Chemistry Reference
In-Depth Information
Table 7.3 Description of chemical processes with everyday, expert and symbol language
Everyday language
Scientific language
Symbol language
OH
Þ
2
g
!
Ca
2
þ
(aq) + 2 OH
(aq)
L
(Ca(OH)
2
)
Lime dissolves in
water until
something lies on
the bottom
undissolved
Saturated solution of Calcium
hydroxide is
at equilibrium with the
excess solute; solubility at
20
C: 0.96 g/L water
Ca
2
þ
ð
f
10
6
(mol
3
/L
3
)
¼
8
c
ð
Ca
þ
Þ
¼
0
:
013mol/L
c
ðO
H
Þ
¼
0
:
026mol/L (Normbed
:Þ
Lime water tastes
soapy
Calcium hydroxide solution
colors universal indicator
paper blue, pH-value is
higher than 7
For 0.005 molar calcium hydroxide
solution is valid:
c
ðO
H
Þ
¼
0.01 mol/L,
pH
¼
12.0
{Ca
2+
CO
3
2
}, CaCO
3
Limestone
Burnt lime
Calcium carbonate
{Ca
2+
O
2
}, CaO
Calcium oxide
Production of slaked
lime
calcium oxide (s) +
water
!
calcium
hydroxide (s); exothermic
CaO + H
2
O
!
Ca(OH)
2
;
DH <
0
O
2
+H
2
O
!
2OH
;
DH <
0
(acid-base reaction)
cognitive structure on the basis of previous experience and existing knowledge.
These educational facts apply especially to the extension of everyday language to
scientific terminology and ultimately to chemical symbols. An example of “lime
reactions” should show related differences (see Table
7.3
).
7.2.1 Connecting Everyday Language and Scientific Terminology
Initially phenomena should be described in everyday language and reaction
symbols should be put into words [see (
7.1
) and (
7.2
)]. Molecular and structural
formulae can follow later (see Table
7.3
). If a reasonable amount of terminology
has been learned successfully, corresponding terms should be used when describing
new phenomena. Existing knowledge can thereby be connected to these new
phenomena and the student's existing cognitive structures can be extended. When
the students are familiar with the terms “acid” and “base,” “acidic” and “alkaline,”
or “hydronium ion and hydroxide ion” from the Arrhenius concept, these terms can
be taken up again for the introduction of the Brønsted concept. The terms will be
connected to the smallest particles that donate or accept protons. When the students
are familiar with the terms “donor” and “acceptor” from acid-base reactions, they
can also use them for redox reactions and connect both types of reactions with
“donor-acceptor reactions.”
Concept maps.
Sumfleth [
6
] described the networking of fundamental terms of
chemistry lessons, built such networks, and analyzed them. Figure
7.3
shows two of
these concept maps for systematizations regarding “acid-base reactions, redox
reactions, and donor-acceptor reactions.” These schemata can only be helpful
when the students realize and understand the different meanings of the words and
the arrows between them. Students can be asked in a quiz to build a concept map.
Students have to organize given terms and put arrows between interrelated terms
