Exploring the use of context-based green chemistry experiments in understanding the effects of concentration and catalyst on the rate of reaction

This section begins with illustrating students' understanding of the effects concentration on the rate of reaction using qualitative open-ended and interview responses. Subsequently, students understanding the effects of catalysts will be articulated similarly. Quantitative findings were employed to substantiate the qualitative findings.

Understanding the effects of concentration

The analysis of interview responses

The analysis of interview responses obtained reflect that students from both groups have the knowledge about concentration and how concentration affects the rate of reaction. The differences emerged between these groups are that experimental group able to explain more scientifically. This shows that the experimental group students understand the functions of concentration from the particle level. On the contrary, the control students' responses appeared more like a layman's description of concentration and how it affects the rate. Following are excerpts of interviews responses obtained from control and experimental group students for the question "What do you know about concentration?".

Table 3 Responses to question "what do understand about concentration?" from experimental and control group students

	Control Group Responses		Experimental Group Responses
S1	Concentration is something that can make the reaction happen faster.	S4	Concentration is a number of particles per unit volume in the aqueous solution. A more concentrated solution has more number of particles.
S2	Concentration is the amount of reactant in the solution.	S5	Concentration is the quantity of solute that dissolves in 1dm3 of the solution. Like when salt dissolves in water to form a salt solution. Salt is solute and water is solvent. The salt solution is a mixture of water and salt.
S3	Concentration is the factor that that can change the rate of reaction.	S6	Concentration influences the rate of reaction. It is about a number of particles in the solution.

Analysis of responses given by control group student shows that two students (S1 and S3) perceived concentration is something got to do with the rate of reaction. Another student (S2) is in the understanding; concentration is the amount of reactant in a solution. The answer given by S2 seems to be more appropriate than S1. Rather than directly linking concentration with the rate of reaction, S2 said that it is about the amount. However, in indicating the number of particles, S2 simply said an amount of reactant. These findings show that control group students somewhat have conceptualized 'concentration,' however, they have not reached the level of complete understanding. Experimental group students exhibited similar conceptualization about concentration whereby they said that concentration got to do with the rate of reaction. However, prior to linking concentration with faster or slower reaction, they have indicated concentration is the amount of particles per volume. In a concentrated solution, this amount is higher. Thus the reaction would be faster. To further, understand the students' knowledge of concentration and rate of reaction, the students were posed with the question "can you explain how does concentration affects the rate of reaction?" The responses were included in Table 4.

Table 4 Responses to the question "can you explain how does concentration affect the rate of reaction?" from experimental and control group students

	Control Group Responses		Experimental Group Responses
S1	When the concentration of the solution is high, it can change the rate of reaction. It makes the reaction fast.	S3	Concentration can affect the rate of reaction. When the concentration of the solution is high, the number of particles per unit volume is more. This will result in a higher frequency of collision between the particles in the solution.
S2	When the concentration of the solution is high, the rate of reaction will be faster. Because it will make the reaction faster and time taken will be shorter because the frequency of effective collision is higher.	S4	When the concentration of the solution is higher, the rate of reaction is also higher because the number of particle per unit volume is more. This makes the frequency of collision between the particles increases; as a result, the frequency of effective collision also increases.

The control group students unable to provide details linking the concentration and rate of reaction. Their understanding seems to be limited as they repetitively mentioned higher concentration would result in a faster reaction. S2 try to explain saying that time taken will be shorter as the frequency of effective collision is higher. However, information on how effective collision is related to rate is not given. The responses of experimental group students reflect that these group of students has the understanding, concentration is about amount particles. Higher amount particles per volume increase the number of collision between the particles. With the increase in the number of the collision, the frequency of effective collations that causes the reaction to happen increases as well.

The analysis of responses to the issue-based question

In Table 5 responses to the issue-based questions on the effects of concentration obtained from control and experimental group, students are presented.

Table 5 Responses of the control and experimental group students for the issue-based questions on the effect of concentration on the rate of reaction

	Control Group		Experimental Group
S1	In the Clorox without water, the number of enzymes presented is more compared to the Clorox mixed with water. More enzyme will break down and react to the color of the cloth. The color of the cloth will be bleached. The rate of reaction between the enzyme and the cloth is higher.	S4	Colour of the cloth bleaches when it directly poured because the concentration of Clorox is more compared to the Clorox which was mixed with water. When the concentration of Clorox is high, the number of particles per unit volume is more. So concentrated Clorox used to wash cloth react with the color of the cloth. When Clorox reacts with particles on the cloth, it will remove the color from the cloth.
S2	When Clorox is mixed with water, the concentration of the solution decreases. This causes the bleaching particles per unit volume to decrease. The frequency of collision between particles decreases. The frequency of effective collision also decreases. Thus, the rate of reaction decreases. Highly concentrated Clorox able to bleach due to the higher rate of reaction.	S5	When water is added to any substances, it will decrease the concentration of the solution. So when water is mixed with Clorox, the Clorox is diluted. The number of particles per unit volume is lesser. So when it used to wash cloths, the dirt will be removed at the same time it reacts with the color on the cloths.

Basically, in the responses obtained from the control group students, the themes, such as mixing with water resulted in the Clorox diluted; the concentration of Clorox is lesser when mixed with water; and reaction gets slower with lesser concentration appeared. These themes show that control group students unable to be very specific. They appeared more general in providing their description of the rate of reaction. Control group students acquired the understanding that when Clorox is mixed with water, it gets diluted, as such less concentrated. The experimental group students in their responses exhibited a similar kind of understanding. However, the experimental group students tend to be more specific in their answers. For instance, rather than simply saying concentration is higher or lesser, the students specifically mentioned that concentration in terms of the number of particles per volume. They further said that the particles react with the color of the cloth and thus bleaching happens. The discoloration happens when there is a collision between Clorox and color particles. As in concentrated solutions number of particles per volume is high frequency of collations increases as well.

Understanding the Effects of Catalyst on the Rate of Reaction

The analysis of interview responses.

In Table 6 excerpts of interview responses obtained from control and experimental group students for the question "what do you know about catalyst?" are presented.

Table 6 Responses to question "what do you understand about catalyst?" from experimental and control group students

	Control Group		Experimental Group
S1	The catalyst can make the reaction faster.	S4	The catalyst is a substance used to increase the rate of reaction and catalyst itself does not change chemically.
S2	Is a chemical that we use for faster reaction. At the end of the reaction, catalyst remains.	S5	A catalyst increases the rate, but the catalyst does not change chemically at the end of the reaction.
S3	The catalyst is a process where the reaction happens faster.	S6	The catalyst can make the reaction happen faster.

The responses show that both groups attained the understanding that catalyst is a substance that increases the rate without changing its chemical properties as the themes 'faster reaction' and 'remains the same' appeared in the all the responses. Excerpt of S3 from control group exhibited a misconception saying catalyst is a process. The responses in Table 6 shows that students from both groups have understood what catalyst is. In further probing their understanding of the functions of catalyst the question 'can you explain how catalyst effects the rate of reaction?' was asked. Some of the responses to this question are presented in Table 7.

Table 7 Responses from control and experimental group students to the question "can you explain how catalyst effects the rate of reaction?"

	Control Group		Experimental Group
S1	A catalyst increases the frequency of collisions. Increase in the frequency increases the rate of reaction.	S3	Catalyst creates a new path with a lower activation energy for the reaction to happen. The frequency of effective collation increases. The reactions that overcomes the activation energy is more.
S2	The catalyst causes the reaction to take place in a shorter time. This is because it will make reactants to produce product faster by increasing the frequency of effective collision. So this increases the rate of reaction.	S4	With having an alternative path, the number of particlesachieved the lower activation energy will be more and frequency of effective collision increases and rate of reaction also increase.

The theme, 'frequency of collision,' 'frequency of effective collision' and 'faster reaction' appears in the responses given by students from the control and experimental group. Appearances of the themes show that the students have acquired the understanding that in the presences of catalyst, the reaction happens in a shorter period because of more effective collision happens during the reaction. The themes, 'alternative path' and 'activation energy' reflects that experimental group students have attained the understanding that in the case of presence of a catalyst, the reaction occurred using a different pathway with lower activation energy. Experimental group students able to grasp with the alternative path, more effective collisions will result as many collisions manage to overcome the activation energy.

The analysis of the response to the issue-based question

The examples of responses provided by control and experimental group students for the issue-based question on the effects of catalysts on daily life activity is presented in Table 8.

Table 8 The answers provided by the experimental and control group students for the issue-based questions on the effects of catalyst

Control Group	Experimental Group
The bread Vikasni baked contains yeast while the bread baked by her sister does not have yeast. Yeast performs anaerobic respiration in the presences of glucose and produces carbon dioxide, ethanol, and heat. Carbon dioxide occupies the space in the bread forming air sacs in the bread causing it to rise and become fluffy.	Yeast as a positive catalyst in the baking of bread produces carbon dioxide. As a living organism, yeast undergoes respiration and releases carbon dioxide gas and heat. It makes the bread bake faster as well. Time taken to bake the bread without yeast is longer. With extra heat, the whole baking reaction took place using a shorter path with less activation energy.
This is because of the yeast used by Vikasni. It produces carbon dioxide in the presence of water. The respiration process produces more heat when more carbon dioxide is released. The carbon dioxide occupies the space and the dough rises. The heat causes the cake to bake faster.	Yeast is a catalyst for baking. It produces carbon dioxide gas and heat. Carbon dioxide rises the cake. However, the heat makes the reaction faster. With the yeast, an alternative route with a different pathway was created. This pathway has lower activation energy. More collision expected to overcome the activation energy to result in a reaction.

The analysis of the responses revealed that both group students managed to identify that yeast plays the role as a catalyst in the baking process. Both groups are also able to provide on how yeast functions as a catalyst in the baking process from the themes: carbon dioxide; heat; forming air sacs; and heat causes the bread to bake faster. The experimental group students exhibited scientifically defined understanding on the function of yeast in baking a cake. The themes such as alternative route; lower activation energy; and collision expected to overcome the activation energy emerged from the response reflects that ability of experimental group students to be more explicit in answering the questions.

Quantitative findings

A maximum total score for RORT is 20. The control group's mean score (M_con=9.14, SD_con=3.47) reported being lower than the experimental group's mean score (M_exp=12.90, SD_exp=3.13). The differences between the mean scores of both groups are reported to be significant [t(98)= -5.69, p<0.05]. The results show that the students from the experimental group were able to score higher on the RORT than the control group students. This shows that experimental group students' understanding of the effect of concentration and catalyst on the rate of reaction is far better with the mean differences of 3.76. This finding substantiates the qualitative findings obtained from interview and issue-based open-ended question analysis.