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K. Sheppard 37

has argued that texts and teachers are misleading or inaccurate in their presentation of the
concept of pH in that they fail to describe the approximate nature of the scale by omitting
descriptions of the activity of the hydrogen ion. Introductory chemistry texts tend to concentrate
on the solution of numerical problems rather than on understanding the concept of pH. This,
Hawkes suggests, leads to numerical answers to pH calculations that differ substantially from
experimental reality. The treatment of pH by texts is also unsympathetic to any difficulties that
students might have with the concept. For example, in the teacher’s edition of the Wilbraham et
al. chemistry text (1996), teachers are advised that, “For students who have no concept of
logarithms, explain that pH is found by taking the negative of the power (exponent) of the
hydrogen ion concentration and expressing it as a whole number.” (p. 541) Students, who have
no concept of logarithm, can have no adequate conception of pH at this level. The Wilbraham
text contains the implicit assumption that telling somehow equals knowing or understanding, a
belief that permeates much introductory chemistry.
The findings of the present study confirm this. Though several students defined pH as being
+
“–log [H ]” or were able to determine correctly the relationship between pH values and the
hydrogen ion concentration of a solution, only one student could relate the concept of pH
accurately to an actual solution. That students can perform numerical calculations in chemistry,
without the requisite conceptual understanding has been widely described in the literature (see
for instance, Nurrenbern and Pickering, 1987; Lythcott, 1990; Sawrey, 1990) and this seems to
be the case with pH.
The findings of this study show that students do not generally understand that pH: 1) is a
measure of concentration; 2) is not a measure of ‘strength’ nor of ‘powerfulness’; and 3) is a
logarithmic, not a linear scale. This, of course, has important implications for teachers, textbook
writers and chemistry curriculum developers.

Student ideas about neutralization from tasks 1-3
Students in the study were all familiar with the term ‘neutralization’ and all described it as
some form of interaction between an acid and a base. Two students believed that acids were
inherently more ‘powerful’ than bases and would have a greater influence in the process. Most
students suggested that substances with pH values of 7 were neutral. Six students described the
process of neutralization as the physical mixing of an acid with a base and named no products,
drew no equations, and represented the process diagrammatically with unreacted chemical
species. Ten students labeled neutralization as a chemical reaction, six gave considerable detail,
identifying the reacting species, naming the products as water and salt, and explaining it as a
chemical interaction symbolically in equations. Three students described the formation of new
products by the addition of an acid species to a base species, but did not identify the products,
nor could they represent the process with an equation. Their representations of sub-microscopic
events simply showed base particles attached to acid particles. A summary of the students’ ideas
about neutralization is shown in Table 3.

Chemistry Education Research and Practice, 2006, 7 (1), 32-45

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