CHAPTER 5 RESULTS SHOWING SCOPE AND QUALITY OF RESEARCH ON
7.6 SUMMARY AND DISCUSSION
It is difficult to encapsulate this difficulty in terms of the original research findings, but the propositional statements reveal the missing idea of a reaction between ions are water, leading to the description as given above. The difficulty has been shown in different German and Spanish cohorts, but the description given here needs to be confirmed, it is classified at Level 3+, being only partially established. Schmidt’s data also shows that there was a close relationship between this conception and that for predicting neutrality (or otherwise) of the titrations between corresponding acids and bases, described as Difficulty P16 in Section 7.4.1.2.
As in the previous chapter, the majority (nearly 70%) of the difficulties identified in this chapter confirm a lack of integration of empirical macroscopic observations into student conceptual frameworks. This is shown by 19 difficulties: P1 to P18 and P25. The evidence of such widespread difficulties, sometimes among senior students, suggests that chemistry education is becoming too theoretical and decontextualised. An advantage of teaching macroscopic observations through a study of acidic, basic and neutral household products could be to put chemistry in context, thereby relating it to everyday life and fostering more realistic understanding of safety issues (see P1 to P4). Furthermore, Furió-Más et al. (2005) found little evidence of textbooks incorporating macroscopic acid-base behaviour as an introduction to theoretical models, although “this is the problem that the Arrhenius and Brønsted theories must solve” (p 1353). It is therefore likely that students’ theoretical ideas have not been well grounded in empirical evidence. For example, the explanation of hydrolysis should be driven by observations of trends in neutral and non-neutral solutions of salts. Both Difficulties P25 and P26 show this is not so, and students are learning facts and explanations in isolation.
Furthermore difficulties with salts, (P15 and P25) could be due to an overemphasis on the theoretical Brønsted model, wherein salts as products of neutralization reactions are irrelevant.
Two categories of difficulties revealed in this chapter indicate problems with more fundamental chemistry than acids and bases. To be specific, classes of substances characterized by properties (P8 to P11) and the nature of the neutralization reaction (P19 to P22) can be seen as threshold concepts (Meyer & Land, 2006; Perkins (1999; 2006a; 2006b), in that they underpin, and are essential pre-requisites for learning higher level concepts. According to these authors threshold concepts are transformative and integrative, enabling a student to understand the subject discipline in a new and possibly irreversible way. Moreover, they are frequently troublesome. In particular, the notion of chemical change has been well documented as problematic (Johnson, 2002). However, according to Land et al. (2006), mastering threshold concepts takes time and repeated engagement with the concept from several perspectives. In this regard, de Vos and Verdonk’s articles (1985a; 1985b; 1986; 1987a) show a sequence of conceptual conflict strategies appropriate for revisiting the idea of chemical change in a variety of contexts. It follows that the context of acid-base chemistry could also provide similar potentially transformative points, which curriculum planners can exploit in order to enhance understanding of the nature of chemical change. To this end, acid-base substances can be used to learn classification through characteristic properties, such as in the sequence used by Solomonidou and Stavridou (2000) and the new substances produced and the energy changes could be used to show chemical change.
More difficulties had been identified in this chapter than in the previous chapter. However, only about a quarter of difficulties have been thoroughly researched to give an established description at Level 4 which is a smaller proportion than was found in Chapter 6. Therefore, it appears that not only do students have more difficulties with acid-base properties than with the actual species, but also researchers have not gained as much insight into these difficulties.
Research practitioners should, once again, take note of difficulties where further research is needed. For example, there is very little known about how students conceive the function of indicators (P13 and P14) or about the conception that acid and base consume each other (P22).
Both these difficulties are merely suspected but have considerable impact on future learning.
Difficulties with emerging descriptions include the concept students have about heat of neutralization. In this regard, the research for P17 is only vague because we do not know whether they are unaware of any energy changes, or whether they think heat is absorbed.
Numerous other difficulties have Level 3 descriptions. These partially established difficulties need further studies, either to clarify or confirm descriptions in other contexts. In particular, the difficulty which students have identifying acidic and basic characteristics (P8) has been reported frequently, yet still has an extremely vague description. It remains to be seen whether the research community rises to the challenge of investigating these more abstract ideas of acid- base properties and processes, to achieve more Level 4 difficulty descriptions.
For the eight difficulties with Level 4 descriptions, further research merely showing the existence of this conception in yet another student population is now largely redundant. We know the conception, we know it exists; we need to change the focus of research, perhaps to a study like Chiu’s (2007) to show prevalence across ages. In this chapter Level 4 difficulty descriptions arose in two ways. Firstly, single sustained research projects could lead to Level 4 difficulty descriptions (P16 and P20.2) or, as in the previous chapter, the remainder of the Level 4 descriptions were derived through critical analysis of results combined from individual research projects. In some cases the aggregate of work on a difficulty has already been recognised. For example see Pinarbasi (2007) who cites work concerning the dangers (or lack thereof) generally attributed to acids and bases. However a valuable aspect of this critical analysis is its highlighting the combined evidence leading to other previously unrecognised Level 4 descriptions seldom mentioned in literature reviews, such as Difficulty P20.1 concerning the idea of indicators assisting with neutralization. The critical analysis of research on difficulties continues in the next chapter where it will concern even more abstract concepts in acid-base chemistry.
CHAPTER 8
SYNTHESIS OF STUDENT DIFFICULTIES AND PROPOSITIONAL KNOWLEDGE REGARDING TERMINOLOGY AND SYMBOLISM
IN ACID-BASE CHEMISTRY