Evaluation of a new laboratory exercise for
College Chemistry 1 at Madison College
Spring 2015
Sara Nason
Delta Program Intern, University of Wisconsin Madison
Advisor: Dr. Christen Smith
Chemistry Faculty, Madison College
Abstract
Many of the labs in College Chemistry 1 at Madison Area Technical College have limited
connection to things that students encounter outside of chemistry class. My project focused on
replacing a previous lab in the course with one that incorporates more realistic scientific investigation
and local environmental samples, and evaluating the impact of the new lab. The question I
investigated was: Will a lab with applied, real world applications increase student engagement and
understanding in College Chemistry I at Madison College? My hypothesis was that student
engagement will be higher in the lab with real world applications relative to labs with limited
connection to the students.
My evaluation methods for engagement in the lab were survey based. Over the course of the
semester, the students filled out a short survey each time they turned in a lab report. The survey had
four multiple choice questions that assess students' overall interest in the lab, what parts of the lab
were particularly interesting and helpful for their learning, and whether they understand how the
knowledge gained in the lab can be useful outside of chemistry class. Additionally, they wrote a onesentence summary of what they learned in the lab. At the end of the semester, students completed a
more comprehensive survey about the lab portion of the course and their future career plans. To
evaluate the academic effectiveness of the new lab, I assessed student lab reports for understanding
of the chemistry and environmental concepts that are key to the lab.
The survey results indicated that engagement in the new lab was similar to other labs in the course.
The new lab was especially popular among students in the medical field and who did not plan on
taking more chemistry. Students performed very well on the lab reports, and many wrote very
thoughtful question responses that linked the lab findings to the local environment. Overall, the new
lab was successful and should be considered for inclusion in future semesters of College Chemistry 1.
Research question: Will a lab with applied, real world applications increase student engagement and
understanding in College Chemistry I at Madison College?
Hypothesis: Student engagement will be higher in the lab with real world applications relative to labs
with limited connection to the students.
Introduction
Many of the labs in College Chemistry I at Madison College have limited connection to things
that students encounter outside of chemistry class. Most are focused on “identify the unknown” type
problems that are not representative of what scientists actually do. My Delta Program internship was
focused on replacing a previous lab in the course with one that incorporates more authentic scientific
investigation and local environmental samples, and evaluating the impact of the new lab. Specifically, I
wanted to test how the new lab impacted student engagement.
The definition of engagement has been conceptualized in many ways in recent literature. Some
authors take a simple approach, focusing on students psychological investment in learning,1 while others
define engagement as a multi-dimensional construct, typically with 2-3 components.2 For example, in
her 2010 book, Elizabeth Barkley defines engagement as the intersection of two components:
motivation and active learning,3 and Fredricks et al. separate the concept into three parts: behavioral,
emotional, and cognitive engagement.4 Behavioral engagement concerns behaviors such as effort and
participation, while emotional engagement includes having a positive attitude towards learning, an
interest in the material, and a sense of belonging and cognitive engagement is about investment in
learning.2,4 My project focused primarily on assessing emotional engagement in the College Chemistry I
lab setting.
Previously, professors at many institutions have introduced an environmental theme into their
chemistry classes as a way of making the material more accessible to students. This approach has been
used at multiple levels ranging from a one semester course for non-majors5 to upper level analytical
classes.6,7 Multiple college level chemistry curriculums with an environmental focus have been
published, including Chemistry in Context from the American Chemical Society8 and the Chem
Connections Project developed by the University of California at Berkley and Beloit College.9 In several
studies, it was found that chemistry classes focused on the environment may be better for student
attitude/engagement compared to traditional courses, but do not produce less gain in chemistry
knowledge.5,6,7 Environmentally based courses can also provide opportunities to introduce more
instrumentation and critical thinking into lab activities.
While redesigning the whole College Chemistry I course to focus on environmental applications
is outside the scope of a semester long Delta Internship, I wrote one new lab for the course (based on an
activity in the Chemistry in Context Laboratory Manual) that incorporates local environmental samples
and a standard analysis method (titration) that has not previously been introduced the course.8
Additionally, I taught the new lab as a guest instructor at Madison College and conducted student
surveys to evaluate the effectiveness of the new lab.
Approach Part 1: The Lab
My learning goals for students who performed the new lab were as follows:
1. Students will measure chloride in water samples by titrating with silver nitrate
a. Students will perform a titration using burettes
b. Students will use a colorimetric indicator solution
c. Students will use titration results to calculate chloride concentrations
2. Students will identify sources of chloride in local water bodies, wastewater, and drinking water
a. Students will relate their titration results to local sources of chloride
b. Students will compare and contrast the amount of chloride and sources of chloride for
different water sources
The lab is entitled “Measurement of Chloride in Local Water Samples” and is adapted from the
lab manual for Chemistry in Context, 4th ed..1 The water samples used in the lab included: local lake
water (Lake Mendota, Madison, WI), wastewater treatment effluent, and tap water from the lab sink. In
the pre-lab activity, students read about sources of chloride in the environment and made hypotheses
about which water samples would have the most and least amount of chloride. During the lab activity,
students worked together as a class to measure chloride levels in the three samples. Each pair of
students was assigned one water sample, which they analyzed in triplicate. Data from each lab section
was compiled for students to use in their final analysis. Students used the data from the titrations to
calculate the concentration of chloride in each sample and answered post lab questions that assessed
their understanding of both chloride sources in the environment and titrations. The full lab write up as
it was handed to students, is attached at the end as Appendix A. After the lab reports were turned in, I
reviewed them and assessed understanding using a rubric for each question.
Approach Part 2: Evaluation Methods
To evaluate student engagement with the new lab relative to other labs in the course, I used a
short survey, which the students filled out every time they turned in a lab report. The survey had five
questions: four multiple choice, and one open ended. The full text of the short survey is below:
1. I understand how the knowledge I gained in this lab may be used outside of chemistry class.
Strongly Agree
Agree
Neutral
Disagree
Strongly Disagree
2. This lab (as a whole) was interesting to me.
Strongly Agree
Agree
Neutral
Disagree
Strongly Disagree
3. These components of the lab were especially interesting to me (circle as many as apply):
a. Pre-Lab activity
d. Performing the data analysis
b. Pre-Lab discussion
e. Post-Lab questions
c. Performing the procedure
f. Other (please specify):
4. These components of the lab were especially helpful for my learning (circle as many as apply):
a. Pre-Lab assignment
e. Post-Lab questions
b. Pre-Lab discussion (in lab)
f. Other (please specify):
c. Performing the experiment
d. Data analysis
5. Write a one sentence summary of what you learned in this lab.
Students were assigned an alpha-numeric identifier at the beginning of the semester to avoid
association between their names and survey responses. Alpha-numeric identifiers were written at the
top of each survey.
In addition to the surveys about each lab report, a longer survey was given at the end of the
semester. This included 7 open ended and 4 multiple choice questions about students’ intended major,
planned future chemistry coursework, expected grade in the course, favorite lab exercise, memorable
parts of labs, recommendations for improving the lab portion of the course, and overall impressions of
the lab. The full text of the survey is included as Appendix B.
Results
Lab Report Responses
In general, student grades on the chloride lab were high, and answers to the pre and post lab
questions indicated good understanding of the material. A summary of student scores for each question
is shown in Table 1. 31/33 students wrote a well explained hypothesis about which water samples
would have the highest and lowest concentration and 31/33 were able to effectively write about
comparing their results with their hypothesis. Greater than 90% of students correctly used their
titration data to calculate the concentration of chloride in each sample. Additionally, Responses to postlab question four show that most students had a good understanding of how solubility rules were
important to the titration method; 76% of students were able to identify that NaNO3 would not be an
acceptable replacement for AgNO3 in the titration because the sodium ion will not react with the
chloride and chromate ions to form the precipitates necessary to determine the endpoint. An additional
15% of students demonstrated at least a partial understanding of this difficult question. Some quotes
from student lab reports are found in Appendix C. Common mistakes in the lab reports include not
averaging the data correctly and not using significant figures in the calculations.
Table 1: Lab Report Scores
Question
Pre-lab 1
Pre-lab 2
Pre-lab 3
Data Analysis
Post-lab 1
Post-lab 2
Post-lab 3
Post-lab 4
Points Possible
2
2
4
4
2
3
6
2
Average points
scored
1.94
1.88
3.91
3.64
1.94
2.7
5.7
1.68
Students receiving full
credit (n=33)
31
30
31
29
31
27
28
25
Weekly Survey Results
Student responses to the first two questions are summarized in Figure 1. We assigned a number
to each level of the Likert scale (from one for strongly disagree to five for strongly agree), and averaged
the results from all surveys for each lab. As the graph demonstrates, there was only small variations in
student responses across all of the labs, with the majority of students responding “Agree” (4) for each
question on all of the surveys.
Figure 1: Student responses to the first two questions on the short surveys given after each lab report
was turned in. There were minimal differences in responses between labs.
According to question three on the short survey, students found performing the experiment to
be the most interesting component of seven out of the nine labs assessed. Data analysis was the most
interesting component for the remaining labs, including the new lab on chloride measurement. The
responses to question four show that data analysis and post lab questions were the components most
helpful for learning in all but one lab. Students found that performing the experiments was the most
helpful component for the Mystery Solutions exercise. Table 2 shows the number of students that
circled each answer in questions three and four for each lab. Responses to questions three and four on
the survey regarding the chloride lab are shown in Figure 2.
There were a variety of student responses for question 5 on the chloride measurement lab
survey. Responses could be sorted into nine categories. Table 3 shows a summary of student
responses. In general, the responses to question 5 (write a one sentence summary of what you learned
in this lab) were fun to read, but provided little insight into student engagement with the labs. Thus, a
full qualitative analysis of student responses is not provided in this report.
Table 2: The number of students who listed each response for questions 3 (interesting components, blue)
and 4 (components helpful for learning, orange) on the weekly lab report surveys. The highest responses
for each lab are shown in bold, with darker fill color.
Lab Title
Pre-Lab
Assignment
Pre-Lab Discussion
Interest Learning Interest Learning
Performing the
Experiment
Interest
Data Analysis
Post-Lab
questions
Learning Interest Learning Interest Learning
Measurement
6
9
4
11
21
13
18
22
14
22
Chloride Measurement
4
8
11
11
17
15
21
21
17
19
Double Displacement
5
5
2
5
19
13
15
20
12
15
Activity of Metals
5
6
4
4
17
10
15
18
13
14
CuSO4 Spectroscopy
3
4
5
8
15
12
9
14
11
13
Hydrate Formula
7
13
7
10
10
9
14
14
6
15
Heat of Reaction
4
7
7
10
19
15
15
18
17
19
Mystery Solutions
4
4
8
8
18
19
14
14
12
14
Spectroscopy of Wine
4
5
6
10
20
14
14
20
11
13
Figure 2: Results for questions 3 and 4 on the short survey about the new lab – Analysis of Chloride in
Local Water Samples.
Table 3: Responses to question 5 regarding the new chloride lab
Number of
Responses
5
2
Category
-
-
Wastewater treatment does not remove Cl or there is a lot of Cl in effluent water
General comment about bad water quality
-
4
General comment on Cl is harmful and/or important to monitor
6
3
The amount of Cl in water varies or varied among our samples
I learned how to perform a titration
3
3
I learned how Cl reacts with AgNO3
I learned about real world applications of chemistry
2
4
General comment on measuring Cl
Off topic statement
-
-
-
Final Survey Results
All students expected to earn at least a B in College Chemistry 1, and feedback on the course
and instructor was very positive. Commonly mentioned “memorable experiences” include using the
spectrophotometer (5 students mentioned specifically) and learning to use Excel (3 students mentioned
specifically). 17 students wrote that nothing in the course needed to be changed and there were many
positive comments such as “It’s a great class”, “Christen is doing everything so well there is nothing I can
add”, and “Everything was very interesting/practical and related to lecture”. Criticisms included
uncomfortable chairs in the lab, a bad projector, and the need for more emphasis on calculations and sig
figs in class.
The majority of the 32 students who filled out the final survey fit in to one of two career groups.
18 students have plans to go into the medical field (self-reported majors include nursing, physician’s
assistant, biomedical engineering, medical school, medicine, pharmacy school, and radiation therapy)
while 13 plan to enter science and engineering fields (self-reported majors include biochemistry, food
science, biology, mechanical engineering, industrial engineering, and undecided engineering). One
student plans to go into business. The students can also be broken into groups based on whether or not
they plan to take additional chemistry classes, with 11 students planning to stop after College Chemistry
1 and 21 planning to continue at least through College Chemistry 2. These groupings serve as a useful
way to further break down the other data to compare between groups of students.
The responses to the Likert scale (1 indicates not at all, 10 indicates very much so) questions on
the final survey were largely positive, with average ratings of 8.3/10 for “Lab helped me understand
chemistry concepts”, 8.0/10 for “In lab, I learned how chemistry can be used in the real world” and
7.7/10 for “Lab was interesting and fun”. The average rating for “My experience in lab this semester was
different than my expectations for the course” was 5.6/10. Average rankings were higher for the
students planning to take more chemistry classes and for students planning to go into
science/engineering fields
26 students listed their favorite lab, with some listing more than one (all listed were included in
the analysis). The most popular lab overall was the Mystery Solutions exercise, with 8 students
identifying it as their favorite. Spectroscopy of Wine and Double Displacement Reactions were also
popular, with 5 responses each. Measurement of Chloride was identified as a favorite lab by 4 students.
Analysis of subsets of students is difficult due to the small number of responses and large number of
choices; the majority of labs appear to be equally popular across groups. However, all 4 students who
listed Measurement of Chloride as a favorite lab are in the medical field, and 3 do not plan to take more
chemistry classes.
The groupings of student can also be used to break down the weekly survey data. Figures 3 a
and b show student responses to the first two weekly survey questions separated by career path and
future plans. While responses showed only small variations, some trends can be deduced. For 8/9 labs,
the science and engineering students understood more about how the lab applied to the world outside
of chemistry class, while the medical career students found 7/9 labs more interesting. Students who
plan to take more chemistry classes found all of the labs more interesting and understood more outside
applications than students who do not plan to take more chemistry.
Figure 3 Weekly survey results separated by student career/major plans (a) and future chemistry course
plans (b)
Discussion
Lab Write-up
Student scores on lab reports indicate that most students achieved the proposed learning goals.
They were able to accurately report the class data and relate it to the hypotheses they made in the prelab. Additionally, they were able to answer questions about the chemistry behind the titration that
required higher order thinking (post-lab 3-4). While high grades are not necessarily an indicator of
student engagement, the complex and thoughtful responses given by some of the students (such as
those in Appendix C) indicate they put a lot of effort into thinking about the relationship between the
local geography and the lab results.
While students did well on the lab in its current form, there are several necessary improvements
that became obvious when reading the lab reports. When the lab is used in future semesters, the prelab reading should be edited to include more emphasis on water softeners and the fact that wastewater
treatment does NOT remove chloride. Several students wrote the opposite in their hypotheses. In the
procedure, more information should be given about specific details that students should write down in
their lab notebooks – for example, which water sample they were assigned and a description of the
color of the water sample before and after the titration. The data analysis and post lab sections should
be combined, and there should be a clear outline given for how the data should be averaged. Students
should be reminded to use sig figs and to show their work, even if the calculations are done in a
spreadsheet. While these additional details may not be necessary to include in a lab for a more
advanced class, College Chemistry 1 students tend to have little lab experience in a similar setting, and
this lab exercise took place near the beginning of the semester. The more detailed instructions should
lead to lab reports that are more structured so it is easier to assess student knowledge.
Survey Responses
The weekly lab surveys were intended to provide a basis for comparing the different lab
exercises. However, the results were very similar between labs and do not provide much insight into
how student engagement varied between labs. When the weekly survey results are separated based on
the self-reported information from the final survey, average responses are still all within 1.5 units on the
Likert scale. The lab that stands out the most in these comparisons is the Spectroscopy of Copper
Sulfate, which has the largest response gap between the students who plan to take more chemistry and
those who don’t and between the students pursuing a degree in the medical field and those pursuing
science/engineering degrees. Future improvements to the College Chemistry 1 curriculum may include
finding a way to make this lab more engaging for students who are pursuing medical careers and
students who do not plan to take more chemistry. However, the Copper Sulfate lab also received a lot
of positive feedback on the final surveys, as five students listed using the spectrophotometer (used in
both the Copper Sulfate lab and the Wine lab) as a memorable experience.
The weekly survey specifically about the Chloride Measurement lab shows that students found
the data analysis was the most interesting component of the lab and the component that most helped
their learning. This result makes sense, as the data analysis both required the use of molarity
calculations that were a concurrent topic in the lecture class, and revealed the results of the experiment.
For most of the other labs, performing the procedure was identified as the most interesting component,
but titrations (while an important staple of many general chemistry lab courses) are not very exciting to
perform, and due to the use of combined class data for analysis, students could not see any
environmentally relevant results while completing the procedure. Relative to the other labs, the
Chloride Measurement pre-lab discussion was identified as more interesting. This could indicate
increased engagement in this lab itself, or could be because there was a guest instructor teaching the
lab. The majority of the one sentence summaries of what was learned in the lab focused on
environmental applications such as water quality. This indicates that many students cared about the
implications of what was learned in the lab, beyond how to complete a titration. However, the lab
report scores show that the students adequately learned the chemistry concepts as well.
The chloride lab was listed as a favorite lab by four students on the final survey. None of the
four were science/engineering majors, and only one plans to take future chemistry classes. While this is
a small sample size, the Chloride Measurement lab appears to be especially popular amongst the groups
of students who generally have less interest in chemistry (according to the final survey). The Mystery
Solutions lab, listed most frequently as a favorite, is unique in that students develop their own
procedure for the lab. While it would be difficult to have students developing methods early in the
semester, future course updates could include redesigning some of the other labs to have more student
involvement in deciding on procedure details.
While it is difficult to make comparisons between labs using the data collected, the new lab on
Chloride Measurement seems to adequately engage students in learning about both environmental and
chemistry concepts. In that regard, it should be a considered a success and should be taken under
consideration for use in future semesters of College Chemistry 1.
Integration of the Delta Pillars
While teaching-as-research is the most obvious of the delta pillars featured in this project, there
were also components that encouraged building a learning community and learning through diversity.
One of the reasons I selected the chloride titration as the activity for the new lab, is that it has a
lot of relevance to the local water supply in Madison, WI. Two of the defining features of the city are its
beautiful lakes and cold winters. The cold winters mean that large amounts of salt are necessary to
keep the roads free of ice. However, too much salt use near the lakes could result in unsafe levels of
chloride in runoff water – which usually flows directly from storm drains into the lakes. Additionally, the
drinking water supply in Madison, which comes from groundwater, is very hard. To protect their pipes,
many households use water softeners, which discharge large amounts of chloride into the wastewater
treatment system, which in turn, discharges the chloride into water bodies outside of the city. Madison
is not very big, so there are many farms nearby, which was a good lead in for talking about agricultural
sources of chloride. By introducing the lab as having importance for the local environment, I was able to
focus on Madison College as part of a larger community and the importance of learning about chemistry
within that community.
While all of the students in the class go to school at Madison College, not all of them are from
Madison. During the pre-lab discussion, I asked the class about what they know about water quality,
and many of the students brought in knowledge from their experience outside of class. For example,
one student talked about being from “the country” and how different the drinking water is in Madison
than where she was from. Others mentioned run off from animal agriculture and that they had seen
algae and bacteria warnings for the local lakes. In the discussion, we were able to focus on relating the
diverse student experiences back to the lab activity of the day.
Additionally, each section working together as a Learning Community was essential for analyzing
enough samples to complete the lab. Analyzing a variety of samples was necessary to be able to
compare and contrast chloride levels in water from different sources. However, in the allotted time,
each group could only complete replicates for one sample. With 8 groups (2 students per group), each
section was able to get through all the samples with multiple replications for each one, leading to higher
quality data, which everyone was able to use for their lab reports.
As described above, the final survey results allowed me to break down the rest of the data by
intended major and by future chemistry plans. While the sample size was small, there were not large
differences between groups for most labs. The Copper Sulfate lab was identified as the exercise with
the largest engagement gap between groups. If I were to have a similar course evaluation in the future,
I would ask students to identify their gender and minority status. Breaking down the data using those
grouping may also be of interest.
References
(1)
Newmann, F. M.; Wehlage, G. G.; Lamborn, S. D. The Significance and Sources of Student
Engagement. In Student Engagement and Achievement in American Secondary Schools; Newman,
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(2)
Appleton, J. J.; Christenson, S. L.; Furlong, M. J. Student engagement with school: Critical
conceptual and methodological issues of the construct. Psychol. Sch. 2008, 45, 369–386.
(3)
Barkley, E. Student Engagement Techniques: A Handbook for College Faculty; John Wiley & Sons,
Inc.: San Fransisco, CA, 2010.
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Fredricks, J. A.; Blumenfeld, P. C.; Paris, A. H. School engagement: Potential of the concept, state
of the evidence. Rev. Educ. Res. 2004, 74, 59–109.
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Robelia, B.; McNeill, K.; Wammer, K.; Lawrenz, F. Investigating the Impact of Adding an
Environmental Focus to a Developmental Chemistry Course. J. Chem. Educ. 2010, 87, 216–220.
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Weidenhamer, J. D. Environmental Projects in the Quantitative Analysis Lab. J. Chem. Educ. 1997,
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Laboratory Manual - Chemistry in Context: Applying Chemistry to Society; Stratton, W. J.;
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Chem Connections Workbooks http://chemlinks.beloit.edu/ (accessed Sep 1, 2014).
Appendix A: Write up for new lab, as was handed to students
PRE-LAB FOR WEEK 4: Measurement of Chloride in Local Water Samples
This week, we will measure the concentration of chloride in various local water samples. The
chloride content of natural water samples depends, in part, on the geology of the area. However,
increased levels of chloride can indicate anthropogenic (human caused) sources. Dividing the
class to analyze different samples, we will measure chloride concentration of three water
samples:
1. Tap water from MATC campus: all tap water in Madison comes from wells
(groundwater).
2. Effluent water from the Nine Springs Wastewater Treatment Plant, which treats all of the
wastewater in the Madison metropolitan area. This water has been disinfected and is safe
for use in our lab.
3. Lake Mendota water – collected on 12/24/14 from the Terrace at UW-Madison
Note that chloride, Cl- is not the same as chlorine, Cl2. Chloride is an ion which is present in
common salts such as NaCl (table salt) and KCl (used as fertilizer, road salt, water softener salt).
Chlorine is a diatomic gas which is added to drinking water in small amounts, and to swimming
pools in somewhat larger amounts, as a disinfectant. However, chlorine is not a major source of
chloride.
In preparation for this activity, please read the following excerpts adapted from a 2012 report
from the Illinois State Water Survey 1 and answer the following Pre-lab questions before lab.
-----------------------------Introduction
Chloride (Cl-) is a naturally occurring major anion found in all natural waters. Chloride behaves
as a conservative ion in most aqueous environments, meaning its movement is not affected by
the interaction of water with soils, sediments, and rocks. As such, it can be used as an indicator
of other types of contamination. Unusually high concentrations can act as an “advance warning”
of the presence of other more toxic contaminants. Concentrations of Cl- in natural waters can
range from less than 1 milligram per liter (mg/L) in rainfall and some freshwater aquifers to
greater than 100,000 mg/L for very old groundwaters. Chloride is the most abundant ion in
seawater, with a concentration greater than 19,000 mg/L. Extremely elevated levels of Cl- in
surface water are generally due to significant evaporation (e.g., the Dead Sea has a Clconcentration > 230,000 mg/L).
Chloride is non-toxic to humans, but elevated levels make water unpotable due to the salty taste.
In the U.S., there is a secondary (non-enforced) drinking water standard of 250 mg/L, but in
areas of the world with water scarcities, drinking water can have considerably greater
concentrations of Cl-. Chloride is corrosive to steel, thus it may corrode pipes in water treatment
and industrial plants. Because it imparts a salty taste to water and is corrosive, elevated Cl- levels
in drinking water supplies can lead to increased treatment costs. Elevated Cl- in surface water has
been linked to damage of terrestrial and aquatic plants and aquatic animals at concentrations as
low as 210 mg/L. Increased Cl- concentrations in some environments have killed off native
vegetation and allowed invasive salt-tolerant species to thrive.
Anthropogenic Sources of Chloride in the environment
It is estimated that more than 140 teragrams (140 trillion kilograms) of Cl- are annually cycled
through various reservoirs on Earth, almost all of it due to human activities. Anthropogenic
sources include human sewage, livestock waste, water conditioning salt, synthetic fertilizer
(primarily KCl), brine disposal pits associated with oil fields, chemical and other industries, and,
in snowy climes, road salt runoff. From a volume standpoint, the most important anthropogenic
sources of Cl- to waters are fertilizer, road salt, water conditioning salt, sewage, and livestock
waste. Once in groundwater, Cl- and other contaminants can persist for many years if travel
times are slow. For example, Howard et al. (1993) estimated that if road salting was stopped
immediately in the Toronto area, it would be decades before the Cl- concentrations returned to
pre-1960 levels in shallow groundwater. In rural areas, agricultural sources of Cl- are of greater
importance.
Sources of Chloride from Urban Areas
Road salt has been linked to groundwater degradation in many urban and roadside areas in
snowy climes. Chloride concentrations have been increasing in surface waters and groundwater
in urban regions of the northern United States and Canada since the 1960s, primarily due to road
salt runoff. Two road salt runoff samples collected in Illinois had very high concentrations of Cl-:
1572 and 8930 mg/L, respectively.
In-home water treatment, specifically water softening, typically uses NaCl to recharge ion
exchange columns in order to reduce hardness (Ca2+ Mg2+) by replacement with Na+. For a
family of three or four with moderately hard water, the recommended amount of NaCl for water
softening is between 1.8 and 2.7 kilograms per day, or 600 to nearly 1000 kg of NaCl per year.
If the household is connected to a community waste treatment facility, the Cl- goes through the
wastewater treatment process, where it is not removed. Treated wastewater is generally
discharged directly into surface waterways and can have Cl- concentrations of up to 300 mg/L.
Sources of Chloride from Rural Areas
Animal waste contains very high concentrations of Cl- (up to 2000 mg/L). Because of this, even
relatively small concentrations of livestock can create a local problem for shallow groundwater.
Large confined animal feeding operations, which can concentrate thousands of animals in a
relatively small area, have the potential to produce more widespread contamination of shallow
groundwater, streams, and rivers.
KCl (potassium chloride) is the most commonly available potassium (K) fertilizer and usually
the cheapest, thus it is widely applied. Because it is spread over large areas, its impact on soil
water and groundwater quality is less than more concentrated Cl- applications, such as road salt,
but can still be significant.
Pre-Lab Questions
1. List two reasons why it is important to monitor chloride concentrations in the
environment:
2. Which anthropogenic (human caused) sources of chloride would you expect to be
important in an urban area, like Madison, WI? Which anthropogenic sources would you
expect to be important in rural areas of Wisconsin?
3. Which water sample in our experiment do you expect to have the highest concentration of
chloride? Which do you expect to have the lowest? Why (consider possible sources)?
The full report is available online at
http://www.isws.illinois.edu/pubdoc/B/ISWSB-74.pdf
(1)
Kelly, W. R.; Panno, S. V; Hackley, K. The Sources , Distribution , and Trends of
Chloride in the Waters of Illinois; Champaign, Illinois, 2012.
WEEK 4: Measurement of Chloride in Local Water Samples
OBJECTIVE
To measure the concentration of chloride in water samples taken from water sources in Madison,
WI using a titration with silver nitrate.
INTRODUCTION
Solutions containing chloride ions (Cl-) will react with silver nitrate (AgNO3) to form a
precipitate – AgCl, an insoluble white compound. (Other ions that are present in the water do not
participate in this reaction).
AgNO3 (aq) + Cl-(aq)  AgCl(s) + NO3-(aq)
(Equation 1)
This reaction is the basis for the titration method of analysis for chloride ions. In a titration, a
known volume of a water sample containing chloride ions is measured out, and then a solution of
AgNO3 is added slowly until just enough has been added to react with all of the chloride in the
sample. If the volume of AgNO3 added and its concentration are known, it is possible to
calculate how much chloride must have been present to react with all the AgNO3.
To assess the endpoint of the titration (when enough AgNO3 has been added), a small amount of
an indicator solution is added to the water sample. We will use sodium chromate (Na2CrO4) as
our indicator. Chromate ions are yellow, but they react with silver ions to for a red precipitate
(Ag2CrO4).
2Ag+(aq) + CrO42-(aq)  Ag2CrO4(s)
(Equation 2)
Over the course of the titration, as AgNO3 is added to the water sample, the chloride is
precipitated as white AgCl. After all the chloride has been removed, the silver ions will react
with CrO42- to form red Ag2CrO4. The appearance of this red precipitate signals the end of the
titration. It is important to stop adding AgNO3 exactly when you start to see the red precipitate
to ensure accuracy.
To measure the amount of AgNO3 added and to control its flow into the water sample, you will
use a burette: a glass tube with volume markings and a valve on the end (see picture below).
This method is commonly used for titrations and allows for good accuracy when used correctly.
We will be using molarity (M) as our unit of concentration in this experiment. A 1.0 M solution
contains 1.0 mole of solute per liter of solution. The metric prefixes can be used with this unit
(ex. 1 M = 1000 mM).
PROCEDURE
Materials
Equipment
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Burette, with ring stand and clamp
Magnetic stir plate and stir bar
250 mL Erlenmeyer flask
Gloves
Goggles
Apron (optional - to protect clothing from stains)
Chemicals
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Water samples (see below)
0.25 M Na2CrO4
0.010 M AgNO3
***Safety Notes: Sodium chromate is considered to be a carcinogen. Silver Nitrate will stain
your skin, so be careful not to get it on your hands. The stain is ugly, but harmless and will wear
off in a few days***
Water Samples
1. Tap water from MATC campus: all tap water in Madison come from groundwater
2. Effluent water from the Nine Springs Wastewater Treatment Plant, which treats all of
the wastewater in the Madison metropolitan area. This water has been disinfected
and is safe for use in our lab.
3. Lake Mendota water – collected on 12/24/14 from the Terrace at UW-Madison
Each group will be assigned ONE water sample to test. You will analyze data from the entire
class for the post-lab analysis.
1. If you are assigned the tap water or Lake Mendota water sample, use a 250 mL graduated
cylinder to measure 100.0 mL of your assigned water sample. If you are assigned the
effluent water sample, use a 100 mL graduated cylinder to measure 25.0 mL of the
sample. Transfer your sample to a 250 mL Erlenmeyer flask.
2. Add 2 drops of indicator solution (0.25 M Na2CrO4) to the flask and observe the color of
the solution.
3. Put the flask on a magnetic stir plate and add a clean stir bar. Slowly turn the stir plate on
so that solution is gently mixing.
4. Obtain a clean dry burette.
5. Fill the burette to the 0 mark with 0.010 M AgNO3 and position the flask and stir plate
under the burette.
6. Slowly add AgNO3 to the flask little by little until a red precipitate forms and does not go
away as the solution mixes. The mixture should appear light orange/pink in color when
you stop adding AgNO3**. Record the volume of AgNO3 added. If you empty the
burette and have not yet seen a color change, you may need to refill the burette with
0.010 M AgNO3. Make sure you record the total volume of AgNO3 added in your lab
notebook.
**Note: If the solution turns bright red, you have added too much AgNO3, and will need to
start over. There will be an example solution at the front of the room that shows the correct
color for the end point.
7. Refill the burette to the 0 mark with AgNO3 and repeat the titration of the same assigned
water sample (using a clean flask).
8. When you finish the second titration, check with your instructor to determine whether
you need to repeat the titration a third time.
9. Calculate the average volume of AgNO3 added (in milliliters) for your repeated titrations.
Record the average value on the group spreadsheet on the computer at the front of the
room. Also record the volume of your initial water sample (100.0 mL or 25.0 mL).
DATA ANALYSIS
The chemical equation for the reaction of chloride with silver nitrate shows that one mole of
AgNO3 is needed to react with one mole of Cl-.
AgNO3 (aq) + Cl-(aq)  AgCl(s) + NO3-(aq)
(Equation 1)
Thus, at the end point of the titration, the number of moles of silver nitrate added is exactly equal
to the number of moles of chloride present in the water sample. Mathematically, we can say
that:
The number of moles of AgNO3 added can be calculated from the volume and the molarity
(moles per liter) of the solution added:
A similar equation can be written for moles of chloride in the water sample:
Substituting into the first equation, we can write:
Which can be rearranged to the form:
This is the equation you should use for your analysis.
For your data analysis, use the spreadsheet with data from the whole lab section. The
spreadsheet will be posted on the course website the day after lab.
Begin by calculating the average volume of AgNO3 added for each of the three samples. Then
use the above equation to calculate the molarity of chloride in each sample (remember to use the
correct units).
POST-LAB QUESTIONS
1. Which water sample that the class tested has the highest concentration of chloride?
Which has the lowest? Write 1-2 sentences comparing your results to the predictions you
made in the pre-lab questions.
2. Convert the concentration of chloride for each sample the class tested from units of
molarity (moles per liter) to mg/L (1 mole chloride = 35.45 g). Chloride has negative
impacts on aquatic wildlife at 210 mg/L. Write 1-2 sentences explaining whether or not
the chloride concentrations in the tested water samples are cause for concern.
3. For the class next semester, Sara is planning to collect additional water samples from
three streams: one in a pristine mountain area with no cities or farms nearby, one
surrounded by corn fields near a large dairy farm, and one in an urban area where snow
melt from the roads and treated wastewater are discharged into the stream. Answer the
following questions about what you would expect to find in these samples:
a. Which sample is likely to have most chloride? Least chloride? Why (consider
possible sources)?
b. Based on your answer to part a, which sample will require the most AgNO3 to
titrate a 100 mL sample? Why? Write 1-3 complete sentences.
4. If you used NaNO3 instead of AgNO3 would the titration still work? Why or why not?
(hint: consider what changes in Equation 1) Write 1-2 complete sentences to explain your
answer.
Appendix B: Final Survey
Alpha-Numeric ID: _____________________________
(first two letters of your street name followed by the last two digits in your phone number)
1. What is your intended major, degree program, or academic plan?
2. What grade do you expect to earn in College Chemistry 1 this semester?
3. What chemistry classes had you taken prior to College Chemistry 1?
4. Describe your lab experience from before College Chemistry 1.
5. Do you plan on taking any chemistry classes in the future? If so, which ones?
6. What was your most memorable experience in College Chemistry 1 Lab? What was your
favorite experiment? What lab skills did you learn?
7. What would you recommend changing in future semesters of College Chemistry 1?
Rate the following statements about lab for College Chemistry 1 on a scale of 1 to 10:
1. Lab helped me understand chemistry concepts
1-------2-------3------4-------5-------6-------7-------8-------9-------10
(not at all)
(very much so)
2. In lab, I learned how chemistry can be used in the real world
1-------2-------3------4-------5-------6-------7-------8-------9-------10
(not at all)
(very much so)
3. My experience in lab this semester was different than my expectations for the course
1-------2-------3------4-------5-------6-------7-------8-------9-------10
(not at all)
(It was exactly what I expected)
(very much so)
(It was different from what I expected)
4. Lab was interesting and fun.
1-------2-------3------4-------5-------6-------7-------8-------9-------10
(not at all)
Comments:
(very much so)
Appendix C: Insightful responses to lab report questions from various
students
Pre-lab question #1
“It is important to monitor chloride concentrations in the environment for a few reasons. One reason is
that animal waste has a high concentration of Cl- and has the potential to contaminate shallow streams,
ground water, and rivers….”
Pre-lab question #2
“I would expect that one of the most significant anthropogenic sources of Cl- in the Madison area is road
salt”
Pre-lab question #3
“I expect Lake Mendota to have the highest concentration of Cl- because of all of the road salt use this
winter. I expect the MATC to have the lowest concentration because there is (not) that much road salt
and fertilizer soaking into the groundwater compared to everywhere else in Madison.”
“I think that these three water sources will be fairly similar in Cl- levels. The wastewater treatment plant
does not remove Cl- ions, so it will contain a significant concentration from residential hard-water
treatment and road salt that has washed into sewers. Lake Mendota likely has a large amount of road
salt run off and there are also farms near the lake on the NW side, between Middleton and Waunaukee,
which could introduce a source of Cl- from fertilizer.”
Post-lab question #4
“The result of mixing NaNO3 with Cl- would result in sodium chloride and nitrate, both of which are
soluble in water. With the absence of silver in the solution, there would be no reaction with the
indicator that the titration is complete.”
“If NaNO3 were used instead of AgNO3, the reaction would look very different:
NaNO3 (aq) + Cl-(aq)  NaCl(aq) + NO3-(aq)
Notice that in this case, all reactants and products are aqueous. The total ionic equation would then be:
Na+ + NO3- + Cl-  Na+ + Cl-+ NO3Hence the net ionic equation would be (no reaction). Since no precipitate would form, there would be
no means of measuring the concentration of Cl- ions in solution.”