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Asia-Pacific Forum on Science Learning and Teaching, Volume 19, Issue 2, Article 3 (Dec., 2018) |
In this study, a quasi-experimental design, involving randomly assigned experimental (EG) and control (CG) groups were employed. Both of EG and CG groups were taught the same topic investigating the effects of the presence of catalyst and solutions with different concentrations on the rate of reaction. Both groups were taught by the students' regular chemistry teacher. This teacher has been teaching chemistry for more than 20 years. In this case, the EG was taught on the effect of concentration and catalyst on the rate of reaction using CBGCEs. On the contrary, the CG was taught using the usual curriculum with more polluting and hazardous experiments.
The sample for this study consisted of 100 17 and 18 years old Form Five (equivalent to grade 11) students from two different intact classes in a school. Students from the two different classes were randomly assigned into two groups: EG consisted of 50 students with 28 female and 22 males, and similarly CG has 50 students with 31 females and 19 males. All the 100 students from both groups participated in the study because the researcher does not have any authority to eliminate any one of them. As such intact group sampling approach was used in this study.
The rate of Reaction Test (RORT)
The rate of Reaction Test consisted of 20 multiple choice questions. All the 20 questions assessed students' understanding about the effects of catalyst and effects of concentration on the rate of reactions. Questions 1,2,3,4,6,9,10,17,19 and 20 in the RORT assessed the understanding on the effects of concentration on the rate of reaction while questions 5,7,8,11,12,13,14,15,16 and 18 in RORT tested the understanding on the effects of catalyst on the rate of reaction. The questions in RORT are past years' examination questions. The teachers from different parts of the country gathered in one place and involved in designing the questions. The designing process were closely monitored to ensure the validity and reliability of the questions. For all the questions in RORT, students were provided with four choices. The students were required to choose the best possible answer. The correct choice was awarded 1 point, and the incorrect answer was not given any points. An example of a multiple choice question in RORT is presented in Figure 1.
Which of the following is not a characteristic of a catalyst?
A. Catalysts is specific in its reaction
B. A catalyst influence the quantity of product of a reaction
C. The chemical property of catalysts remains unchanged at the end of the reaction
D. Only a little amount of catalyst is needed to influence the rate of reaction.
Figure 1: An example of question in RORT
Issue-Based Questions
Issue-based questions are questions that were designed based on everyday issues that deal with concentration and catalyst. A group of five chemistry teachers collaboratively involved in designing the two questions. Firstly, the teachers brainstormed and identified aspects to be assessed in relation to the given context. Upon reaching to an agreement, the questions were formulated. The two questions were further discussed and refined till final questions were designed. For concentration, students required to resolve the issue why Clorox (common name for bleach) without mixing in water, decolorizes the cloth promptly compared to Clorox which is mixed with water (Figure 2). For catalyst, students were given a situation what happens if yeast was not included in baking a cake and they were asked to compare the situation with presences of yeast as shown in Figure 3.
Figure 2: Issue-based question on the effect of concentration
Figure 3: Issue-based question on the effect of catalystThe questions were given to both experimental and control group students after they performed the experiments.
Interview Questions
The interviews were performed with both experimental and control groups after the treatment. A total of five interview respondents were identified using purposive random sampling method. The interview responses were used to obtain further insights into students' understanding of the effects of concentration and catalysts on the rate of reaction. Each interview session was completed between 45 to 50 minutes. The responses were transcribed in the entity. Following are the interview questions:
What do you know about concentration?
Can you explain how does concentration affects the rate of reaction?
What do you know about catalyst?
Can you explain how does a catalyst affect the rate of reaction?
A pilot study involving 45 Form Five students and two experienced chemistry teachers from a neighboring secondary school was performed to evaluate the reliability and validity of rate of reaction test (RORT) and issue-based questions and also to validate the CBGCEs. Both the participating teachers have more than twenty years of experiences teaching Form Four and Form Five chemistry. The teachers commented that multiple choice questions in RORT and the open-ended issue-based questions encompass the requirements of curriculum specification. The questions possess reliable content validity. The teachers were also noted that language used was simple, understandable and appropriate to the level to the students. For the multiple choice questions in the RORT, a KR-20 value of 0.968 obtained from the pilot study, indicates that questions in test possess high internal consistency.
The CBGCEs were validated to check on the appropriateness of the experiments, the language used in experiments, availability of the apparatus and materials to conduct the experiments and feasibility to conduct the experiments. The teachers identified that CBGCEs was feasible to be implemented, the materials and apparatus were readily available. The language used in presenting the experiments were clear. The teachers proposed that CBGCEs should be implemented replacing the current polluting and dangerous experiments done by the students.
Conventional Curriculum
The entire five lessons for the control group started with the teacher posing questions to retrieve students' prior knowledge. During the first lesson, questions were also asked to ensure that the students have basic ideas about the effect of concentration and catalyst on the rate of reaction. This information was helpful for the teacher to decide on the content of the lessons. Once the prior knowledge has been ruled out, the teacher continued the lessons, asking the students to refer to the textbook and read the steps and procedures involved in performing the experiments. Four different experiments were performed in all the four lessons. During lesson two, the reaction between sodium thiosulphate solutions with different concentration and sulphuric acid was investigated. Subsequently, in lesson three, the reaction between different acids (hydrochloric acids, sulphuric acids and ethanoic acids) with sodium thiosulphate solutions; lesson four decomposition of hydrogen peroxide with the presence and absence of the catalyst [manganese(IV) oxide] and in the fifth lesson, experiment on decomposition of hydrogen peroxide with different quantity of catalyst [(manganese (IV) oxide] were investigated. The experiments in lesson 2 and 3 focused on learning about the effect of concentration and 4 and 5 on the catalyst. Before allowing the students to conduct the experiments, in each lesson, the teacher warned the students about the harmful effects of the chemicals, and they have to be careful in handling the chemicals. The students performed the experiments closely following the procedures included in the textbook. After completing the experiments, the observations and findings of the experiments were discussed with the teacher dominating the lesson. At the end of the lesson, students were asked to respond to the issue-based questions.
Context-Based Green Chemistry Curriculum
Similar, to the control group, the lessons for the experimental group started with the teacher posing questions to retrieve the students' prior knowledge and to identify the level of students' knowledge on the effect of concentration and catalyst. Upon retrieving the prior knowledge, each lesson began with providing contexts relevant to the chemistry concept embedded in each particular lessons. The contexts which are relevant to the students' everyday activities permitted the students to envision on the practical applications of the concepts. For the first lesson, the teacher used orange juice with different concentrations to explain about concentration. The teacher presented three cups of orange juice with different concentrations; the students were asked to consume the juices and identify the differences in the taste of the juice. The teacher raised the question why do you think the diluted juice tasted lighter? The teacher explained further that the lighter taste is because of a number of particles per volume of juice in lesser in diluted juice. The juice is concentrated because a higher number of particles and the richer taste also results from the higher number of particles. Once the students have internalized the meaning of concentration students were asked to investigate the reactions between the different mass of chalk powder and vinegar. The investigation began with marking sign 'X' on a piece of white paper. Conical flask was placed on top of the 'X' sign. Firstly, 0.02g of chalk powder was placed into the flask, and 10mL of vinegar was mixed to the powder. The time taken for the sign 'X' to disappear was noted. The same investigation was repeated with a different mass of chalk powder. After completing the investigation, students required to write a balanced chemical equation describing the reaction; plotting graph time taken for the sign 'X' to disappear versus the mass of chalk powder; calculate the rate of reaction (g/time taken) and explain how concentration affects the time taken for the sign 'X' to disappear. Based on the explanation given by the teacher about orange juice prior to the investigation, the students explained concentrated chalk powder reacts faster with vinegar because it has a higher number of particles. The teacher explained further when there are more particles; there is more tendency for more collision and effective collision between vinegar and chalk particles. Effective collisions resulted in the reaction.
The second lesson focuses on teaching how the concentration of hydrogen ions in solutions changes the rate of reaction. For this purpose acidity level of 10mL of orange juice, lemon juice and vinegar was tested using red cabbage juice paper. Orange juice, lemon juice, and vinegar were later mixed with baking soda. For this purpose, a burette was filled with water and inverted over a basin containing water. The water level in the burette was adjusted, and the initial burette reading was recorded. 2g of baking soda was added to a conical flask and mixed with 50mL of vinegar. A delivery tube with a rubber stopper was inserted into the mouth of the conical flask, and the end of the delivery tube was inserted below the burette. The drop in the water level of the burette is recorded at 30 seconds intervals. The experiment was repeated replacing vinegar with lemon and orange juice. The differences in the volume of water in burette indicate the volume of carbon dioxide gas released from the experiment. The students were asked to observe the reactions and record the findings. The teacher later explained the concentration of hydrogen ions in these three substances are different. More acidic substances are concentrated with hydrogen ions. In other words, a number of hydrogen ion particles are more in more acidic solutions as such more effective collisions that result in reaction expected to happen.
In the third lesson, in introducing catalyst, the teacher presented two cups filled with the same volume of water added with salt. One of the cups was continuously stirred, and the other one was just left on the table. Teacher-related the action of stirring with the presence of a catalyst. The explanation also includes information on activation energy. Students applied the conceptions about catalyst and investigated the reaction between hydrogen peroxide solution and baking soda without the presence of a catalyst and repeated the experiment with the presence of biodegradable detergent as a catalyst. Similar, to lesson 2, in lesson 3 students prepared a burette filled with water and inverted in a basin. In a conical flask 10ml of hydrogen peroxide was added with 1 drop of detergent solution. Later 5g of baking soda was added to the mixture. A delivery tube was placed at the mouth of the conical flask, and later it was fixed to the bottom of the burette. The drop in the volume of water in the burette was recorded at the interval of 30 seconds. The investigation was repeated with adding detergent. At the end of the lesson, students were asked to write a chemical equation on the decomposition of hydrogen peroxide; plot a graph on volume of gases versus time, and explain how catalyst influences the reaction. In explaining the reaction students able to indicate with the presence of a catalyst the reaction happens in a different pathway with lower activation energy. When the activation energy is lower, more collisions tend to reach the energy required. This resulted in effective collisions for the reaction to happen.
In the fourth week, the teacher presented two cups filled with the same volume of water and sugar. Both cups were stirred. This time, one cup was stirred using one glass rod, and the other cup was stirred using two glass rods. The glass rods presences the catalyst and number of glass rods indicate the quantity of catalyst. Once the students have understood the concept of catalyst, they were asked to investigate the reaction between hydrogen peroxide and baking soda with the presences different quantity of biodegradable detergents. The investigation was performed similarly as in lesson 3. They were asked to plot graph volume versus time for all the three repetitions of the experiment with the different amount of detergent on the same graph; interpret the graph and explain how different amount of catalyst affects the rate.
The four CBGCEs introduced began with a context that students usually encounter in their everyday living. The conceptions of how concentration and catalyst work was forwarded using these contexts. Once the students have clear conceptions of catalyst and concentration than the students performed investigations using experiments developed based on green chemistry principles, in performing these experiments, students learn chemistry inherent to catalyst and concentration on the rate of reaction. In answering the questions provided at the end of the experiments and discussion of the observations and findings of the experiments, provided students a better understanding of the concepts investigated.
Two different types of data were collected in this research to determine the understanding of students on the effects of concentration and catalyst on the rate of reaction. Qualitative findings were used as the primary data to answer the research question. Quantitative findings were used to substantiate the qualitative outcome. In the next section, the information on how the quantitative and qualitative data were analyzed is provided.
Qualitative data
Qualitative content analysis method was employed to analysis both open-ended issue-based questions and interview responses. Students' answers to the issue-based questions were explicitly examined for certain words and phrases that describe the understanding of the concepts. In Table 1 examples of good and average responses provided for the issue-based question on the effects of concentration are presented. The emerging themes are presented in italic font.
Table 1 Examples of good and average responses for the effects of concentration
Average understanding
Good understanding
Adding water will result in dilution of Clorox. The reaction with diluted Clorox will be slower because diluted Clorox is less concentrated. The diluted Clorox might remove the color on the cloth, or it will take longer for the cloth to be bleached.
Clorox will be diluted with adding water. The number of particles per unit volume in Clorox without water is higher, and it is more concentrated than Clorox with water. It will react with the color on the cloth and bleaching happens. The Clorox which added with water does not bleach or bleach slower because a number of particles per unit volume are less.
The common themes emerged from both responses above are faster/slower reactions; concentrated/less concentrated; particles per unit volume; bleaching (removing color). Both responses reflect that students have acquired the understanding that concentration influences the rate of reaction as both students indicated that bleaching happens at a different rate in diluted and non-diluted Clorox. However, more specific themes 'particles per unit volume' and 'react with the color' that emerged shows that this particular student acquired an accurate understanding of the concept. Similar to the open-ended issue-based questions, content analysis was used to examine interview responses to identify specific themes. The themes derived from the responses were: increasing/decreasing rate; frequency/effective collision; positive/negative catalyst. Table 2 shows examples of responses with a good and average understanding of the effects of catalyst on the rate of reaction and the emerging themes are presented in italic.
Table 2 Examples of responses with a good and average understanding of the effects of catalyst
Average understanding
Good understanding
Catalyst plays an important role in increasing the rate of reaction. It increases the frequency of collision, and this automatically increases the rate.
The presence of a catalyst, I mean positive catalyst enable the reaction go through an alternative path with lower activation energy. More collisions could overcome the lower activation energy. As suchfrequency of effective collisions increase, and rate of reaction also increases.
Quantitative data
Quantitative data collected were analyzed using SPSS (Statistical Packages for the Social Sciences) with the level of significance at 0.05 (p>0.05). The post-test results of the RORT were compared using independent sample t-test to compare the mean of traditional teaching method (control group) and context-based green chemistry experiments (experimental group). Following Trochim's (2006) suggestion, to ensure the students from both EG and CG have a similar level of chemistry knowledge prior to the treatment, an independent t-test was performed using the results of chemistry class test. The findings of the independent t-test analysis revealed that both group students are at the similar level prior to the treatment.
