Using laboratory activities enhanced with concept cartoons to support progression in students’ understanding of acid-base concepts

The descriptive measures of the tests for the EG and the CG are given in Table 2. As seen from the Table 2, students’ mean scores of pretest were similar for the EG (M=23.37; SD=12.38) and the CG (M=25.18; SD=9.67). Independent t-test results towards pretest scores also indicated that there was no statistically significant difference between groups (t= 0.484, df=34, p=0.631). This reflects similar backgrounds of the both group students in respect to acid-base chemistry achievement before the intervention.

Table 2. The comparison of the pretest and posttest results of the groups in the ABAT

	Groups	N	Mean	SD	t	p
Pretest	Experiment	19	23.37	12.38	0.484	0.631
Pretest	Comparison	17	25.18	9.67	0.484	0.631
Posttest	Experiment	19	66.11	17.66	2.896	0.007
Posttest	Comparison	17	48.94	17.86	2.896	0.007

Because there were no statistically significant differences between the pretest results, the posttest results were compared via independent t-test and a statistically significant difference was found between the posttest scores of the EG (M=66.11; SD=17.66) and CG (M=48.94; SD=17.86) with respect to the chemistry achievement (t= 2.896, df=34, p=0.007). This means that there was a significant mean difference between the students in the EG and CG with respect to understanding of acids and bases.

Students’ pre-interviews conducted before the study and literature review give us some information about the students’ views and alternative conceptions related to acids and bases. Based on these data, we developed worksheets to remedy students’ ideas and to improve their understanding about the concepts. Table 3 shows percentages of students’ alternative conceptions before and after the intervention.

Table 3. Percentages of students’ alternative conceptions before and after the intervention

Alternative conceptions (AC)

Experimental Group

Control Group

Pretest (%)

Posttest (%)

Pretest (%)

Posttest (%)

1. In the formulas, species containing H are acids and species containing OH are bases

2. Acidic substances taste bitter and peppery

3. While acids are poisonous, bases are not

4. Acids burn and melt everything

5. Bases are composed of acids

6. The only way to test a sample whether it is an acid or a base is to see if it melts something

If we add Na metal into acidic solution, it; -

7. melts

8. burns

9. disappears

10. While aqueous solutions of ~~the~~ acids conduct electricity, bases are not

11. Electrical conductivity of all acids and bases are the same

12. We can determine the strength of an acid or base by using litmus paper

From implementation of the ABAT in pretest, twelve alternative conceptions were identified. While the percentages of students’ alternative conceptions in pretest ranged from 11% to 63% in the EG, that of the students in the CG ranged from 6% to 65% (Table 3). The students in each group held almost the same alternative conceptions in pretest at about the same percentages. The alternative conceptions obtained from the study support previous studies, which suggested that students at a variety of levels hold similar alternative conceptions (Bradley & Mosimege, 1998; Demircioğlu, Ayas & Demircioğlu, 2005; Nakhleh & Krajcik, 1994). In the EG, during the intervention, worksheets enhanced with concept cartoons were used to remedy students’ alternative conceptions identified in the pretest and pre-interview. Examination of the posttest results suggested that the EG students had fewer alternative conceptions after instruction. For example, the students in EG had completely corrected the following two alternative conceptions in the posttest: (i) Acidic substances taste bitter and peppery; (ii) Bases are composed of acids (Table 3). However, in the CG group, all of these alternative conceptions were retained.

Two of the alternative conceptions held by the most students before the implementation were “while the acids are poisonous, bases not” and “acids burn and melt everything”. These have also been common in related literature (Demircioğlu, Ayas & Demircioğlu, 2005; Özmen, Demircioğlu & Coll, 2009). While the former was held by 58% of the EG students and 65% of the CG students in pretest, these ratios were 32% and 47% in posttest. The latter showed a decrease from 63% to 11% from pretest to posttest for the EG students and from 59% to 29% for the CG students. In the present study, worksheet A was used to overcome these alternative conceptions in EG. As seen in Appendix A, it consisted of a concept cartoon aiming to activate students’ preconceptions, and practical activities that gave students the opportunity to actually experience the effects of different indicators on some acids and bases found in laboratory and examples of acidic and basic substances used in daily life; and to taste some weak acidic and basic substances. From the practical activities, the students were able to see that some weak acidic and basic substances could be tasted. As a result, they could see that acids did not burn and melt everything and that not all acids were poisonous. After students completed the practical activities, they were asked to discuss the results of the activities and to compare with their pre-conceptions. Based on this, most of the EG students dispelled their alternative conceptions. That the practical activities are effective in remedying alternative conceptions related to acids and bases is also reported by Özmen, Demircioğlu and Coll (2009). They used practical laboratory activities in teaching of acids and bases and found that such activities increased students’ understanding. Of course, the CG students also dispelled their alternative conceptions to a certain extent. But Nevertheless, teacher in the CG did not use worksheets including concept cartoons and alternative conceptions. For this reason, the EG students became more successful than the CG ones in remedying alternative conceptions.

One of the alternative conceptions was that “in the formulas, species containing H are acids and species containing OH are bases” (see Table 3, AC-1). This was held by 63% of the EG students in pretest and 21% in posttest, while these ratios were 47% in pretest and 24% in posttest for the CG students. This is also a common alternative conception in the literature (Acar Sesen & Tarhan, 2011; Demircioğlu, 2009; Demircioğlu, Ayas & Demircioğlu, 2005). In all levels, students believe that if a matter contains H, it is an acid; if a matter contains OH, it is a base. We think that there may be a few reasons for such erroneous ideas. One of them may be poor explanations and examples given by teachers while describing the theories of acids and bases in their courses. Another one may be microscopic nature of these concepts. In this study, it was used species containing OH in their formula such as CH3COOH, containing H such as NH3, H2O, CH4 and containing neither H nor OH such as CO2, MgO in the worksheet A and E in order to remedying the AC-1. After discussing the acidic and basic properties of these species, the teacher emphasized that aqueous solutions of some species are not basic although they contain OH group (for example, CH3COOH). Besides, aqueous solutions of some species are basic although they contain H (for example NH3); some species are not acidic although they contain H (for example, H2O and CH4); and aqueous solutions of some species are acidic although they do not contain H (for example CO2). These examples show students that having H in the formula is not a unique criterion for determining acidic and basic properties of the solutions of these species. Students have already seen this truth during the activities. Teachers often think that some concepts are very simple and students learn them easily when they are explained in detail. We know from the literature that traditional approaches, especially verbal explanations, are not effective for remedying students’ alternative conceptions because of their resistant nature to change (BouJaoude, 1991).

Another alternative conception was that “the only way to test a sample whether it is an acid or a base is to see if it melts something” (see Table 3, AC – 6) and this is most common in the literature (Özmen, Demircioğlu & Coll, 2009). This was held by 42% of the EG students in pretest and 5% in posttest; and for the CG students, these ratios were 53% in pretest and 12% in posttest. In the study, the worksheet A and B struggled with AC-6 in EG. For this aim, in worksheet A, students tried to test acidic and basic properties of some matters by using litmus paper, pH paper, red cabbage, phenol phatelyn, tasting, and slippery feel. Also, in worksheet B, students had opportunity to see the effect of different acids and bases on various matters. For example, in one of the activities, a piece of meat was put into hydrochloric acid, nitric acids, ammonia and sodium hydroxide solutions, separately. After waiting for a while, students observed the change on the surface of the meat. In another activity found in worksheet B, students dropped lemon juice, vinegar, and soapsuds onto their hands and observed that these acids and bases did not affect their hands. These two activities showed students that while some of the acids and bases affected the matters, some others did not. This observation says us that whether a sample melt matters or not is not only way to classify it as acidic or basic. Based on these activities, most of the students in EG dispelled their alternative conception (see Table 3, AC – 6).

Another alternative conception was that “we can determine the strength of an acid or base by using litmus paper” (AC – 12).This isdifferent from others. As follows, AC – 12was held by 11% of the EG students and 6% of the CG students in pretest, and these ratios were 21% and 35% in posttest, respectively. The results show that there is an increase in ratios of the AC – 12in both groups from pretest to posttest. These increases in the ratios are amazing for us. Because, worksheet E is exactly about the determination of the strength of acids and bases via pH paper and students made some activities by using pH paper. And also, AC – 12 was already located in the concept cartoon section of the worksheet E and discussed in the groups. In the study, students in the EG also used litmus paper to determine acidic and basic properties of matters in worksheet A and B. For this reason, a number of students in this group may think that they could use litmus paper instead of pH paper to determine the strength of acids and/or bases. On the other hand, the CG’s students also had AC – 12 and its ratio increased from pretest to posttest. Similarly, the CG’s teacher informed her students that litmus paper was used to test acidic and basic properties of matters and then made some simple testing activities. Although she talked about the pH paper, students did not make practical activities by using it. Therefore, this might have caused such a view that we could determine the strength of an acid or base by using litmus paper.