Scientific Terminology and Symbols - Essentials of Chemical Education - page 209

Fig. 7.9 Johnstone's triangle for chemical education [ 15 ]

Fig. 7.10 Beaker diagram
for the neutralization of an
acidic solution

the representational level when she writes: “The primary barrier to understanding
chemistry, however, is not the existence of the three levels of representing matter.
It is that chemistry introduction occurs predominately on the most abstract level,
the symbolic level” [ 16 ].
One example for these difficulties is the way the neutralization of acids and bases
is often introduced: the teacher shows that the indicator color changes when adding
drops of sodium hydroxide solution to a sample of hydrochloric acid (macro level)
and writes the equation HCl + NaOH

NaCl + H 2 O (symbolic level) on the
blackboard. Students asked about the particles which are involved in the neutrali-
zation reaction mostly state: “HCl molecules or NaOH molecules” - the direct way
from the phenomena to chemical symbols develops misconceptions. Instead
a “beaker model” (see Fig. 7.10 ) with hydrated ions in both solutions can be
drawn after observing the phenomena. Students will discover that only hydronium
ions react with hydroxide ions to form water molecules (submicro level) and would
develop modern chemistry understanding without misconceptions [ 14 ]. Empirical
research also shows that (aq)-symbols are very useful: students understand that ions
are not attracted to each other and bond to molecules because the hydration shells of
the ions compensate the ionic charges and the hydrated ions move like “billiard
spheres on a table.”

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