balance the redox reaction between PCE and
KMnO4. PCE (tetrachloroethylene) C2Cl4 is another contaminant found in ground water that can
be treated with potassium permanganate. Students should write a balanced equation for this
reaction. A redox lab is available at: http://www.sas.upenn.edu/~tloschia/AP/labs/iron-redox.htm.
Extension Using this equation, the students can calculate the mass of potassium
permanganate required to treat a million liters of water with 26 parts per billion of TCE. The
solution can be found on a power point presentation by Tucson students Kris Bjelk and Matt
Johnson.
Embedded Assessment
Successful balancing of the PCE oxidation with potassium permanganate will demonstrate
understanding of the concept. Further examples of redox reactions can be found at;
http://dbhs.wvusd.k12.ca.us/webdocs/Redox/Redox.html
Homework
n/a