Using Student-Developed, Inquiry-Based Experiments To Investigate

Research: Science and Education

Using Student-Developed, Inquiry-Based Experiments To Investigate the Contributions of Ca and Mg to Water Hardness Shui-Ping Yang* and Chung-Chia Li Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan; *[email protected]

Water is critical to our daily life. Most people drink about a quart of water each day. Water quality has become a very big issue today. Determining total water hardness is an important in water quality monitoring for environmental protection agencies in any country. It is also a popular experiment in general chemistry laboratories. Since calcium and magnesium ions are the main contributors to total water hardness, these raise an interesting problem about our drinking water: “How much do individual calcium and magnesium concentrations contribute to water hardness?” Solving this problem is very difficult because calcium and magnesium are “twin” metals with highly similar properties, and few previous studies related to this topic are available. These difficulties create a challenging opportunity for undergraduate chemistry students. In our activity, students were instructed to design their own experiments to solve this water-quality problem using inquiry-based learning. This learning approach emphasizes student-developed experiments. It is very different from traditional learning approaches that involve investigation by procedure-given instructions. The Context for This Project Total water hardness is typically determined by complexometric titration. This method appears in textbooks (1–2) and on the Internet (3–5). Chemical education literature reports that the titration is also used in seawater analysis and water projects (6, 7) and in quantitative analyses of some consumer products (8–10). In terms of individual calcium and magnesium determinations, the Internet offers few experiments associated with detailed procedures (11–12). Previous studies applied complexometry without describing procedures (13, 14). However, these determinations are invariably conducted by dependent calculations rather than by independent protocols. Dependent calculation values can be calculated by subtracting individual metallic concentrations (determined by independent protocol) from total water hardness. However, dependent calculations suffer from potential errors that derive from lower accuracy for total water hardness or for individual metallic concentration. On the other hand, independent protocols are chemically significant to confirmative evaluation. In our activity students designed their own independent protocols for individual calcium and magnesium concentration determinations. Student independent protocols were evaluated in multiple ways by comparing student results for individual metallic concentrations with expected standard values, with student results from total water hardness, and with instructor results by spectrophotometry. Determining individual metallic concentrations in water by complexometry involves four variables (experimental conditions): complexometric titrants, masking agents, metal ion indicators, and controlled pH values. These offer chemical and educational opportunities in student inquiry-based learning due to the extensive content knowledge. Nowadays, inquiry-based learning has become a common instruction method in the science disciplines. Some educators are convinced that inquiry-based activities greatly 506

enhance pedagogical value in the chemical laboratory (15). At least three inquiry-based general chemistry laboratory textbooks have been published since 2000 (16–17). Chemical education journals also have published several inquiry-based approaches for the general chemistry laboratory. These approaches include: Web-based inquiry study (19), graduate teaching assistant training and inquiry-based instruction (20), a guided-inquiry format for general chemistry laboratory (21), inquiry-based classroom activity (22), discovery learning (23), prompted inquiry-based learning (24), exploring zinc atomic layers in galvanized iron coating (25), and inquiry-based instruction effects (26). Moreover, designing an experiment is an important requirement for an inquiry-based approach to chemical investigation. Chemical education literature has presented student-designed experiments for a wide array of topics at the undergraduate level, covering general chemistry and physical chemistry (27–29), analytical chemistry (30–31), and organic chemistry (32–35). However, none of these inquiry-based approaches and these student-designed experiments emphasized the processes of literature search and discussion, and designing trial procedures. In addition, experimental accuracy and precision were not statistically evaluated by comparison. In our activity student-developed experiments were evaluated by statistic analysis. In most cases chemistry students learn problem-solving skills through virtual situations in the classroom rather than in the laboratory. However, real-world problem solving has recently been integrated into general chemistry experiments (6, 24–25). In our activity students mimic a scientific research process through inquiry-based learning to solve a real-world water-quality problem. Students are instructed to perform these three progressive processes: (i) literature search and discussion; (ii) designing, testing, and evaluating their own trial procedures; and (iii) developing, performing, and evaluating their own experiments. As mentioned above, the first two processes have scant representation in the literature. Pedagogical Benefits The benefits for students focus on inquiry-based and science process skills gained and the content knowledge and laboratory techniques learned in this activity. Inquiry-Based and Science Process Skills Inquiry-based learning and problem-solving skills developed with this lab include:

• Searching the scientific literature and leading discussions on their findings and the relevance for their experiment

• Working cooperatively in small groups and participating in team discussions

• Using a multivariable, problem-solving learning process to create and test their experiments

• Designing, testing, and evaluating their trial procedures

• Developing and performing their own experiments

Journal of Chemical Education • Vol. 86 No. 4 April 2009 • www.JCE.DivCHED.org • © Division of Chemical Education


Content Knowledge and Laboratory Techniques Chemistry content and laboratory techniques learned by students undertaking this activity include:

• Understanding complexometry and effectively using complexometric titrants, masking agents, metal ion indicators, and buffer solutions

• Practicing and mastering quantitative analysis relating to water quality, total water hardness, and determining individual calcium and magnesium concentrations

• Achieving proficiency in complexometric titration techniques, designing independent protocols, and making accurate dependent calculations

Methodology Instructional Strategies In previous general chemistry laboratory work, students undertook experiments to determine total water hardness by complexometry through traditional lab instruction. In this inquiry-based activity, students were expected to use complexometry associated with masking agents to develop their own independent protocols and then to determine individual calcium and magnesium concentrations in a volume of water. Students were encouraged to mimic scientific research work using three, three-hour laboratory sessions. Table 1 shows the process outline by activity or task for each week in the project. The student handout (in the online supplement) describes student and instructor tasks in greater detail. In this activity, 48 students (chemistry majors) were assigned to work either as individuals, in a group of two students, in a team of six students, or as the whole class depending on task characteristics, experimental limitations, and process stages. Student teams chose their partners. The students were predominantly 18 years old (79%), although some were 19 (17%), and a few were 20 years old (4%). The class was nearly balanced with 27 males (56%) and 21 females (44%). Most of the students were interested in chemistry. During Week I, students were first introduced to this activity process, given content background—especially for the crucial concept of “metallic mask effect” (i.e., triethanolamine can be used to mask aluminum ions for the magnesium determination), and provided with strategies for the literature search through a mini-lesson. Then individual students searched the previous literature and designed tentative procedures through homework assignments.

During Week II, the class was divided into eight teams (with six students per team) who jointly used a bench. First, each team discussed the results of the literature search to decide whether they had useful material or not. They shared useful findings from the literature with the class and discussed it with the instructor. Second, students were helped to classify useful literature into distinguishable independent protocols for individual metallic determinations according to the four variables (complexometric titrants, masking agents, metal ion indicators, and controlled pH values). Each team was then assigned two different independent protocols for individual calcium and magnesium determinations. The teams were further divided into three groups (with two students per group) to test their trial procedures. Finally, students calculated percent errors for their experimental results to evaluate the effectiveness of their designed procedures when analyzing standardized concentrations of individual samples of calcium and magnesium. During Week III, each team shared their findings about evaluating trial procedures with the class. Independent protocols evaluated as having a high or middle degree of feasibility were continually assigned to be templates for developing exact experiments; those evaluated as having low feasibility were abandoned. The groups within a team continued to perform their own experiments and make minor modifications. To evaluate the feasibility of their exact experiments, the different percentages between experimental data from independent protocols and the values from dependent calculations for a tap water sample from our laboratory were analyzed. Openness Levels of This Activity Investigating individual calcium and magnesium concentrations in water is a very difficult issue for first-year chemistry majors. We think that general chemistry students cannot successfully design independent protocols without completing a gradual preparation process. In 1962, Schwab described three levels of openness in laboratory instruction (36). In 1971, Herron elaborated this into four levels of laboratory openness (37). Levels 0–3 were suggested as criteria. Each level is determined by the openness of the questions, ways and means, and answers. A Level 3 activity is one in which the questions, ways and means, and answers are all open-ended. A Level 2 activity is one in which only questions are given, and the ways and means and answers open-ended. A Level 1 activity is one in which questions and ways and means are given with only the answers being open-ended. A Level 0 activity is one in which the questions, ways and means and answers are given. Based on the Schwab–Herron openness levels, this activity occurs at a range of 0–2 openness levels, and

Table 1. Distribution of Student Activities and Tasks by Sequence in the Process Sequence

Week I: Literature Search and Designing Tentative Experiments

Week II: Discussing Literature and Designing and Testing Trial Procedures

Week III: Sharing Findings and Performing Exact Experiments

1

Introduction to activity process

Dividing the class into teams

Sharing findings with class

2

Introduction to content background

Team discussion on literature

Assigning group tasks

3

Tips for literature search

Sharing literature with class

Performing exact experiments

4

Searching the literature

Assigning team tasks

Sharing results of exact experiments

5

Designing tentative procedures

Designing trial procedures

6

Testing trial procedures

© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 4 April 2009 • Journal of Chemical Education

507


Evaluating Student-Developed Experiments

slowly decreases with time. Table 2 presents the variation of the question, procedure, answer, and openness levels at the end of the stages of this activity. Five out of nine stages listed in Table 2 rated either “2”, “Near 2”, or “Between 1 and 2” in openness levels. The designation “Between 1 and 2” acknowledges that procedural openness depends on students’ previous experiences. This example of inquiry-based learning emphasizes gradual progress to facilitate student independent-protocol development.

Students’ experimental data from designing their trial procedures and experiments were evaluated by quantitative analysis. Student feedback on learning impacts was summarized into categories and evaluated by qualitative analysis. The instructor discussed the results of the literature searches with the students and together determined which articles from the literature would be useful for designing their trial procedures. Student-submitted experimental conditions were classified into distinguishable independent protocols according to the four variables. Students used percentage errors to evaluate the feasibility of their designing trial procedures at that time. The instructor used quantitative analysis—the two-tailed t test and the one-sided F test, respectively—to evaluate experimental accuracy and precision differences for student-designed trial procedures after completing this activity (see Table 3). Moreover, the instructor used the the two-tailed t test and the one-sided F test to evaluate the average and precise differences between student-developed experiments and dependent

Hazards Associated with the Experiments This activity involves actual laboratory work during Weeks II and III. Chemicals used in the experiments include EDTA, masking agents, metallic ion indicators, and buffer solutions. Sodium hydroxide is corrosive and may cause severe burns to exposed skin; ammonia may cause eye and skin burns. Hydrochloric acid may cause irreversible eye injury and its vapor or mist may cause irritation and severe burns. Ammonium oxalate is poisonous by ingestion and inhalation and should be avoided. The online supplement provides more detailed safety information.

Table 2. Openness Levels of the Stages of the Activity Problem

Procedure

Answer

Openness Levela

Mini-lesson (how to search the literature)

Given

Open

Open

2

Week I

Searching literature

Given

Known/Openb

Open

Near 2

Week I

Designing tentative procedures

Given

Known/Openb

Open

Near 2

Given

Known/Openb

Open

Between 1 and 2

Open

Between 1 and 2

Week

Stage

Week I

Week II

Discussing literature

Week II

Designing trial procedures

Given

Known/Openb

Week II

Testing trial procedures

Given

Known

Open

1

Week III

Sharing results of trial procedures

Given

Known

Open

1

Week III

Performing exact experiments

Given

Known

Known

0

Week III

Sharing results of exact experiments

Given

Known

Known

0

aSee

37 bDuring

refs 36 and literature search and trial design procedures, students sometimes knew how to design a procedure and sometimes did not, depending on their comprehension (e.g., the openness level of discussing literature [near 1] is smaller than that for searching literature [near 2]).

Table 3. Comparison of Results from Student-Designed Trial Procedures with Standard Values Method

Trial Means/ mmol

Standard Means/ mmol

Mean Difference/ mmol

Percent Error, %

Rated Feasibility (Low–High)

SD Differencea/ mmol

t Values

p Values,

Ca-A

0.1131

0.1000

0.0131

13.1

middle

0.0126

2.532

0.052

Ca-B

0.0656

0.0600

0.0056

9.4

high

0.0027

3.885

0.018b

0.35

0.830

0.37

0.848

Students’ Trials

F Values

1.0

× 108

p Values, Standard Procedures

0.000d

Ca-C

0.0831

0.0750

0.0081

10.8

middle

0.0026

5.411

0.003c

Ca-E

0.0669

0.0500

0.0169

33.8

low

0.0046

8.279

0.001d

—e

—e

Mg-A

0.1628

0.0500

0.1128

225.7

low

0.0004

564.720

0.000d

—e

—e

Mg-B

0.0813

0.0300

0.0513

170.9

low

0.0049

14.254

0.000d

1.01

0.495

Mg-C

0.0324

0.0250

0.0074

29.7

middle

0.0069

2.398

0.074

—e

—e

Mg-D

0.0245

0.0250

−0.0005

−2.1

high

0.0046

0.279

0.791

aDifference eThe

of standard deviation bThe value is significant at p < 0.05 variance of standard values is zero.

508

cThe

value is significant at p < 0.01

dThe

1.0

× 108

0.000d

value is significant at p < 0.001.



calculations and among different analytical methods (see Tables 4 and 5).

Results and Discussion Student Literature Searches and Discussions Following the mini-lesson on strategies for conducting a literature search in Week I, students searched the scientific literature for information to help them with designing their own experimental procedures. A bibliography in the online supplement provides a summary of several useful literature citations (including those on masking agents and metallic ion indicators). Based on the authors’ reviews, none of the students’ literature searches yielded useful material with step-by-step complexometric procedures delineated. Two relevant examples from the literature concerning masking agents are described below (13, 38).

• In the clear Ca2+ solution, place 2 mL of deionized water. Add diluted NH3 until the solution is alkaline by litmus paper detection. Add 2 drops of 0.3 M (NH4)2C2O4 to the mixture. Stir it for 1 min and let it stand for 2 min. If white CaC2O4 precipitates, Ca2+ is present.

We note that the two examples quoted above describe using hydroxide and oxalate to precipitate with magnesium and calcium, respectively, as masking agents. Student-Submitted Experimental Conditions Students were expected to develop at least two different independent protocols for individual calcium and magnesium determinations, respectively. As mentioned earlier, four variables (experimental conditions) were used as a framework, which were initially set by the instructor; students were given an example of the calcium determination. Through literature searches and sharing useful information in class discussions, students identified four variables to distinguish independent protocols. The four variables principally dominated the students’ independentprotocol development. Students found five methods (independent protocols) for individual calcium determination (the Ca-A method was provided by the instructor). These experimental conditions include two complexometric titrants (EDTA and EGTA), two masking agents (NaOH and a mixture of Na2HPO4 and NH4OH), five metallic ion indicators (calcon, hydroxynaphthol blue, murexide, NN, and EBT), and three controlled pH values (high pH, pH 12–13, and pH 10). Additional details are provided

• Calcium occurs frequently in the form of a carbonate (for example, limestone) and may be in the presence of a significant amount of magnesium. The usual EDTA titration at pH 10, with eriochrome black T as an indicator, does not differentiate between Ca and Mg. Using a hydroxynaphthol blue indicator, the analyst can titrate calcium in the presence of magnesium. At pH 12 or 13 magnesium forms Mg(OH)2, which prevents its interference, but the titration must be carried out quickly to avoid removing calcium by coprecipitation. Also, excess EDTA will start to complex magnesium so that a fading endpoint may occur.

Table 4. Comparison of Student-Developed Experiments with Dependent Calculations Tacticsa

Exact vs DCV

Exact Means, ppm

DCV Means, ppm

Mean Difference, ppm

Mean Difference, %

SD Difference,b ppm

t Values

p Values,

F Values

p Values, Standard Procedure

Ca-A vs total minus Mg

85.2

80.5

4.7

5.9

−5.7

3.63

0.036c

5.04

0.017c

Ca-B vs total minus Mg

82.8

80.5

2.3

2.9

−6.6

2.33

0.258z

3.54

0.085z

Ca-C vs total minus Mg

84.4

80.5

3.9

4.8

−5.5

2.59

0.081z

4.38

0.027c

Mg-C vs total minus Ca

41.4

37.5

3.9

10.3

3.6

1.92

0.103z

8.34

0.007d

Mg-D vs total minus Ca

41.6

37.5

4.1

10.8

7.5

1.08

0.331z

25.88

0.000e

aDifferent

deviation

Students’ Trials

tactics represent individual metallic determinations (exact values) versus dependent calculation values (DCV) bDifference of standard cThe value is significant at p < 0.05 dThe value is significant at p < 0.01 eThe value is significant at p < 0.001

Table 5. Comparison of Different Analytical Methods Exact Means, ppm

Spec Means, ppm

Mean Difference, ppm

Mean Difference, %

SD Difference,b ppm

t Values

p Values,

F Values

p Values, Standard Procedure

Ca-A vs Ca-Spec

85.2

83.5

1.8

2.1

−0.5

2.11

0.125

0.69

0.606z

Ca-B vs Ca-Spec

82.8

83.5

−0.6

−0.7

−1.4

1.00

0.500

1.33

0.313z

Ca-C vs Ca-Spec

84.4

83.5

1.0

1.1

−0.3

0.95

0.411

0.36

0.786z

Mg-C vs Mg-Spec

41.4

38.0

3.4

8.9

4.7

1.69

0.142

58.96

0.001c

Mg-D vs Mg-Spec

41.6

38.0

3.6

9.4

8.6

0.95

0.386

179.27

0.000c

Methodsa

Exact vs Spec

aDifferent cThe

methods represent individual metal determination versus UV–vis spectrophotometry (Spec) value is significant at p < 0.001.

Students’ Trials

bDifference

of standard deviation


509


in Table 6. Except for the Ca-F method, individual calcium concentration is determined by the magnesium exclusion from Mg(OH)2 and MgNH4PO4 precipitations. The Ca-F method operates on the principle that the EGTA–Ca complex is much greater in stability constant than the EGTA–Mg complex. The experimental conditions of each method are interdependent. Upon reviewing what chemicals would be needed we discovered that the EGTA titrant and the NN indicator were not available to us; thus, the Ca-D and Ca-F methods were not tested for their feasibility. These three chemical equations involve the masking effect and complexometric titration for the calcium determination. Mg2 (aq) 2OH (aq)

Mg(OH)2(s)

(1)

HPO42 (aq) Mg2 (aq)

NH4 (aq) OH(aq)

Ca2 (aq) H2EDTA2 (aq)

(2)

MgNH4PO4(s) H2O(l) CaEDTA2 (aq) 2H (aq)

(3)

For determining magnesium in water, students found six methods (Table 7). These experimental conditions contain a

complexing agent (EDTA), four masking agents (tartrate, sucrose, oxalate, and fluoride), two metallic ion indicators (EBT and PV) and three controlled pH values (high pH, pH 8–10, and pH 10). Except for the Mg-A and Mg-B methods, individual magnesium concentration was determined by calcium exclusion from CaC2O4 and CaF2 precipitations. The experimental conditions of each method are interdependent. The proposed Mg-E and Mg-F methods were not tested for their feasibility: fluoride ion was not available to us, and, following class discussion of the material safety data sheets for chloroform—which is highly toxic—it was decided not to use that chemical compound for these tests. Equations 4–6 are three chemical equations involved with masking agents and complexometric titration for magnesium determination. Tartrate and sucrose are ineffective as the calcium masking agent (see Table 3).

Ca2 (aq) C2O42 (aq)

Ca2 (aq) 2 F (aq)

Mg2 (aq) H2EDTA2 (aq)

CaC2O4(s)

(4)

CaF2(s)

(5)

MgEDTA2 (aq) + 2H (aq) (6)

Table 6. Experimental Conditions for Individual Calcium Determination Method

Complexometric Titrant

Masking Agent

Metal Ion Indicator

Color Change of Indicator

Ca-A

EDTA

Ca-B

Controlled pH Value

Note

hydroxide (OH−)

calcon

—

high pH

—

EDTA

hydroxide (OH−)

hydroxynaphthol blue

—

pH 12 or 13

Mg(OH)2 ppt

Ca-C

EDTA

hydroxide (OH−)

murexide

blue-violet–red

pH above 12

—

Ca-D

EDTA

hydroxide (OH−)

NN (not available)

blue–red

pH 12–13

Mg(OH)2 ppt

Ca-E

EDTA

Na2HPO4 + NH4OH

—

—

—

MgNH4PO4 ppt (personal idea)

Ca-F

EGTA (not available)

not needed

eriochrome black T

wine red– pure blue

pH 10; NH3/NH4Cl

Mg2+ does not interfere with EGTA

Method

Complexometric Titrant

Masking Agent

Metal Ion Indicator

Color Change of Indicator

Controlled pH Value

Note

Mg-A

EDTA

tartrate

—

—

high pH

—

Mg-B

EDTA

sucrose

—

—

high pH

—

Mg-C

EDTA

oxalate (C2O42−)

eriochrome black T


pH 8–10

personal ideas

Mg-D

EDTA

oxalate (C2O42−)

pyrocatechol violet

purple–blue

pH 10

—

Mg-E

EDTA

fluoride (F−) (not available)

eriochrome black T


pH 10; NH3/ NH4Cl

CaF2 ppt (personal idea)

Mg-F

EDTA

oxalate (C2O42−)

eriochrome black T


—

extraction with chloroform (high toxicity)

Table 7. Experimental Conditions for Individual Magnesium Determination

510



Student-Designed Trial Procedures After submitting experimental conditions, student teams were assigned two different methods to design their own trial procedures and then to determine individual calcium and magnesium concentrations using at least three trials for each determination. Student-designed trial procedures were evaluated by error percentage through testing a standardized solution of 1.000 mM calcium and 0.5000 mM magnesium (as standard values) using high purity chemicals prepared by a TA. This evaluation divided the feasibility of student-designed trial procedures into three levels based on error percentage—high (less than 10%), middle (10–30%), and low (more than 30%). The trial means in Table 3 compare the results from student-designed trial procedures (trial means) with standard values (standard means) and their feasibility. Here, error percentage values were analyzed by the students at that time and the t test and F test results were evaluated by the instructor. Results based on error percentage values indicated five methods (Ca-A, Ca-B, Ca-C, Mg-C, and Mg-D) had high or middle feasibility, and three methods (Ca-E, Mg-A, and Mg-B) had low feasibility. The two-tailed t test indicated that no differences existed in the average between the results from student-designed trial procedures and standard values for the Ca-A, Mg-C, and Mg-D methods. The Ca-B and Ca-C methods were significantly different in averages ( p < 0.05 and p < 0.01, respectively). The Ca-E, Mg-A, and Mg-B methods were significantly different in the average ( p < 0.001). The one-sided F test showed that no differences existed in the precision between results from student-designed trial procedures and standard values for the Ca-B, Ca-C, and Mg-B methods. The precision of the Ca-A and Mg-D methods was significantly worse ( p < 0.001). The five methods with high–middle feasibility served as templates (with minor modification) for student-developed exact experiments conducted the following week. Student-Developed Experiments To evaluate student-developed exact experiments in Week III, a tap water sample taken from our laboratory was analyzed. Students analyzed the tap water by at least three trials per each determination of total water hardness, individual calcium concentration and individual magnesium concentration. Student data from their exact experiments (as “Exact”) were compared with dependent calculation values (as “DCV”). Table 4 compares the results from student-developed exact experiments with dependent calculation values. Here, difference percentage was analyzed by the students at that time, and the t test and F test were evaluated by the instructor. The two-tailed t test showed no differences in the average of each metallic determination between the results from studentdeveloped exact experiments and the dependent calculation values for the Ca-B, Ca-C, Mg-C, and Mg-D methods. The Ca-A method average did differ significantly ( p < 0.05). The one-sided F test revealed that the precision of the Ca-A and Ca-C methods from student-developed experiments was significantly better than that of dependent calculations ( p < 0.05). In fact, the precision of the Mg-C and Mg-D methods is significantly worse ( p < 0.01). Based on the two-tailed t test, student-developed experiments for the five metallic determination methods are quite feasible. To further evaluate the feasibility of student-developed exact experiments, the same tap water was also examined by

UV–vis spectrophotometry by the instructor. Students’ exact experimental data (as Exact) were compared with instructor’s spectrophotometric data (as Spec), which is shown in Table 5, comparing the different analytical methods. Here, different percentage, and the t test and F test were evaluated by the instructor. The two-tailed t test showed there were no differences in the average between the result from student-developed exact experiments and the data from spectrophotometry. The one-sided F test showed there were no differences in the precision between the Ca-A, Ca-B, and Ca-C methods from student-developed experiments and the instructor’s spectrophotometry. However, the Mg-C and Mg-D methods were significantly worse than the instructor’s spectrophotometry ( p < 0.05). Based on the two-tailed t test, five student-developed independent-protocol experiments had a high feasibility for individual metallic determinations. Effects on Student Learning To better analyze any effects on student learning, data were organized into these five categories: searching the literature; team discussions; designing the experiments; testing trial experiments and performing exact experiments; and inquiry-based learning. Further discussion about these categories, the qualitative analysis of students’ feedback, and the implications of these effects are described below. Summary of Effects Students were asked to provide feedback about this activity that was part of the process of designing these experiments. The following synopsis is based on students’ written reflections to open-ended questions.

1. Literature searches: Students had difficulty reading the literature in English, and needed senior students to help them. In the search process, students learned more chemistry and information analysis.

2. Team discussions: Students felt good about the discussions and knowing others’ opinions. Discussion facilitates information exchange and friendship.

3. Designing experiments: Students thought that designing experiments involves many things, even minor details. Designing an innovative experiment is challenging and interesting. Some students felt confident, while others did not. Students spent more time on thinking about designing their own procedures.

4. Testing and performing experiments: Students gained confidence if their experimental results were similar to others, and the greatest gain came from students’ own original designs. Students were apprehensive at the beginning, yet they felt happy after performing their experiments.

5. Inquiry-based learning: Students acquired chemistry and nonchemistry knowledge during this activity. After finishing this activity, students knew what scientific inquiry was and how inquiry-based experiments are practiced.

Qualitative Analyses Student feedback was coded using PR (positive response), NR (negative response) and PNR (combination of positive and negative responses), and all are presented in the online supple-


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ment. Student learning impacts revealed that positive responses toward designing experiments, student discussion, testing trial experiments and inquiry-based learning were in the overwhelming majority. Negative responses about performing exact experiments were more than half. Positive responses concerning the literature search and discussions were almost equal to the negative responses. Implications Based on the evaluations summarized above, student achievement focused not only on chemistry and nonchemistry knowledge, but also on inquiry-based learning, especially in designing experiments. Team discussion in laboratory instruction is important because it facilitates information exchange for developing experiments. Students’ feelings toward testing and performing procedure-open experiments were diverse. In the affective domain students’ experience is various and complicated. This project is quite similar to a scientist’s experience in exploring the unknown world. This activity is worthwhile in creating an opportunity for undergraduate students to realize and practice scientific inquiry. Therefore, many laboratory instructors understand and emphasize the need to integrate inquiry-based learning into chemistry labs to challenge students’ ideas. Moreover, we postulate that the more open the level of the activity (e.g., access to sufficient chemicals and equipment), the more students will learn. On the other hand, according to students’ feedback about the literature search, this activity may be better suited to an analytical chemistry lab than in a general chemistry lab. Conclusions This study attempted to create a challenging opportunity for general chemistry students through mimicking the scientific research process to solve a water quality problem concerning individual concentrations of calcium and magnesium in water samples. We found that the general chemistry students were able to develop their own experiments to solve real-world, multivariable problems using skills from the practice of inquirybased learning. Based on experiment evaluations and positive student responses, this study provides a good example of the student-developed experiment processes—(i) literature search and discussion, (ii) designing, testing, and evaluating their own trial procedures, and (iii) developing, performing and evaluating their own exact experiments. This study also offers a useful way to evaluate the feasibility of student-developed experiments by statistical analysis using error percentage and difference percentage values, the t test, and the F test. In addition, the five independent-protocol experiments that students developed for determining individual calcium and magnesium concentrations in water can be used as real-time manipulative experiments for general chemistry and analytical chemistry laboratories. During this activity students’ circumstances in developing their experiments and their achievements can be described as follows: Students have not found that the literature describing step-by-step complexometric procedures can provide a design for their experimental procedures. Students submitted eleven methods containing five calcium and six magnesium determinations without describing detailed procedures. Most student methods used EDTA as a complexometric titrant and applied precipitating agents as masking agents. Statistical analyses indicated that student-designed trial procedures had five independent 512

protocols with feasibility rankings of either “high” or “middle”. Students used the five methods as templates for developing their exact experiments to quantitatively analyze tap water. Statistical analyses indicated that students succeeded in developing five independent protocols for individual metallic determinations (see the online supplement). Positive student responses towards designing experiments, student discussion, testing trial experiments, and inquiry-based learning were the overwhelming majority. Students’ negative responses towards performing exact experiments were more than half, whereas their positive responses towards literature searches and discussion were almost equal to the negative responses. After finishing this activity, students knew what scientific inquiry was and how inquiry-based experiments were practiced. This activity is worthwhile in creating an opportunity for undergraduate students to realize and practice scientific inquiry while learning chemistry content. Acknowledgments The authors thank the National Science Council of Taiwan for financial support (grant 94-2511-S-018-012); the chemistry major students at NCUE in Taiwan who participated in this activity during the spring 2006 semester; three anonymous reviewers; Ching-Han Hu for helpful suggestions; and Ruei-Ying Tsai for enthusiastic assistance. Literature Cited 1. Greco, T. G.; Rickard, L. H.; Weiss, G. S. Experiments in General Chemistry: Principles and Modern Applications, 8th ed.; Prentice Hall: Upper Saddle River, NJ, 2002; pp 187–192. 2. Wentworth, R. A. D. Experiments in General Chemistry, 7th ed.; Houghton Miffin Company: Boston, 2003; pp 225–235. 3. de la Camp, U. ; Seely, O. Complexometric Ca Determination Web Page. http://www.csudh.edu/oliver/che230/labmanual/ calcium.htm (accessed Jan 2009). 4. Akhtar, M. J.; Kerber, R. C. Complexometric Titration of Calcium in Antacids. http://www.ic.sunysb.edu/Class/che134/susb/ susb017.pdf (accessed Jan 2009). 5. Gregory, R. Determination of Copper and Nickel by Complexometric Titration. http://www.ipfw.edu/chem/321/Edta.pdf (accessed Jan 2009). 6. Selco, J. I.; Roberts, J. L., Jr.; Wacks, D. B. J. Chem. Educ. 2003, 80, 54–57. 7. Arnold, R. J. J. Chem. Educ. 2003, 80, 58–60. 8. Novick, S. G. J. Chem. Educ. 1997, 74, 1463. 9. Weigand, W. A. J. Chem. Educ. 2000, 77, 1334. 10. Yang, S.-P.; Tsai, R.-Y. J. Chem. Educ. 2006, 83, 906–909. 11. Determination of Calcium–Magnesium by EDTA Titration. http://www.sjsu.edu/faculty/chem55/55mgca.htm (accessed Jan 2009). 12. Harris, D. C. EDTA Titration of Ca2+ and Mg2+ in Natural Waters. http://bcs.whfreeman.com/exploringchem3e/content/cat_060/ experiments.pdf (accessed Jan 2009). 13. Kennedy, J. H. Analytical Chemistry: Practice; Harcourt Brace Jovanovich: San Diego, CA, 1984; p 77. 14. Comprehensive Analytical Chemistry, Vol. IC; Wilson, C. L., Wilson, D. W., Eds.; Elsevier: New York, 1962; p 71. 15. Rudd, J. A., II; Greenbowe, T. J.; Hand, B. M.; Legg, M. J. J. Chem. Educ. 2001, 78, 1680–1686.


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29. Tribe, L.; Kostka, K. J. Chem. Educ. 2007, 84, 1031–1034. 30. Powell, J. R.; Tucker, S. A.; Acree, W. E., Jr.; Sees, J. A.; Hall, L. H. J. Chem. Educ. 1996, 73, 984–985. 31. Tucker, S. A.; Acree, W. E., Jr. J. Chem. Educ. 1994, 71, 71–74. 32. Reeve, A. M. J. Chem. Educ. 2004, 81, 1497–1499. 33. Gravert, D. J. J. Chem. Educ. 2006, 83, 898–901. 34. Berry, D. E; Fawkes, K. L.; Chivers, T. Chem. Educat. 2001, 6 (2), 109–111. 35. Graham, K. J.; Schaller, C. P.; Johnson, B. J.; Klassen, J. B. Chem. Educat. 2002, 7 (6), 376–378. 36. Schwab, J. J., Brandwein, P. F., Eds. The Teaching of Science; Harvard University Press: Cambridge, MA, 1962; Chapter 1. 37. Herron, M. D. School Review 1971, 79 (2), 171–212. 38. Chen, S.-N. Quantitative Analysis, 11th ed.; San-Min Books: Taipei, Taiwan, 1993; p 138.

Supporting JCE Online Material

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Student-developed experimental procedures


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Using Student-Developed, Inquiry-Based Experiments To Investigate

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